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Charge-coupled device

A charge-coupled device (CCD) is an integrated circuit containing an array of linked, or coupled, capacitors. Under the control of an external circuit, each capacitor can transfer its electric charge to a neighboring capacitor. CCD sensors are a major technology used in digital imaging.

Overview
In a CCD image sensor, pixels are represented by p-doped metal–oxide–semiconductor (MOS) capacitors. These MOS capacitors, the basic building blocks of a CCD, are biased above the threshold for inversion when image acquisition begins, allowing the conversion of incoming photons into electron charges at the semiconductor-oxide interface; the CCD is then used to read out these charges.

Although CCDs are not the only technology to allow for light detection, CCD image sensors are widely used in professional, medical, and scientific applications where high-quality image data are required.

In applications with less exacting quality demands, such as consumer and professional digital cameras, active pixel sensors, also known as CMOS sensors (complementary MOS sensors), are generally used.

However, the large quality advantage CCDs enjoyed early on has narrowed over time and since the late 2010s CMOS sensors are the dominant technology, having largely if not completely replaced CCD image sensors.

History
The basis for the CCD is the metal–oxide–semiconductor (MOS) structure, with MOS capacitors being the basic building blocks of a CCD, and a depleted MOS structure used as the photodetector in early CCD devices.

In the late 1960s, Willard Boyle and George E. Smith at Bell Labs were researching MOS technology while working on semiconductor bubble memory. They realized that an electric charge was the analogy of the magnetic bubble and that it could be stored on a tiny MOS capacitor. As it was fairly straightforward to fabricate a series of MOS capacitors in a row, they connected a suitable voltage to them so that the charge could be stepped along from one to the next. This led to the invention of the charge-coupled device by Boyle and Smith in 1969. They conceived of the design of what they termed, in their notebook, "Charge 'Bubble' Devices".

The initial paper describing the concept in April 1970 listed possible uses as memory, a delay line, and an imaging device. The device could also be used as a shift register. The essence of the design was the ability to transfer charge along the surface of a semiconductor from one storage capacitor to the next. The concept was similar in principle to the bucket-brigade device (BBD), which was developed at Philips Research Labs during the late 1960s.

The first experimental device demonstrating the principle was a row of closely spaced metal squares on an oxidized silicon surface electrically accessed by wire bonds. It was demonstrated by Gil Amelio, Michael Francis Tompsett and George Smith in April 1970. This was the first experimental application of the CCD in image sensor technology, and used a depleted MOS structure as the photodetector. The first patent on the application of CCDs to imaging was assigned to Tompsett, who filed the application in 1971.

The first working CCD made with integrated circuit technology was a simple 8-bit shift register, reported by Tompsett, Amelio and Smith in August 1970. This device had input and output circuits and was used to demonstrate its use as a shift register and as a crude eight pixel linear imaging device. Development of the device progressed at a rapid rate. By 1971, Bell researchers led by Michael Tompsett were able to capture images with simple linear devices. Several companies, including Fairchild Semiconductor, RCA and Texas Instruments, picked up on the invention and began development programs. Fairchild's effort, led by ex-Bell researcher Gil Amelