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Carburetor

A carburetor (also spelled carburettor or carburetter)  is a device used by a gasoline internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the Venturi tube in the main metering circuit, though various other components are also used to provide extra fuel or air in specific circumstances.

Since the 1990s, carburetors have been largely replaced by fuel injection for cars and trucks, but carburetors are still used by some small engines (e.g. lawnmowers, generators, and concrete mixers) and motorcycles. In addition, they are still widely used on piston engine driven aircraft. Diesel engines have always used fuel injection instead of carburetors, as the compression-based combustion of diesel requires the greater precision and pressure of fuel-injection.

Etymology
The name "carburetor" is derived from the verb carburet, which means "to combine with carbon", or, in particular, "to enrich a gas by combining it with carbon or hydrocarbons". Thus a carburetor mixes intake air with hydrocarbon-based fuel, such as petrol or AutoGas (LPG).

The name is spelled "carburetor" in American English and "carburettor" in British English. Colloquial abbreviations include carb in the UK and North America or Carby in Australia.

Operating principle

Air from the atmosphere enters the carburetor (usually via an air cleaner), has fuel added within the carburetor, passes into the inlet manifold, then through the inlet valve(s), and finally into the combustion chamber. Most engines use a single carburetor shared between all of the cylinders, though some high-performance engines historically had multiple carburetors.

The carburetor works on Bernoulli's principle: the static pressure of the intake air reduces at higher speeds, drawing more fuel into the airstream. In most cases (except for the accelerator pump), the driver pressing the throttle pedal does not directly increase the fuel entering the engine. Instead, the airflow through the carburetor increases, which in turn increases the amount of fuel drawn into the intake mixture.

The main disadvantage of basing a carburetor's operation on Bernoulli's Principle is that being a fluid dynamic device, the pressure reduction in a venturi tends to be proportional to the square of the intake airspeed. The fuel jets are much smaller and fuel flow is limited mainly by the fuel's viscosity so that the fuel flow tends to be proportional to the pressure difference. So jets sized for full power tend to starve the engine at lower speed and part throttle. Most commonly this has been corrected by using multiple jets. In SU and other (e.g. Zenith-Stromberg) variable jet carburetors, it was corrected by varying the jet size.

The orientation of the carburetor is a key design consideration. Older engines used updraft carburetors, where the air enters from below the carburetor and exits through the top. From the late 1930s, downdraft carburetors become more commonly used (especially in the United States), along with side draft carburetors (especially in Europe).

Main metering circuit
The main metering circuit consists of a pipe which reduces to a narrows before widening again, forming a venturi (aka "barrel"). Fuel is introduced into the air stream through small tubes (the main jets) at the narrowest part of the venturi, where the air is at its highest speed.

Downstream of the venturi is a throttle (usually in the form of a butterfly valve) which is used to control the amount of air entering the carburetor. In a car, this throttle is connected to the vehicle's throttle pedal, which varies engine speed.

At lesser throttle openings, the air speed through the venturi is insufficient to maintain the fuel flow, therefore the fuel is instead supplied by the carburetor's idle and off-idle circuits.

At greater throttle openings, the speed of air passing through the venturi increases, which lowers the pressure of the air and draws more fuel into the airstream. At the same time, the reduced manifold vacuum results in less fuel flow through the idle and off-idle circuits.

Choke
During cold weather fuel vaporizes less readily and tends to condense on the walls of the intake manifold, starving the cylinders of fuel and making cold starts difficult. Additional fuel is required (for a given amount of air) to start and run the engine until it warms up, provided by a choke valve.

While the engine is warming up the choke valve is partially closed, restricting the flow of air at the entrance to the carburetor. This increases the vacuum in the main metering circuit, causing more fuel to be supplied to the engine via the main jets. Prior to the late 1950s the choke was manually operated by the driver, often using a lever or knob on the dashboard. Since then, automatic chokes became more commonplace. These either use a bimetallic thermostat to automatically regulate the choke based on the temperature of the engine's coolant liquid, an electrical resistance heater to do so, or air drawn through a tube connected to an engine exhaust source. A choke left closed after the engine has warmed up increases the engine's fuel consumption and exhaust gas emissions, and causes the engine to run rough and lack power due to an over-rich fuel mixture.

However, excessive fuel can flood an engine and prevent it from starting. To remove the excess fuel, many carburetors with automatic chokes allow it to be held open (by manually, depressing the accelerator pedal to the floor and briefly holding it there while cranking the starter) to allow extra air into the engine until the excess fuel is cleared out.

Another method used by carburetors to improve the operation of a cold engine is a fast idle cam, which is connected to the choke and prevents the throttle from closing fully while the choke is in operation. The resulting increase in idle speed provides a more stable idle for a cold engine (by better atomizing the cold fuel) and helps the engine warm up quicker.

Idle circuit
The system within a carburetor that meters fuel when the engine is running at low RPM. The idle circuit is generally activated by vacuum under the throttle plate, which causes a low-pressure area in the idle passage/port thus causing fuel to flow through the idle jet. The idle jet is set at some constant value by the carburetor manufacturer, thus flowing a specified amount of fuel.

Off-idle circuit
Many carburetors use an off-idle circuit, which includes an additional fuel jet which is briefly used as the throttle starts to open. This jet is located in a low-pressure area behind the throttle. The additional fuel it provides is used to compensate for the reduced vacuum that occurs when the throttle is opened, thus smoothing the transition from the idle circuit to the main metering circuit.

Power valve
In a four-stroke engine it is often desirable to provide extra fuel to the engine at high loads (to increase the power output and reduce engine knocking). A 'power valve', which is a spring-loaded valve in the carburetor that is held shut by engine vacuum, is often used to do so. As the airflow through the carburetor increases the reduced manifold vacuum pulls the power valve open, allowing more fuel into the main metering circuit.

In a two-stroke engine, the carburetor power valve operates in the opposite manner: in most circumstances the valve allows extra fuel into the engine, then at a certain engine RPM it closes to reduce the fuel entering the engine. This is done in order to extend the engine's maximum RPM, since many two-stroke engines can temporarily achieve higher RPM with a leaner air-fuel ratio.

This is not to be confused with the unrelated exhaust power valve arrangements used on two-stroke engines.

Metering rod / step-up rod
A metering rod or step-up rod system is sometimes used as an alternative to a power valve in a four-stroke engine in order to supply extra fuel at high loads. One end of the rods is tapered, which sits in the main metering jets and acts as a valve for fuel flow in the jets. At high engine loads, the rods are lifted away from the jets (either mechanically or using manifold vacuum), increasing the volume of fuel can flow through the jet. These systems have been used by the Rochester Quadra jet and in the 1950s Carter carburetors.

Accelerator pump
While the main metering circuit can adequately supply fuel to the engine in steady-state conditions, the inertia of fuel (being higher than that of air) causes a temporary shortfall as the throttle is opened. Therefore, an accelerator pump is often used to briefly provide extra fuel as the throttle is opened. When the driver presses the throttle pedal, a small piston or diaphragm pump injects extra fuel directly into the carburetor throat.

The accelerator pump can also be used to "prime" an engine with extra fuel prior to attempting a cold start.

Float chamber

In order to ensure an adequate supply at all times, carburetors include a reservoir of fuel, called a "float chamber" or "float bowl". Fuel is delivered to the float chamber by a fuel pump. A floating inlet valve regulates the fuel entering the float chamber, assuring a constant level.

Unlike in a fuel injected engine, the fuel system in a carbureted engine is not pressurized. For engines where the intake air travelling through the carburetor is pressurized (such as where the carburetor is downstream of a supercharger) the entire carburetor must be contained in an airtight pressurized box to operate. However, this is not necessary where the carburetor is upstream of the supercharger.

Problems of fuel boiling and vapor lock can occur in carbureted engines, especially in hotter climates. Since the float chamber is located close to the engine, heat from the engine (including for several hours after the engine is shut off) can cause the fuel to heat up to the point of vaporization. This causes air bubbles in the fuel (similar to the air bubbles that necessitate brake bleeding), which prevents the flow of fuel and is known as 'vapor lock'.

To avoid pressurizing the float chamber, vent tubes allow air to enter and exit the float chamber. These tubes usually extend into the carburetor throat, placed to prevent fuel from sloshing out of them into the carburetor.

Diaphragm chamber
If an engine must be operated when the carburetor is not in an upright orientation (for example in a chainsaw or airplane), a float chamber and gravity activated float valve would not be suitable. Instead, a diaphragm chamber is typically used. This consists of a flexible diaphragm on one side of the fuel chamber, connected to a needle valve which regulates the fuel entering the chamber. As the flowrate of the air in the chamber (controlled by the throttling valve/butterfly valve) decreases, the diaphragm moves inward (downward), which closes the needle valve to admit less fuel. As the flowrate of the air in the chamber increases, the diaphragm moves outward (upward) which opens the needle valve to admit more fuel, allowing the engine to generate more power. A balanced state is reached which creates a steady fuel reservoir level, that remains constant in any orientation.

Other components

Other components that have been used on carburetors include:
 * Air bleeds allowing air into various portions of the fuel passages, to enhance fuel delivery and vaporization.
 * Fuel flow restrictors in aircraft engines, to prevent fuel starvation during inverted flight.
 * Heated vaporizers to assist with the atomization of the fuel, particularly for engines using kerosene, tractor vaporizing oil or in petrol-paraffin engines
 * Early fuel evaporators
 * Feedback carburetors, which adjusted the fuel/air mixture in response to signals from an oxygen sensor, in order to allow a catalytic converter to be used
 * Constant vacuum carburetors (also called variable choke carburetors), whereby the throttle cable is connected directly to the throttle cable plate. Pulling the cord caused raw gasoline to enter the carburetor, creating a large emission of hydrocarbons.
 * Constant velocity carburetors use a variable throttle closure in the intake air stream before the accelerator pedal operated the throttle plate. This variable closure is controlled by intake manifold pressure/vacuum. This pressure-controlled throttle provides relatively even intake pressure throughout the engine's speed and load ranges.

Two-barrel and four-barrel designs

The basic design for a carburetor consists of a single venturi (main metering circuit), though designs with two or four venturi (two-barrel and four-barrel carburetors respectively) are also quite commonplace. Typically the barrels consist of "primary" barrel(s) used for lower load situations and secondary barrel(s) activating when required to provide additional air/fuel at higher loads. The primary and secondary venturi are often sized differently and incorporate different features to suit the situations in which they are used.

Many four-barrel carburetors use two primary and two secondary barrels. A four-barrel design of two primary and two secondary barrels was commonly used in V8 engines to conserve fuel at low engine speeds while still affording an adequate supply at high.

The use of multiple carburetors (e.g., a carburetor for each cylinder or pair of cylinders) also results in the intake air being drawn through multiple venturi. Some high-performance engines have used multiple two-barrel or four-barrel carburetors, for example six two-barrel carburetors on Ferrari V12s.

History
In 1826, American engineer Samuel Morey received a patent for a "gas or vapor engine", which ran on turpentine mixed with air. The design did not reach production. In 1875 German engineer Siegfried Marcus produced a car powered by the first petrol engine (which also debuted the first magneto ignition system). Karl Benz introduced his single-cylinder four-stroke powered Benz Patent-Motorwagen in 1885.

All three of these engines used surface carburetors, which operated by moving air across the top of a vessel containing the fuel.

The first float-fed carburetor design, which used an atomizer nozzle, was introduced by German engineers Wilhelm Maybach and Gottlieb Daimler in their 1885 Grandfather Clock engine. The Butler Petrol Cycle car—built in England in 1888—also used a float-fed carburetor.

The first carburetor for a stationary engine was patented in 1893 by Hungarian engineers János Csonka and Donát Bánki.

The first four-barrel carburetors were the Carter Carburetor WCFB and the identical Rochester 4GC, introduced in various General Motors models for 1952. Oldsmobile referred the new carburetor as the "Quadri-Jet" (original spelling) while Buick called it the "Airpower".

In the United States, carburetors were the common method of fuel delivery for most US-made gasoline (petrol) engines until the late 1980s, when fuel injection became the preferred method. One of the last motorsport users of carburetors was NASCAR, which switched to electronic fuel injection after the 2011 Sprint Cup series.

In Europe, carburetors were largely replaced by fuel injection in the late 1980s, although fuel injection had been increasingly used in luxury cars and sports cars since the 1970s. EEC legislation required all vehicles sold and produced in member countries to have a catalytic converter after December 1992. This legislation had been in the pipeline for some time, with many cars becoming available with catalytic converters or fuel injection from around 1990.

Icing in aircraft engine carburetors

A significant concern for aircraft engines is the formation of ice inside the carburetor. The temperature of air within the carburetor can be reduced by up to 40 °C (72 °F), due to a combination of the reduced air pressure in the venturi and the latent heat of the evaporating fuel. The conditions during the descent to landing are particularly conducive to icing, since the engine is run at idle for a prolonged period with the throttle closed. Icing can also occur in cruise conditions at altitude.

A carburetor heat system is often used to prevent icing. This system consists of a secondary air intake which passes around the exhaust, in order to heat the air before it enters the carburetor. Typically, the system is operated by the pilot manually switching the intake air to travel via the heated intake path as required. The carburetor heat system reduces the power output (due to the lower density of heated air) and causes the intake air filter to be bypassed, therefore the system is only used when there is a risk of icing.

If the engine is operating at idle RPM, another method to prevent icing is to periodically open the throttle, which increases the air temperature within the carburetor.

Carburetor icing also occurs on other applications and various methods have been employed to solve this problem. On inline engines the intake and exhaust manifolds are on the same side of the head. Heat from the exhaust is used to warm the intake manifold and in turn the carburetor. On V configurations, exhaust gases were directed from one head through the intake cross over to the other head. One method for regulating the exhaust flow on the cross over for intake warming was a weighted eccentric butterfly valve called a heat riser that remained closed at idle and opened at higher exhaust flow. Some vehicles used a heat stove around the exhaust manifold. It was connected to the air filter intake via tubing and supplied warmed air to the air filter. A vacuum controlled butterfly valve pre heat tube on the intake horn of the air cleaner would open allowing cooler air when engine load increased.

title: Carburetor


text: Talk:Puzzle Bobble

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Talk:Puzzle Bobble


text:
Talk:Processor design

Reference list
How do you edit the reference list so the bullet points and numbers match? The reference list automatically puts a number to the references but what do you do for the articles that are just a bare url with a bullet point?

 * Find the claims for which the "just a bullet point" references are supposed to support (for example, by finding the edit that added the reference), and, for the first such claim for a given reference, putting after the claim. If there's more than one such claim, give the first such claim's reference a name, by doing, and, for all subsequent claims, doing.

 * See, for example, Citing sources and the pages to which it links.

 * To make it more than just a bare URL, use the appropriate citation template. Guy Harris (talk) 08:34, 24 April 2019 (UTC)

Article needs information about phisical design
there is no information about e.x. what metal is it made of? —Preceding unsigned comment added by 178.73.49.6 (talk) 01:20, 6 February 2011 (UTC)

 * Several different metals.

 * But if you're talking about solid state (transistorized) processors, they're mostly made of semiconductors rather than metals. Guy Harris (talk) 08:41, 24 April 2019 (UTC)

Article needs diagrams

 * I think it is essential for this article to display some diagrams that condense and clarify the explanations. I think it's a daunting task to try to understand processor architecture concepts and examples without diagrams. Technical users will have no trouble understanding this immense desolate text, but 'casual' readers and researchers (most people I guess) will likely be disheartened and confused. Can someone with some knowledge in the subject upload/make some simple diagrams? --Cbohorquezm 21:00, 8 May 2006 (UTC)

 * this article could use some pics/diagrams. -- ZeWrestler  Talk 04:38, 3 October 2005 (UTC)

Old discussion
Okay, a pretty big edit. Divided the article into sections. Added a bunch of stuff, cleared up the difference between pipelining and superscalar. I think an improved opening paragraph (betwee "general cpu design" and "1960") would be helpful... might do it later. The stuff at the end (under "additional considerations"), some of it I don't think is appropriate for discussions on CPU design (such as the laser-diode bus replacement...). Also, I don't know much about embedded processor design, so I just left that in its own section at the bottom.

Would it be a good idea to have sample designs under each part? Like "486" as an example of a pipelined processor, "Pentium Pro" as an example scalar processor, and Pentium(II? III? I forget) as an example super-scalar processor?

Also, would it be more appropriate to divide this into multiple articles... like an article on instruction pipelining, and take out most of the discussion on that, and a seperate one for superscalar desgin, and for VLIW, etc. etc. There's already a lot of overlap between this and the CISC and RISC articles.
 * —This unsigned comment is by Mudlock (talk • contribs) 18:02, 15 April 2002.

 * Well, the Pentium Pro's core design was the basis of both the Pentium II and the Pentium III, and they were all not only superscalar but out-of-order superscalar. The original Pentium was superscalar, but not out-of-order. Guy Harris (talk) 08:46, 24 April 2019 (UTC)

What is a "one-off design"? This does not seem to be in English. David 20:21 Nov 13, 2002 (UTC)

If no one replies, I'll delete it. David 22:36 Nov 19, 2002 (UTC)

The topic of this article is CPU design. Several paragraphs at the end of the article are not relevant to CPU design but to Computer Architecture, a different topic. I suggest they be deleted. Namely the paragraphs talking about real-time schedulers, and virtual memory. Aug 17, 2004.

''Deleted ? No, I *moved* them to computer architecture. --DavidCary 22:51, 17 Aug 2004 (UTC)''

 * the article refers to "solid-state RAM"... is there any other (relevent) kind? i guess you can make mechanical logic, and thus, mechanical SRAM, but i don't think thats what the author has in mind.

As a matter of fact- CRTs were used as RAM. Up until that point, acoustic delay lines were used for computer memory. It was awfully slow to wait for the right bits to come around. Core memory was the first solid-state RAM, embraced because it worked so much better than CRT-based RAM.

best-selling CPUs
I removed some text that seemed inaccurate to me. The author had 32-bit ARMs universally replacing 8-bit processors. Engineers use what's cheapest, and 8-bit CPUs and cores are often smaller and cheaper. Embedded defibrillators, one of the lowest-powered devices on the planet (16 nanoamperes draw), generally use a CMOS CISC core of the 68HC11. The last time I checked, the world's best-selling CPU was an 8-bit CISC microcontroller, the Motoroloa 6809. Also, the 6502 is an 8-bit RISC machine, not a CISC. The 6502 even uses combinatorial decoding of instructions, with no microcode. The Acorn RISC Machine (ARM) was designed as a 32-bit 6502.

''I think it's debatable whether the 6502 is RISC or CISC. The 6502 has variable-length instructions (RISC almost all have fixed-length instructions), and a few instructions that do 2 zero-page memory reads and a general memory write (RISC almost all have at most a single memory reference per instruction). --DavidCary 22:51, 17 Aug 2004 (UTC)''

 * It would be really cool to have a historical table of the world's best-selling CPU (and its volume) year-by-year. --DavidCary 22:51, 17 Aug 2004 (UTC)

 * After further thought, I think Talk:List of common microcontrollers is a better place for discussing the variety of best-selling CPUs over the years, and their volume. --DavidCary (talk) 06:14, 28 June 2014 (UTC)

data processing capabilities and bcd
The article says that "the S/360 [had] the first instruction set designed for data processing, rather than mathematical calculation.  I do not believe that this is accurate, given the instruction of the UNIVAC I, the IBM 1401 and others, where mathematical calculations were definitely NOT the only objective.

Additionally, the article states that "the S/360 system was the first computer to make major use of binary coded decimal". Again, to contradict this, the 1401, a predecessor of the S/360 used BCD for its numerical format, as did the IBM 1620.

 * It no longer says either of those, which is appropriate, given that, as you note, both those claims are false. Guy Harris (talk) 08:25, 24 April 2019 (UTC)

No mention of out-of-order execution
This article is missing the major computer architecture topic of the 90's - out-of-order execution. It jumps from superscalar to speculative execution & VLIW (neither technique fully successful in the market) while out-of-order chips are selling in the 100's of millions each year (complete success). It was the complexity of OOO execution which started VLIW to be re-examined by research. Dyl 06:34, Aug 12, 2004 (UTC)

a large bed
The article currently says

 * IBM does have a large bed, VERY large. Of course, on the other hand, IBM may sort of NEED to get all of these customers on-board if they want to stay on top of the CPU development game.

Huh ? What do you mean by "bed" ? --DavidCary 22:51, 17 Aug 2004 (UTC)

Those few paragraphs talking about IBM are: So in my opinion, are not appropriate for this article. Dyl 22:47, Sep 22, 2004 (UTC)
 * not NPOV
 * talk about the economics of processor manufacture, not CPU design directly (or even computer architecture)

 * And that stuff was removed. Guy Harris (talk) 08:47, 24 April 2019 (UTC)

feature proximity
i was going to make a stub for Feature proximity but figured it might be better to just put a sentence about it in an existing article? research.sun.com

thoughts? - Brewthatistrue 23:53, 24 Jun 2005 (UTC)

Sounds blue sky, but that doesn't stop mention in articles. It doesn't belong in the CPU design article, though. Maybe in the Packaging section of Integrated circuit. -R. S. Shaw 02:33, 25 Jun 2005 (UTC)

more futuristic ideas
"Baby Steps to our Future: Future Microprocessors" by Ron Fenley http://www.hal-pc.org/journal/03feb/column/baby/baby.html

split this page?
I'm thinking about splitting this page into multiple articles: The title "design" doesn't match most of the contents, which is computer architecture/microarchitecture. Comments? Dyl 07:27, 1 February 2006 (UTC)
 * 1) History of General Purpose CPUs
 * 2) CPU Design (current sections on actually how to build a CPU)
 * 3) CPU Architectural concepts
 * 4) Embedded CPUs

 * This article could definitely use refocusing. Regarding the mentioned subject areas:
 * History of General Purpose CPUs
 * This is already very well covered by History of computing hardware and Central processing unit, both of which are substantial articles which have reached Featured Article status. The only history this article might need is that of design tecniques, not the CPU products.
 * CPU Design (current sections on actually how to build a CPU)
 * Yes, this should be the content of this article.
 * CPU Architectural concepts
 * These matters should be in a separate article. There already exists an article Computer architecture, which is in great need of additional and better material. Applicable text in this article should be removed and merged into Computer architecture (or conceivably other articles in Category:Computer architecture).  There is also a Microarchitecture article that deals with the physical CPU architecture.
 * Embedded CPUs
 * This likely could go into the design section of Embedded system. There is also Microcontroller.
 * -R. S. Shaw 04:27, 2 February 2006 (UTC)

 * Too small, splitup not justified.  Said: Rursus   ☻   08:19, 9 June 2008 (UTC)

myth of smaller sets of instructions
This article (currently) perpetuates the myth that the "reduced" in RISC means that there are fewer instructions in the instruction set.

I'm pretty sure that the people designing RISC processors didn't really care too much about how many instructions were in the instruction set.

Instead, designers tried to simplify, or "reduce", individual instructions so that individual instructions could be executed very fast. "Fast" in 2 ways:
 * try to get things "done" as quickly as possible after one clock tick -- so that they could reduce the time from one clock tick to the next. Since the clock speed of a CPU is limited by the *slowest* instruction, even if the program currently running on it never uses that instruction, simplifying that one instruction (perhaps by breaking it into 2 or 3 new instructions, expanding the instruction set) allows one to speed up the clock speed, speeding up all the other instructions.
 * try to change the hardware so instructions executed in fewer clock ticks (preferably in a single cycle). Having a fixed limit of "all instructions execute in 1 cycle" also simplifies pipelining and eliminates microcode, indirectly leading to faster clock speed.

Since this seems to be a common myth, should we discuss the myth in the article? (I see it is already discussed in Reduced instruction set computer). --70.189.77.59 13:15, 15 October 2006 (UTC)

High-end processor economics
Under this heading:

4 Markets 4.1 General Purpose Computing 4.1.1 High-end processor economics

I'm not sure if Fujitsu is making it's own high-end processors. If it is a source needs to be added. Thanks. Scifiintel 18:55, 25 February 2007 (UTC)

 * In the article, I just added the external link for it . Dyl 13:19, 26 February 2007 (UTC)

clockless CPUs
The sequential logic article currently links to , a section of this article that apparently no longer exists. To which article has that information moved? Or was it accidentally deleted and needs to be restored? --75.37.227.177 04:53, 26 July 2007 (UTC)

As far as I can tell, that section was accidentally deleted in this summary-less edit: http://en.wikipedia.org/w/index.php?title=CPU_design&diff=prev&oldid=109091120 . So I am restoring that accidental deletion. If it was really *moved* to some other article, not deleted, please tell me to where it moved. --68.0.124.33 (talk) 02:28, 13 February 2008 (UTC)

I see now there are 2 copies of that "clockless CPU" section. One here in "CPU design". The other in History of general purpose CPUs. What should we do about it? --68.0.124.33 (talk) 04:08, 13 February 2008 (UTC)

 * The deletion in Feb '07 was not accidental. You can see that user:Dyl added it to History of general purpose CPUs in this edit the same day the text was deleted from here. (He failed to note this in the latter edit summary, although the former indicates it.) The text needs to be in the right place and deleted from the other(s).  Sequential logic can point whereever it ends up.  I didn't think it fit well in this article, but it doesn't seem to fit all that well in the history article either.  Maybe it belongs in some third article. -R. S. Shaw (talk) 06:43, 13 February 2008 (UTC)

 * Yes I moved that content. This article is a brief introduction to this topic. I didn't see the sense of including a few areas of very esoteric research. These specific areas (optical and clockless) are very far from the mainstream. There are many other areas of research that are more popular - chip-multiprocessing, run-ahead fetching, etc. Dyl (talk) 06:45, 14 February 2008 (UTC)

 * Thank you, Dyl. That makes sense. So I'll re-move that content from this article to History of general purpose CPUs. --68.0.124.33 (talk) 05:46, 22 April 2008 (UTC)

 * Forgive me for moving that "asynchronous CPU" content yet again, to asynchronous circuit. --68.0.124.33 (talk) 01:27, 5 May 2008 (UTC)

needs refs
I found this a very interesting article to read, but it lacks refs. I've placed one fact tag in the economics section, but it really needs more. I'm hesitant to add the refimprove or related tags. Yngvarr 13:54, 31 August 2007 (UTC)

Proposed merger
The merger tag occured without anyone explaining why. Typical! A note and a reason should be put here, when placing a merger tag on the page, uglifying it. I think that a merger is unjustified. It's a common practice to have a short overview section in a main article and a longer detailed article on a more specific topic. I think the state as it is now, is pretty OK. However: the text in Central_processing_unit could, if a mayhap editor get an arbitrary impulse to do so, be shrinked, and text moved to CPU design; or the other way around. It's not necessary to ask, or get a consensus over such a thing. Just do it! (Be bold!) Waiting for consensuses just takes a lot of time, sometimes to no avail. Use consensus as a tool mainly when conflicts arise.  Said: Rursus   ☻   08:30, 9 June 2008 (UTC)

Too shallow on a too abstract level
I would like to have some "child-taleish" description like, the CPU has one or more registers, usually called A, B, C and similar. The CPU works by, one by one in sequence, pick an opcode from a list of opcodes, which is the program. The opcode is "interpreted" in a certain way, so that "F3" represents adding the value in B to A, setting the flags this-or-that if the number overflows, or "E8" "something" represents loading a value from memory at position numbered something.

The tale should go as following: Then maybe a stop (?)
 * 1) CPU has registers/accumulators who are ... ,
 * 2) CPU reads a sequence of opcodes this that ... ,
 * 3) the PC (program counter) is a register that CPU keeps, in order to remember where in program code it picks opcode instructions ...,
 * 4) values can be added to or subtracted from PC, the instructions are called JUMP-this, JREL-that, in short "jumps", when such values are added, the CPU resumes execution at another place in the code,
 * 5) the SP (stack pointer) is another register that CPU uses to save and restore values,
 * 6) ... similar as for jumps but regarding CALLs/RETURNs involving saving position before calling ...

Related topic: Anybody who knows how many general CPU registers (SP, PC, cache and similar uncounted) that this or that CPU family has? It seems to me that the Intel family x86 has EAX, EBX, ECX and EDX summing to four. PowerPC? RSx000 (Nintendo?)? 68x00?  Said: Rursus   ☻   08:47, 9 June 2008 (UTC)

 * I think that x86 has 8 general purpose registers, x64 has 16 and the RISC architectures (Alpha, MIPS, Power, SPARC and HP-PA) has 32 fixed point registers along with 32 floating point registers. Earlier revisions of SPARC and HP-PA may have less though, but I can't remeber how many. Rilak (talk) 08:58, 9 June 2008 (UTC)

 * Very good, thanks! I'll take a look outside WP to find relevant sources. Regarding my own proposal of content: its partially already written (on an abstract level) in Central processing unit, so the proposal can safely be ignored, until it reoccurs on Talk:Central processing unit. Cheers!  Said: Rursus   ☻   10:01, 9 June 2008 (UTC)

 * Rilak and Rursus, a table in the processor register article would be a good place to put your information comparing various processors by number of registers. --68.0.124.33 (talk) 06:54, 6 January 2009 (UTC)

Embedded Design
I've added some clarification to the embedded design section. The most significant change was the statement that embedded devices have a lifetime of several years whilst general-purpose processors "rarely stay in production for more than two years due to the rapid pace of progress". This implied that embedded processors do not have a rapid pace of progress, and this isn't the case. Some embedded processors do remain in use for several years, but this is better explained by the fact that many embedded applications have static requirements, and the cost of replacing the processor in a design is prohibitively high compared to the benefits.

Jacob (talk) 13:49, 22 September 2008 (UTC)

how many people does it take to make a CPU?
I think this article about "CPU design" should answer the question "how many people does it take to design a CPU?". The article says "Assuming that 100 engineers are needed to design a CPU and the project takes 4 years." but gives no references for those numbers.

I posted some information on how many people it actually did take to make a few famous CPUs. To meet Verifiability, I added references to back up the numbers I posted. But I put that information in the wrong section of the article -- oops!

That information was deleted. I succumbed to temptation and reverted that edit, moving those references to a different (still not quite correct!) section of the article. Some, but not all of that information was again deleted.

Am I mistaken in thinking that an article titled "CPU design" should mention how many people it takes to design a CPU? --68.0.124.33 (talk) 04:47, 8 March 2009 (UTC)

 * No, the article should say how many people it takes to design a CPU. I removed some of the information because they did not belong in the sections where they were presented. Ideally, the article should discuss how the resources required for designing CPUs in each market (high-end, embedded, etc.) has evolved. In regards to the unreferenced section about high-end processor economics, I have added an unsourced tag. Rilak (talk) 05:11, 8 March 2009 (UTC)

 * I created the high-end processor economics section. Having worked on multiple CPU development projects over a couple of decades, I know the numbers are accurate. You won't find much published sources as companies consider such costs as proprietary information. Dyl (talk) 06:39, 8 March 2009 (UTC)

 * Yes, I did not expect there to be exact numbers, but are there no discussions about the general cost of CPU development? Rilak (talk) 07:10, 8 March 2009 (UTC)

 * Not that I am aware of. It's not too flattering nor comforting to your customers when the next generation development becomes too expensive to be affordable. Companies like Intel will bring these points up in private when spreading FUD on their competition, but this reality is almost never discussed in public. Dyl (talk) 23:45, 8 March 2009 (UTC)

 * OK. So you rather have the unreferenced tag removed? Rilak (talk) 03:04, 9 March 2009 (UTC)

 * Well, it depends if somebody is willing to do some research. There might be some old EETimes articles which did color commentary within design teams and mentioned the team size in passing. Other than that, I don't know any other references there might be. Dyl (talk) 03:36, 9 March 2009 (UTC)

 * The research sounds rather time-intensive... I think I will pass. If this helps, I do remember an article discussing the closure of an Intel Corp. design centre somewhere in ~2005? If I remember the details right, they were doing a further development of an existing design and had some 800 people, but I don't think they were all engineers. Rilak (talk) 03:54, 9 March 2009 (UTC)

 * Since you haven't come up with any better references, I restored what little WP:SOURCE information I have on "how many people does it take to design a CPU". Hopefully I put it in the right section this time ... --68.0.124.33 (talk) 13:06, 25 March 2009 (UTC)

 * I don't see how that section or manpower statistics in the embedded section is relevant in any way. Those school projects aren't much more than a programming class requirement of writing a simple draw program - what you can achieve in a few hours in a lab, not the hundreds of man-months needed to produce a sellable product. None of these school projects are of the scale of any current-day CPU that you would buy. Dyl (talk) 07:27, 26 March 2009 (UTC)

Unindent

I think it was added to show that a CPU can be designed and implemented with very little resources. Perhaps it should be made more clear that those CPUs are in no way in the same boat as commercial designs. I don't think that having a small section detailing the other end of CPU design can be a bad thing. It would not be a good thing if someone read this article and goes away thinking that CPUs can only be designed by five hundred people over five years, would it? Rilak (talk) 05:27, 27 March 2009 (UTC)

 * I'm more worried that uninformed readers will think any CPU they would currently buy could be designed by two students. Also, for most of these classes, the project is to design just a portion of a CPU, eg. a simple integer ALU. Again, it's like having the Microsoft office or Firefox article saying that computer science students can write a draw program. What's the point? It would be more useful to post the team sizes of embedded CPU teams. Dyl (talk) 07:58, 28 March 2009 (UTC)

 * I see your point. The section has been removed. Rilak (talk) 01:51, 29 March 2009 (UTC)

 * I think this article about "CPU design" should answer the question "how many people does it take to design a CPU?".
 * I agree that there are many classes where students design "just a portion of a CPU".
 * However, there are some classes where students have designed and built various complete, although simple, CPUs -- not merely "design just a portion".
 * You might argue that it is merely my opinion that those student-designed-and-built CPUs are "relevant" to CPU design or "in the same boat as a real CPU". You may be surprised at what our WP:YESPOV policy says about such opinions: The elimination of article content cannot be justified under this policy on the grounds that it is "POV".
 * I agree that it would be useful to post the team sizes of embedded CPU teams. But I already did that.
 * Since Wikipedia is not paper (WP:NOTPAPER), I think there is room in Wikipedia to describe both amazingly complex high-end commercial CPUs, and simple-but-complete low-end CPUs -- just as there is room in the bridge article to mention both amazingly complex and expensive high-end bridges, and simple rope bridges. --68.0.124.33 (talk) 05:15, 4 May 2009 (UTC)

Tags
This article is bad. Its so bad, that it would take me too long, to explain. There is nearly nothing which can be seen as good or sufficient. An expert needs hours; i do not invest them. Tagremover (talk) 16:07, 20 March 2012 (UTC) Structure improved. Tagremover (talk) 16:45, 20 March 2012 (UTC)

Although it is generally unwanted, i propose this article could be improved by a little bit essay-style. Tagremover (talk) 16:13, 20 March 2013 (UTC)

permission to use an instruction set
I see -- in Talk:ARM_Holdings; SAS Institute Inc. v World Programming Ltd; Oracle v. Google; etc. -- that at least some people seem to think that "buying permission to use [an] instruction set" is a normal and common practice.

I was under the impression that no one needs permission to use an instruction set or any other programming language. (Perhaps ARM holdings actually sells detailed test suite torture tests and other validation tools and engineering technical support for their instruction sets, and someone oversimplifies this to "buying an instruction set", which is then misinterpreted as "buying permission to use an instruction set"?). Am I interpreting Oracle v. Google and SAS Institute Inc. v World Programming Ltd incorrectly? (Is an instruction set something that can be copyrighted? patented? mask work protected? trademarked? What parts of a processor design fall into the various intellectual property categories?)

While I am very happy that this article focuses on technical information, I wish someone who understands the business and legal issues -- i.e., someone who is not me -- to say a few words in this article about how one might buy or sell an instruction set -- or whatever it is that Qualcomm bought from ARM Holdings; Microchip Technology bought from MIPS Technologies, etc. --DavidCary (talk) 05:45, 23 July 2014 (UTC)

 * At least some aspects of an instruction set appear to be patentable, as Lexra found to their annoyance. Platform Solutions, Inc. had similar issues courtesy of patent 5,595,709, patent 5,825,679, patent 5,953,520, patent 5,987,495, and patent 6,801,993.  I don't know what patents ARM holds, if any, that one would need to license in order to implement an ARM instruction set architecture, nor what patents Intel has on pre-x86-64 x86 and AMD has on x86-64 that required cross-licensing.  It appears that Intel and HP have patented a number of aspects of the Itanium architecture.

 * And, for what it's worth, both ARM Holdings and its architecture licensees appear to think that buying permission to implement the ARM instruction set themselves isn't a weird and exotic practice. Most ARM licensees license ARM's implementations, so maybe it's not normal or common, but it's certainly not something so exotic as to be dismissed as lunatic. — Preceding unsigned comment added by Guy Harris (talk • contribs) 9:37, 23 July 2014 (UTC)

 * I'm not denying the fact that people who make ARM-compatible chips pay bunch of money to ARM Holdings, and that such payments are a common practice -- even for people who re-implement the ARM instruction set "from scratch" with clean room design.
 * I'm just trying to reconcile that fact with Oracle v. Google and SAS Institute Inc. v World Programming Ltd which seem to say that programming languages as a whole cannot be patented.
 * One way to reconcile these facts is to say that "buying permission to use [an] instruction set" is a simplification, and it would be more accurate for this article to say something like Some features of some instruction sets are patented, and manufacturers are legally required to license (buy permission to use) those patented ideas before selling processors that use those ideas. Often the name of the instruction set is trademarked, and manufacturers license (buy permission to use) that name to use in advertisements for their chip.".
 * Another way to reconcile these facts is to say that Oracle v. Google and SAS Institute Inc. v World Programming Ltd don't apply to instruction sets hard-wired into physical CPU chips, and "people are legally required to buy permission to use an instruction set before fabricating and selling chips that use that instruction set".
 * I honestly don't know. I wish this article said something one way or the other.
 * Either way, my understanding is that manufacturers, in addition to "buying permission", also buy test suites and other things, not because they are legally required to, but because it's cheaper than developing their own independent test suites and other things.
 * I wish this article listed all of the things manufacturers typically buy from ARM Holdings and other groups of people that design processors. --DavidCary (talk) 14:23, 30 August 2014 (UTC)

 * If wishes were horses, beggars would ride. Expressing a wish for something gets you nothing unless somebody has the resources to fulfill the wish.

 * One version of the ARM architecture manual says:

 * The product described in this document is subject to continuous developments and improvements. All particulars of the product and its use contained in this document are given by ARM in good faith.

 * 1. Subject to the provisions set out below, ARM hereby grants to you a perpetual, non-exclusive, nontransferable, royalty free, worldwide licence to use this ARM Architecture Reference Manual for the purposes of developing; (i) software applications or operating systems which are targeted to run on microprocessor cores distributed under licence from ARM; (ii) tools which are designed to develop software programs which are targeted to run on microprocessor cores distributed under licence from ARM; (iii) or having developed integrated circuits which incorporate a microprocessor core manufactured under licence from ARM.

 * 2. Except as expressly licensed in Clause 1 you acquire no right, title or interest in the ARM Architecture Reference Manual, or any Intellectual Property therein. In no event shall the licences granted in Clause 1, be construed as granting you expressly or by implication, estoppel or otherwise, licences to any ARM technology other than the ARM Architecture Reference Manual. The licence grant in Clause 1 expressly excludes any rights for you to use or take into use any ARM patents. No right is granted to you under the provisions of Clause 1 to; (i) use the ARM Architecture Reference Manual for the purposes of developing or having developed microprocessor cores or models thereof which are compatible in whole or part with either or both the instructions or programmer's models described in this ARM Architecture Reference Manual; or (ii) develop or have developed models of any microprocessor cores designed by or for ARM; or (iii) distribute in whole or in part this ARM Architecture Reference Manual to third parties, other than to your subcontractors for the purposes of having developed products in accordance with the licence grant in Clause 1 without the express written permission of ARM; or (iv) translate or have translated this ARM Architecture Reference Manual into any other languages.

 * 3.THE ARM ARCHITECTURE REFERENCE MANUAL IS PROVIDED "AS IS" WITH NO WARRANTIES EXPRESS, IMPLIED OR STATUTORY, INCLUDING BUT NOT LIMITED TO ANY WARRANTY OF SATISFACTORY QUALITY, NONINFRINGEMENT OR FITNESS FOR A PARTICULAR PURPOSE.

 * 4. No licence, express, implied or otherwise, is granted to LICENSEE, under the provisions of Clause 1, to use the ARM tradename, in connection with the use of the ARM Architecture Reference Manual or any products based thereon. Nothing in Clause 1 shall be construed as authority for you to make any representations on behalf of ARM in respect of the ARM Architecture Reference Manual or any products based thereon.

 * but they don't indicate what "rights" to "[develop] or [have developed]] microprocessor cores or models thereof which are compatible in whole or part with either or both the instructions or programmer's models described in this ARM Architecture Reference" are involved, what laws require those rights to be explicitly granted by ARM, or who will enforce those rights. Perhaps their only claim that you need them to grant you such a "right" comes from patents they have on features of the ARM architecture, just as, for example. MIPS has patents such as  on features of their architecture, or that they have a trademark on "ARM" and that you can't describe your processor as implementing the "ARM architecture" unless ARM grants you a trademark license to do so. Guy Harris (talk) 04:25, 31 August 2014 (UTC)

Integrated circuit design
I propose to state explicitly that PD is a subfield of Integrated circuit design. Any objections? AXO NOV (talk) ⚑ 09:48, 29 November 2021 (UTC)

 * I think we could qualify it a little, perhaps "microprocessor design is a subfield of integrated circuit design" or "modern commercial processor design is a subfield of integrated circuit design" or "a microprocessor is a kind of integrated circuit".
 * The vast majority of processors are part of a single integrated circuit, so it would seem that processor design is part of integrated circuit design. However, some historically important and influential processors were designed and built without any integrated circuits, such as the IBM Stretch, the Gemini Guidance Computer, PDP-10, etc. Even today, most people designing a new custom processor don't actually design any new integrated circuits (see Microprocessor Design/Wire Wrap for a partial list of both hobbyist and commercial CPUs manufactured without a new IC).
 * So while they almost completely overlap, there is still a little sliver of processor design that seems to be outside of integrated circuit design. (And of course, there is a large amount of integrated circuit design that is completely outside of processor design, such as analog ICs and mixed-signal ICs). --DavidCary (talk) 02:35, 1 December 2021 (UTC)
 * Yes. Most processor design is currently integrated circuit design, but that hasn't been true forever. Guy Harris (talk) 02:43, 1 December 2021 (UTC)
 * That's fair point. I fully support narrowing to . Let me propose then to state that it's a subfield of ICD only if the processor is intended to be built (manufactured) in the silicon. Otherwise it's a subject to circuit design and logic synthesis — generally. It should exclude others ways of logic implementations (e.g. relays, vacuum tubes, etc.) and confusion about it.  AXO NOV  (talk) ⚑ 10:35, 11 December 2021 (UTC)

title: Talk:Processor design


text:
Clef

A clef (from French: clef 'key') is a musical symbol used to indicate which notes are represented by the lines and spaces on a musical staff. Placing a clef on a staff assigns a particular pitch to one of the five lines or four spaces, which defines the pitches on the remaining lines and spaces.

The three clef symbols used in modern music notation are the G-clef, F-clef, and C-clef. Placing these clefs on a line fixes a reference note to that line—an F-clef fixes the F below middle C, a C-clef fixes middle C, and a G-clef fixes the G above middle C. In modern music notation, the G-clef is most frequently seen as treble clef (placing G4 on the second line of the staff), and the F-clef as bass clef (placing F3 on the fourth line). The C-clef is mostly encountered as alto clef (placing middle C on the third line) or tenor clef (middle C on the fourth line). A clef may be placed on a space instead of a line, but this is rare.

The use of different clefs makes it possible to write music for all instruments and voices, regardless of differences in range. Using different clefs for different instruments and voices allows each part to be written comfortably on a staff with a minimum of ledger lines. To this end, the G-clef is used for high parts, the C-clef for middle parts, and the F-clef for low parts. Transposing instruments can be an exception to this—the same clef is generally used for all instruments in a family, regardless of their sounding pitch. For example, even the low saxophones read in treble clef.

A symmetry exists surrounding middle C regarding the F-, C- and G-clefs. C-clef defines middle C whereas G-clef and F-clef define the note at the interval of a fifth above middle C and below middle C, respectively.

Two common mnemonics for learning the clef lines are:
 *  Good Boys Do Fine Always  (bass clef)
 *  Every Good Boy Does Fine (treble clef)

Placement on the staff
Theoretically, any clef may be placed on any line. With five lines on the staff and three clefs, there are fifteen possibilities for clef placement. Six of these are redundant because they result in an identical assignment of the notes—for example, a G-clef on the third line yields the same note placement as a C-clef on the bottom line. Thus there are nine possible distinct clefs when limiting their placement to the lines. All have been used historically: the G-clef on the two bottom lines, the F-clef on the three top lines, and the C-clef on the four bottom lines. The C-clef on the topmost line has also been used, but is equivalent to the F-clef on the third line, giving a total of ten historically attested clefs placed on the lines. In addition, the C-clef has been used on the third space, i.e. not on a line at all.

The ten clefs placed on lines (two are equivalent) have different names based on the tessitura for which they are best suited.

In modern music, only four clefs are used regularly: treble clef, bass clef, alto clef, and tenor clef. Of these, the treble and bass clefs are by far the most common. The tenor clef is used for the upper register of several instruments that usually use bass clef (including cello, bassoon, and trombone), while the alto is most prominently used by the viola. Music for instruments and voices that transpose at the octave is generally written at the transposed pitch, but is sometimes seen written at concert pitch using an octave clef.

Individual clefs
This section shows a complete list of the clefs, along with a list of instruments and voice parts notated with them. A dagger (†) after the name of a clef indicates that the clef is no longer in common use.

Treble clef
The only G-clef still in use is the treble clef, with the G-clef placed on the second line. This is the most common clef in use and is generally the first clef learned by music students. For this reason, the terms "G-clef" and "treble clef" are often seen as synonymous. The treble clef was historically used to mark a treble, or pre-pubescent, voice part.

Instruments that use the treble clef include violin, flute, oboe, cor anglais, all clarinets, all saxophones, horn, trumpet, cornet, vibraphone, xylophone, mandolin, recorder, bagpipe and guitar. Euphonium and baritone horn are sometimes treated as transposing instruments, using the treble clef and sounding a major ninth lower, and are sometimes treated as concert-pitch instruments, using bass clef. The treble clef is also the upper staff of the grand staff used for harp and keyboard instruments. Most high parts for bass-clef instruments (e.g. cello, double bass, bassoon, and trombone) are written in the tenor clef, but very high pitches may be notated in the treble clef. The viola also may use the treble clef for very high notes. The treble clef is used for the soprano, mezzo-soprano, alto, contralto and tenor voices. Tenor voice parts sound an octave lower and are often written using an octave clef (see below) or a double-treble clef.

French violin clef†

A G-clef placed on the first line is called the French clef, or French violin clef. It was used in France in the seventeenth and eighteenth centuries for violin music and flute music. It places the notes in the same staff positions as the bass clef, but two octaves higher.

Baritone clef†

When the F-clef is placed on the third line, it is called the baritone clef. Baritone clef was used for the left hand of keyboard music (particularly in France; see Bauyn manuscript) and for baritone parts in vocal music. A C-clef on the fifth line creates a staff with identical notes to the baritone clef, but this variant is rare.

Bass clef

The only F-clef still in use is the bass clef, with the clef placed on the fourth line. Since it is the only F-clef commonly encountered, the terms "F-clef" and "bass clef" are often regarded as synonymous.

Bass clef is used for the cello, double bass and bass guitar, bassoon and contrabassoon, bass recorder, trombone, tuba, and timpani. It is used for baritone horn or euphonium when their parts are written at concert pitch, and sometimes for the lowest notes of the horn. Baritone and bass voices also use bass clef, and the tenor voice is notated in bass clef if the tenor and bass are written on the same staff. Bass clef is the bottom clef in the grand staff for harp and keyboard instruments. Double bass, bass guitar, and contrabassoon sound an octave lower than the written pitch; some scores show an "8" beneath the clef for these instruments to differentiate from instruments that sound at the actual written pitch. (see "Octave clefs" below).

Sub-bass clef†
When the F-clef is placed on the fifth line, it is called the sub-bass clef. It was used by Johannes Ockeghem and Heinrich Schütz to write low bass parts, by Monsieur de Sainte-Colombe for low notes on the bass viol, and by J. S. Bach in his Musical Offering.

It is the same as the treble clef, but two octaves lower.

Alto clef

A C-clef on the third line of the staff is called the alto or viola clef. It is currently used for viola, viola d'amore, alto trombone, viola da gamba, and mandola. It is also associated with the countertenor voice and sometimes called the countertenor clef. A vestige of this survives in Sergei Prokofiev's use of the clef for the cor anglais in his symphonies. It occasionally appears in keyboard music (for example, in Brahms's Organ Chorales and John Cage's Dream for piano). It was originally used for alto parts in choral music to reduce the number of ledger lines needed, since much of the alto range is between treble and bass clef. Alto parts are now commonly written in treble clef instead.

Tenor clef

A C-clef on the fourth line of the staff is called tenor clef. It is used for the viola da gamba (rarely, and mostly in German scores; otherwise the alto clef is used) and for upper ranges of bass-clef instruments such as the bassoon, cello, euphonium, double bass, and tenor trombone. Treble clef may also be used for the upper extremes of these bass-clef instruments. Tenor violin parts were also written in this clef (see e.g. Giovanni Battista Vitali's Op. 11). It was used by the tenor part in vocal music but its use has been largely supplanted either with an octave version of the treble clef or with bass clef when tenor and bass parts are written on a single staff.

Another tenor clef variant, formerly used in music for male chorus, has a ladder-like shape. This C-clef places the C on the third space of the staff, and is equivalent to the sub-octave treble clef. See also History.

Mezzo-soprano clef†

A C-clef on the second line of the staff is called the mezzo-soprano clef, rarely used in modern Western classical music. It was used in 17th century French orchestral music for the second viola or first tenor part ('taille') by such composers as Lully, and for mezzo-soprano voices in operatic roles, notably by Claudio Monteverdi. Mezzo-soprano clef was also used for certain flute parts during renaissance, especially when doubling vocal lines. In Azerbaijani music, the tar uses this clef.

Soprano clef†

A C-clef on the first line of the staff is called the soprano clef. It was used for the right hand of keyboard music (particularly in France – see Bauyn manuscript), in vocal music for sopranos, and sometimes for high viola da gamba parts along with the alto clef. It was used for the second violin part ('haute-contre') in 17th century French music.

Octave clefs

Starting in the 18th century, music for some instruments (such as guitar) and for the tenor voice have used treble clef, although they sound an octave lower. To avoid ambiguity, modified clefs are sometimes used, especially in choral writing. Using a C-clef on the third space places the notes identically, but this notation is much less common as it is easily confused with the alto and tenor clefs.

Such a modified treble clef is most often found in tenor parts in SATB settings, using a treble clef with the numeral 8 below it. This indicates that the pitches sound an octave lower. As the true tenor clef has fallen into disuse in vocal writings, this "octave-dropped" treble clef is often called the tenor clef. The same clef is sometimes used for the octave mandolin. This can also be indicated with two overlapping G-clefs.

Tenor banjo is commonly notated in treble clef. However, notation varies between the written pitch sounding an octave lower (as in guitar music and called octave pitch in most tenor banjo methods) and music sounding at the written pitch (called actual pitch). An attempt has been made to use a treble clef with a diagonal line through the upper half of the clef to indicate octave pitch, but this is not always used.

To indicate that notes sound an octave higher than written, a treble clef with an 8 positioned above the clef may be used for penny whistle, soprano and sopranino recorder, and other high woodwind parts. A treble clef with a 15 above (sounding two octaves above the standard treble clef) is used for the garklein (sopranissimo) recorder.

An F-clef can also be notated with an octave marker. While the F-clef notated to sound an octave lower can be used for contrabass instruments such as the double bass and contrabassoon, and the F-clef notated to sound an octave higher can be used for the bass recorder, these uses are extremely rare. In Italian scores up to Gioachino Rossini's Overture to William Tell, the cor anglais was written in bass clef an octave lower than sounding. The unmodified bass clef is so common that performers of instruments whose ranges lie below the staff simply learn to read ledger lines.

Neutral clef

The neutral or percussion clef is not a true clef like the F, C, and G clefs. Rather, it assigns different unpitched percussion instruments to the lines and spaces of the staff. With the exception of some common drum-kit and marching percussion layouts, the assignment of lines and spaces to instruments is not standardised, so a legend is required to show which instrument each line or space represents. Pitched percussion instruments do not use this clef — timpani are notated in bass clef and mallet percussion instruments are noted in treble clef or on a grand staff.

If the neutral clef is used for a single percussion instrument the staff may only have one line, although other configurations are used.

The neutral clef is sometimes used where non-percussion instruments play non-pitched extended techniques, such as hitting the body of a string instrument, or having a vocal choir clap, stamp, or snap. However, it is more common to write the rhythms using × noteheads on the instrument's normal staff, with a comment to indicate the appropriate rhythmic action.

Tablature
For guitars and other fretted instruments, it is possible to notate tablature in place of ordinary notes. This TAB sign is not a clef — it does not indicate the placement of notes on a staff. The lines shown are not a music staff but rather represent the strings of the instrument (six lines would be used for guitar, four lines for the bass guitar, etc.), with numbers on the lines showing which fret should be used.

History
Before the advent of clefs, the reference line of a staff was simply labeled with the name of the note it was intended to bear: F, C, or sometimes G. These were the most common 'clefs', or litterae clavis (key-letters), in Gregorian chant notation. Over time the shapes of these letters became stylised, leading to their current versions.

Many other clefs were used, particularly in the early period of chant notation, keyed to many different notes, from the low Γ (gamma, the G on the bottom line of the bass clef) to the G above middle C (written with a small letter g). These included two different lowercase b symbols for the note just below middle C: round for B♭, and square for B♮. In order of frequency of use, these clefs were: F, c, f, C, D, a, g, e, Γ, B, and the round and square b. In later medieval music, the round b was often written in addition to another clef letter to indicate that B♭ rather than B♮ was to be used throughout a piece; this is the origin of the key signature.

In the polyphonic period up to 1600, unusual clefs were occasionally used for parts with extremely high or low tessituras. For very low bass parts, the Γ clef is found on the middle, fourth, or fifth lines of the staff (e.g., in Pierre de La Rue’s Requiem and in a mid-16th-century dance book published by the Hessen brothers); for very high parts, the high-D clef (d), and the even higher ff clef (e.g., in the Mulliner Book) were used to represent the notes written on the fourth and top lines of the treble clef, respectively.

The practice of using different shapes for the same clef persisted until very recent times. The F-clef was, until as late as the 1980s in some cases (such as hymnals), or in British and French publications, written like this:

In printed music from the 16th and 17th centuries, the C clef often assumed a ladder-like form, in which the two horizontal rungs surround the staff line indicated as C: ; this form survived in some printed editions (see this example, written in four-part men's harmony and positioned to make it equivalent to an octave G clef) into the 20th century.

The C-clef was formerly written in a more angular way, sometimes still used, or, more often, as a simplified K-shape when writing the clef by hand:

In modern Gregorian chant notation the C clef is written (on a four-line staff) in the form and the F clef as

The flourish at the top of the G-clef probably derives from a cursive S for "sol", the name for "G" in solfege.

C clefs (along with G, F, Γ, D, and A clefs) were formerly used to notate vocal music. Nominally, the soprano voice parts were written in first- or second-line C clef (soprano clef or mezzo-soprano clef) or second-line G clef (treble clef), the alto or tenor voices in third-line C clef (alto clef), the tenor voice in fourth-line C clef (tenor clef) and the bass voice in third-, fourth- or fifth-line F clef (baritone, bass, or sub-bass clef).

Until the 19th century, the most common arrangement for vocal music used the following clefs:

 * Soprano = soprano clef (first-line C clef)
 * Alto = alto clef (third-line C clef)
 * Tenor = tenor clef (fourth-line C clef)
 * Bass = bass clef (fourth-line F clef)

In more modern publications, four-part music on parallel staffs is usually written more simply as: This may be reduced to two staffs, the soprano and alto sharing a staff with a treble clef, and the tenor and bass sharing a staff marked with the bass clef.
 * Soprano = treble clef (second-line G clef)
 * Alto = treble clef
 * Tenor = treble clef with an 8 below or a double treble clef. Many pieces, particularly those from before the 21st century, use an unaltered treble clef, with the expectation the tenors will still sing an octave lower than notated.
 * Bass = bass clef (fourth-line F clef)

Further uses
Clef combinations played a role in the modal system toward the end of the 16th century, and it has been suggested certain clef combinations in the polyphonic music of 16th-century vocal polyphony are reserved for authentic (odd-numbered) modes, and others for plagal (even-numbered) modes, but the precise implications have been the subject of much scholarly debate.

Reading music as if it were in a different clef from the one indicated can be an aid in transposing music at sight since it will move the pitches roughly in parallel to the written part. Key signatures and accidentals need to be accounted for when this is done.

In Unicode
For use with computer systems, the Unicode Consortium has created code points for twelve different clef symbols as part of a repertoire called the "Musical Symbols" block. Although much of the list was established by 1999, general provision of these symbols in common computer fonts remains rather limited. The clef symbols provided are these:

title: Clef


text:
Talk:Smart growth

Edits 3/27/2008
Removed the following section of article:

"===Economic===

Big-city mayors, downtown business groups, and individual investors interested in gentrification see smart growth or regeneration as a useful tool to revitalize town centers or neglected urban neighborhoods. Rural politicians support it to deter in-migration and change to rural open spaces, although their constituents may work in towns and cities.

Locating people near each other, near jobs, and near shopping, reduces travel time and transportation infrastructure costs. Policy-makers sometimes try to provide financial incentives to developers to encourage different land use choices, often in combination with changing legal requirements.

Smart growth considers the total long-term economic costs of development decisions, rather than merely the short term profits. Engineers often use life cycle cost analysis to evaluate trade-offs, while investors and proprietors may be more interested in the "bottom line" of profitability."

Section was judged to be subjective and logically inconsistent.

Paragraph 1: There is no evidence that 'big-city mayors', 'downtown business groups', 'individual investors', or 'rural politicians' in general support smart growth. This statement can even be construed as counter intuitive, as, for example, rural politicians would discourage smart growth in order to bring economic development to their areas.

Paragraph 2: There is no evidence that smart growth reduces travel time nor infrastructure costs. Smart growth may have the opposite affects: smart growth increases the mode share of transit, walking, and bicycling, all of which in general have longer travel times over similar distances when compared to automobile travel. In addition, not all infrastructure costs can be said to be affected positively by smart growth; there are many studies that suggest fixed transit services (such as those encouraged by smart growth) are more expensive than highway infrastructure both to construct and maintain. The second sentence in this paragraph is irrelevant to both the premise of the first sentence and the section of the article.

Paragraph 3: This paragraph is contradictory. Engineers design the majority of infrastucture, however, the majority of infrastructure is not designed within smart growth parameters. Therefore, if engineers, as the paragraph claims, typically use life cycle cost analysis to arrive at the most efficient design, this suggests that smart growth is inefficient from a life cycle cost analysis perspective.

Undated Edits
Removed part of the article:
 * Supportive of Agenda 21 agreements and the ecology movement's efforts to control sprawl, protect biodiversity and conserve natural habitats, the Smart Growth concept is perceived as a more media-friendly term than notions of sustainability which have perhaps a greater intellectual appeal. It cleverly appears to distance itself from mid 20th century notions of population control or "going back to nature" (which have anti-democratic and anti-capitalist connotations) and accepts that some "growth" is inevitable. It may thus expand its sphere of influence, even though some supporters presumably would prefer "no growth" or the emphatic reversal of many, largely acquisitive, trends perceived as detrimental to social and/or environmental conditions in industrialised democratic societies. It rather allows different supporters to choose what things grow in their personal visions of a better world. As an indication of societal hesitancy, many politicians and academics seem more prepared to argue for a reduced use of private cars than for reduced car (US: automobile) ownership or production. It is clearly less disruptive of the status quo in any society to argue for the cessation of a particular growth trend than to argue for its reversal, even over a long period.

 * One disadvantage of using the term "sustainable" to describe modes of behaviour or commerce that respect ecological understanding and environmental goals is that the same word is often used (especially by politicians and entrepreneurs) to mean sustainable in its traditional sense (i.e. capable of future continuity), or as a synonym for "economically viable". Thus a taxation initiative might be described as "sustainable" because the principle enjoys cross-party agreement or because it appears easy to administer, even though the new tax has no Green benefits and would not deter environmental damage or reduce the depletion of natural resources.

Recent additions need to be qualified and NPOVed. --maveric149

 * Perhaps we have been pounding on 24 a bit too much about NPOV. This EPA writeup seems to use "sustainable" with no sop to business or industry.  Perhaps they abandoned the word because there really is a militant green faction somewhere making some inroads?  Complex issues that is for sure:  *http://216.239.35.100/search?q=cache:lkJBLf_66aEC:www.epa.gov/swerrims/RCRA-ch4.pdf+engineering+economics+discounting+tradeoff&hl=en&lr=lang_en

Well, back to engineering life cycle tradeoffs analysis where I was being confused when I found this, chow maveric,24.

How is this not NPOV? Qualifed how? New draft material below: Apparently useful links from google: http://www.un.org/esa/sustdev/agenda21.htm http://www.un.org/esa/sustdev/agenda21text.htm

Good grief! 2.3X10E6 more links .... this may take some serious research!

Perhaps we should rely on 24s first cut at NPOV and then tweakify it vs. attempting to write from scratch ourselves?

 * The Smart Growth campaign and concept grew out of Agenda 21 agreements and the ecology movement's efforts to control sprawl, protect biodiversity and conserve natural habitats. The Smart Growth concept was designed to be a more media-friendly term influential with viewers than notions of sustainability which have perhaps a greater intellectual appeal, at least among self appointed intellectuals with limited education or exposure to practical disciplines such as applied science, industry or engineering arts in construction and transporation sectors of macroeconomies.  It cleverly attempts to distance itself from mid 20th century notions of population control or "going back to nature" (which have anti-democratic and anti-capitalist connotations) and acknowledges or accepts that some "growth" is inevitable.

 * It is hoped by its originators that this is an improved public relations concept that may assist in expanding its sphere of influence.  Some supporters presumably would still prefer "no growth" or the emphatic reversal of many, largely acquisitive, trends perceived as detrimental to social and/or environmental conditions in industrialised democratic societies.  However, this compromise vision allows practical implementation of current political agendas that may incrementally advance all supporters goals, even though the goals vary in degree and destination. user:mirwin

Moving on to green architecture in the news ... assuming we can find a link from "Smarth Growth" and Agenda 21 (Ok, I admit that I had never heard of it but apparently UN and 178 countries have.) to these success stories:
 * http://www.metropolismag.com/html/content_0801/mcd/index_b.html
 * http://www2.cddc.vt.edu/digitalfordism/11cleanpl.html
 * http://www.delta-institute.org/pollprev/ford.php
 * http://www.greenroofs.com/current_projects.htm

This seems a bit silly. Now I need to go research/find/write about sod busters, sod houses and prairie schooners. The sod roof is back in style because it is potentially cheaper than oil/natural gas heating at current BTU rates. Will wonders never cease? mirwin

How about this:

 * The concept of smart growth grew out of ecology movement's efforts to control sprawl, protect biodiversity and conserve natural habitats. Some view the concept of smart growth as being a more media-friendly term that calls upon notions of sustainability which perhaps have a greater intellectual appeal than some of the more emotional notions that underlie the ecology movement.  Several radio show personalities consider the smart growth movement to be a clever attempt by environmentalists to distance itself from notions like population control and advocacy of communes. In fact, some supporters of the concept of smart growth do prefer "no growth" but maintain that "some growth" is inevitable and should therefore be planned in a way to minimize environmental harm.

 * Looks pretty good to me except I do not like referencing radio show hosts .... to me most seem like ignorant boobs willing to say what it takes to make the big bucks and syndication. How about "Several radio show personalities ...." changing to "Adamant pro grow factions consider the smart growth movement to be merely propaganda and public image management attempting to distance themselves from early radical concepts such as population control and advocacy of alternate lifestyles such as communes.

Also, I wonder if we should have a section that attempts to track the differences in view of urban vs. rural populations. Various methods or ways to proceed have very different impacts on urban and rural voters and it is my perception that this greatly complicates the public debate in the U.S.  What does it do in other industrialized nations in Europe and for that matter in emerging economies elsewhere? Anyone! We need some input here .... [[user:mirwin]

I have attempted to make the language more accessible with descriptions, links and examples. Also have modified for NPOV. I didn't have the patience to address the timeline. I also moved the technical flag to the "talk" section for two reasons -- 1) it said it was misplaced, and 2) I hope I addressed some of the problem. This article continues to need a lot of work. Footnotes would probably be helpful -- I would imagine that the Congress of New Urbanism would be a good source to use in describing what smart growth is, according to its proponents. Because the term "smart growth" was clearly designed as a phrase of advocacy, it is especially important to maintain NPOV in this article. Some discussion of the development of the phrase and its use in advocacy should probably also be addressed more promienently. Thesmothete 23:32, 9 January 2006 (UTC)

Change category name from New Urbanism to...
I have proposed changing the name of Category:New Urbanism. My best alternative is Sustainable urban planning or Sustainable urban design, which would then be broad enough to cover articles such as this one. But perhaps there is something more suitable.

See discussion at Category talk:New Urbanism. (Don't respond here) --Singkong2005 13:57, 30 March 2006 (UTC)

Examples of Communities Implementing Smart Growth Principles
It's not clear to me how helpful this section is becoming, if we have simply an uncited list of cities asserted to be examples of Smart Growth. I would suggest that each listed city should have a cite and/or short explaination as to why it is included in order to stay. Thesmothete 14:43, 19 June 2006 (UTC)

 * It's clear to me that the section, as it stands, is close to useless. Either it needs to be expanded to supply context or the entire list should be removed. The inclusion of Columbus (which finished dead last in a recent should be enough to demonstrate that the current list is not working as intended.  - EurekaLott 05:36, 20 June 2006 (UTC)

 * I've added a list of communities considered to have one or more smart growth principals applied enough to be fouced on by smartgrowth.org. I agree that the cities/communities could afford short explanations as what has been applied and elaborated, rather than just a list, but I disagree that the section is useless, if nothing more than just a starting reference. Shaunjason 16:39, 3 October 2006 (UTC)

 * I have removed the unsourced communities in the list. For a few of those referenced in the Smart Growth Network piece, I have listed their particular noteworthiness, but, frankly, most of them get a passing mention in a document that provides little context for understanding what these communities actually have done.  There are clearly dozens, if not hundreds of communities that could list some claim to having done something related to smart growth, so let's limit this list to those for which we can document either major recognition of overall success or list the particular area of success along with a specific citation. Thesmothete 15:54, 16 October 2006 (UTC)

"Smart Growth" not architecture, this page not technical
I don't see what "Smart Growth" has to do with architecture. It's a planning theory that has little to do with building design.

Likewise, I don't think this page is "too technical". It just lacks substance, and could readily be edited down to a stub or start at best. "Smart Growth" is little more than a slogan for the New Urbanism, and I recommend merging it into that article.

IMHO, "Smart Growth" is primarily an excuse for continuous, excessive, and often unmitigated urban growth, or "vertical sprawl". Most of the arguments for it I've seen are little more than developer propaganda and PR.

I just edited the introduction to one section down to all that it needed to say. I'll try to cut through some more of the BS here as time allows. Mukrkrgsj 03:57, 4 March 2007 (UTC)

 * While I'm no fan of "Smart Growth," tending to agree there's too much emphasis on the second term, it is architecutre related. It's certainly a planning issue, but effective mixed use requires careful design. --Belg4mit 22:24, 19 April 2007 (UTC)

Consistency
"Smart Growth" or smart growth? Both are used in the article. --Belg4mit 22:24, 19 April 2007 (UTC)
 * I recommend "Smart Growth"--it's fundamentally a slogan. -- Mukrkrgsj 01:36, 20 April 2007 (UTC)

Citation needed: Compact neighborhoods
"Compact, livable urban neighborhoods attract more people and business.": this sentence needs a citation. This is a broad contention that needs a reference to support it.

There is considerable literature proving the opposite, especially that people are not generally attracted to compact neighborhoods. While it is accepted that certain micro-demographic nodes (see studies on "cluster demographics") do indeed prefer compact neighborhoods, recent studies employing focus groups indicate that a very large proportion of the American public do prefer lower density neighborhoods, and single-family detached housing in particular.

As well, the term 'liveable' is widely open to interpretation. As the old saying goes "one man's rose is another man's onion". The opening sentence implies that 'compact' and 'liveable' are synonymous with one another. If so, documentation is needed to show the research that proves that the general public sees a 'compact' neighborhood de facto as a 'liveable' one.

It may well be (and again proof is needed; this is just my opinion) that the average American who drives through quaint 'compact' neighborhoods in inner-city Philadelphia or Seattle finds them delightful and fancies that they could live there; that, in other words, they are 'liveable'.

It is quite another thing, however, for that same person to plunk down hundreds of thousands of dollars to purchase a home there and truly find out whether they are 'liveable'. --Atikokan (talk) 06:49, 25 January 2009 (UTC)

Criticism Section Needs Work
I think the Criticism section needs to be reworked to actually present a NPOV abstract of the criticisms. If there are indeed refutations of these criticisms, fine, let's put them in a "Responses to Criticisms" section or similar. Right now, the section pretty much just mentions that criticisms exist without giving a summary of the substance of their argument. Neltana (talk) 22:21, 2 May 2011 (UTC)

Debate on climate effects
Another editor and I a going back and forth on commentary related to climate change and smart growth. Perhaps if a section on the purported connection were written in such a way as to denote a logical connection between the two, I would be aemnable to keeping it. As written, it has no connection, and appearst to be present more for political reasons than those related to the gathering of encyclopedic knowledge.

-CompassRose. — Preceding unsigned comment added by CompassRose65 (talk • contribs) 20:01, 30 June 2012 (UTC)

Stupid growth
Please note this essay from Harvard Divinity School by Timothy C. Weiskel - http://ecojustice.net/2005-ENVRE120/PDF/20020000-Smart-Growth-10-Commandments.pdf - "the consequences of "stupid" growth (mindless growth, aimless growth, anarchic growth) are now becoming too apparent to ignore". DAB (talk) 17:18, 7 August 2013 (UTC)

Dr. Weiskel created and directed of the Environmental Ethics & Public Policy Program at the Harvard Divinity School from 1989 to 1999, where he taught courses in environmental ethics and religious perspectives on the environment - http://ecoethics.net/hsev/2001-2002/TCW-Brief-Bio.htm 72.243.80.253 (talk) 17:45, 7 August 2013 (UTC)

German article
I'd love to create a German article on this topic. Anyone fluent in here who's up to support me? :) Cheers Horst-schlaemma (talk) 11:04, 23 March 2014 (UTC)

External links modified
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title: Talk:Smart growth


text:
C (musical note)

C or Do is the first note of the C major scale, the third note of the A minor scale (the relative minor of C major), and the fourth note (G, A, B, C) of the Guidonian hand, commonly pitched around 261.63 Hz. The actual frequency has depended on historical pitch standards, and for transposing instruments a distinction is made between written and sounding or concert pitch. It has enharmonic equivalents of B♯ and D𝄫.

In English the term Do is used interchangeably with C only in the context of fixed Do solfège; in the movable Do system Do refers to the tonic of the prevailing key.

Frequency
Historically, concert pitch has varied. For an instrument in equal temperament tuned to the A440 pitch standard widely adopted in 1939, middle C has a frequency around 261.63 Hz (for other notes see piano key frequencies). Scientific pitch was originally proposed in 1713 by French physicist Joseph Sauveur and based on the numerically convenient frequency of 256 Hz for middle C, all C's being powers of two. After the A440 pitch standard was adopted by musicians, the Acoustical Society of America published new frequency tables for scientific use. A movement to restore the older A435 standard has used the banners "Verdi tuning", "philosophical pitch" or the easily confused scientific pitch.

Middle C
Middle C (the fourth C key from left on a standard 88-key piano keyboard) is designated C4 in scientific pitch notation, c in Helmholtz pitch notation, and note number 60 in the MIDI standard.

While the expression middle C is generally clear across instruments and clefs, some musicians naturally use the term to refer to the C note in the middle of their specific instrument's range. C4 (approximately 261.626 Hz ) may be called Low C by someone playing a Western concert flute, which has a higher and narrower playing range than the piano, while C5 (523.251 Hz) would be middle C. This practice has led some to encourage standardizing on C4 as the definitive middle C in instructional materials across all instruments.

On the grand staff, middle C is notated with a ledger line above the top line of the bass staff or below the bottom line of the treble staff. Alternatively, it is written on the centre line of a staff using the alto clef, or on the fourth line from the bottom, or the second line from the top, of staves using the tenor clef.

Other octaves
In vocal music, the term High C (sometimes called Top C ) can refer to either the soprano's C6 (1046.502 Hz; in Helmholtz notation) or the tenor's C5; soprano written as the C two ledger lines above the treble clef, with the tenor voice the space above concert A, sung an octave lower. Sometimes written with “8v” below the treble, to represent the octave (8 tones in a major scale).

Tenor C is an organ builder's term for small C or C3 (130.813 Hz), the note one octave below middle C. In older stoplists it usually means that a rank was not yet full compass, omitting the bottom octave, until that octave was added later on.

Common scales beginning on C

 * C major: C D E F G A B C′
 * C natural minor: C D E♭ F G A♭ B♭ C′
 * C harmonic minor: C D E♭ F G A♭ B C′
 * C melodic minor ascending: C D E♭ F G A B C′
 * C melodic minor descending: C′ B♭ A♭ G F E♭ D C

Diatonic scales

 * C Ionian: C D E F G A B C′
 * C Dorian: C D E♭ F G A B♭ C′
 * C Phrygian: C D♭ E♭ F G A♭ B♭ C′
 * C Lydian: C D E F♯ G A B C′
 * C Mixolydian: C D E F G A B♭ C′
 * C Aeolian: C D E♭ F G A♭ B♭ C′
 * C Locrian: C D♭ E♭ F G♭ A♭ B♭ C′

Jazz melodic minor

 * C ascending melodic minor: C D E♭ F G A B C′
 * C Dorian ♭2: C D♭ E♭ F G A B♭ C′
 * C Lydian augmented: C D E F♯ G♯ A B C′
 * C Lydian dominant: C D E F♯ G A B♭ C′
 * C Mixolydian ♭6: C D E F G A♭ B♭ C′
 * C Locrian ♮2: C D E♭ F G♭ A♭ B♭ C′
 * C altered: C D♭ E♭ F♭ G♭ A♭ B♭ C′

title: C (musical note)


text:
Staff (music)

In Western musical notation, the staff (UK also stave; plural: staffs or staves), also occasionally referred to as a pentagram,   is a set of five horizontal lines and four spaces that each represent a different musical pitch or in the case of a percussion staff, different percussion instruments. Appropriate music symbols, depending on the intended effect, are placed on the staff according to their corresponding pitch or function. Musical notes are placed by pitch, percussion notes are placed by instrument, and rests and other symbols are placed by convention.

The absolute pitch of each line of a non-percussive staff is indicated by the placement of a clef symbol at the appropriate vertical position on the left-hand side of the staff (possibly modified by conventions for specific instruments). For example, the treble clef, also known as the G clef, is placed on the second line (counting upward), fixing that line as the pitch first G above "middle C".

The lines and spaces are numbered from bottom to top; the bottom line is the first line and the top line is the fifth line.

The musical staff is analogous to a mathematical graph of pitch with respect to time. Pitches of notes are given by their vertical position on the staff and notes are played from left to right. Unlike a graph, however, the number of semitones represented by a vertical step from a line to an adjacent space depends on the key, and the exact timing of the beginning of each note is not directly proportional to its horizontal position; rather, exact timing is encoded by the musical symbol chosen for each note in addition to the tempo.

A time signature to the right of the clef indicates the relationship between timing counts and note symbols, while bar lines group notes on the staff into measures.

Usage and etymology
Staff is more common than stave in both American English and British English, with the latter being, in fact, a back-formation from the plural staves. The plural staffs also exists for staff in both American and British English, alongside the traditional plural staves. In addition to the pronunciations expected from the spellings, both plural forms are also pronounced in American English.

Staff positions
The vertical position of the notehead on the staff indicates which note to play: higher-pitched notes are marked higher on the staff. The notehead can be placed with its center intersecting a line (on a line) or in between the lines touching the lines above and below (in a space). Notes outside the range of the staff are placed on or between ledger lines—lines the width of the note they need to hold—added above or below the staff.

Which staff positions represent which notes is determined by a clef placed at the beginning of the staff. The clef identifies a particular line as a specific note, and all other notes are determined relative to that line. For example, the treble clef puts the G above middle C on the second line. The interval between adjacent staff positions is one step in the diatonic scale. Once fixed by a clef, the notes represented by the positions on the staff can be modified by the key signature or accidentals on individual notes. A clefless staff may be used to represent a set of percussion sounds; each line typically represents a different instrument.

Ensemble staves
A vertical line drawn to the left of multiple staves creates a system, indicating that the music on all the staves is to be played simultaneously. A brace (curly bracket) is used to join multiple staves that represent an instrument, such as a piano, organ, harp, or marimba. A bracket is an additional vertical line joining staves to show groupings of instruments that function as a unit, such as the string section of an orchestra. Sometimes a second bracket is used to show instruments grouped in pairs, such as the first and second oboes or first and second violins in an orchestra. In some cases, a brace is used for this purpose.

When more than one system appears on a page, often two parallel diagonal strokes are placed on the left side of the score to separate them.

Four-part SATB vocal settings, especially in hymnals, use a divisi notation on a two-staff system with soprano and alto voices sharing the upper staff and tenor and bass voices on the lower staff.

Confusingly, the German System (often in the combined forms Liniensystem or Notensystem) may refer to a single staff as well as to the Akkolade (from the French) or system in the English sense; the Italian term is accollatura.

 Grand staff
When music on two staves is joined by a brace, or is intended to be played at once by a single performer (usually a keyboard instrument or harp), a grand staff (American English) or great stave (British English) is created. Typically, the upper staff uses a treble clef and the lower staff has a bass clef. In this instance, middle C is centered between the two staffs, and it can be written on the first ledger line below the upper staff or the first ledger line above the lower staff. Very rarely, a centered line with a small C clef is written, and usually used to indicate that B, C, or D on the line can be played with either hand (ledger lines are not used from a center alto as this creates confusion). When playing the piano or harp, the upper staff is normally played with the right hand and the lower staff with the left hand. In music intended for organ with pedalboard, a grand staff normally comprises three staves, one for each hand on the manuals and one for the feet on the pedalboard.

History
Early Western medieval notation was written with neumes, which did not specify exact pitches but only the shape of the melodies, i.e. indicating when the musical line went up or down; presumably these were intended as mnemonics for melodies which had been taught by rote.

During the 9th through 11th centuries a number of systems were developed to specify pitch more precisely, including diastematic neumes whose height on the page corresponded with their absolute pitch level (Longobardian and Beneventan manuscripts from Italy show this technique around the year 1000). Digraphic notation, using letter names similar to modern note names in conjunction with the neumes, made a brief appearance in a few manuscripts, but a number of manuscripts used one or more horizontal lines to indicate particular pitches.

The treatise Musica enchiriadis (c. 900) uses Daseian notation for indicating specific pitches, but the modern use of staff lines is attributed to Guido d'Arezzo (990–1050), whose four-line staff is still used (though without the red and yellow coloring he recommended) in Gregorian chant publications today. Five-line staves appeared in Italy in the 13th century and it was promoted by Ugolino da Forlì; staves with four, five, and six lines were used as late as 1600.

title: Staff (music)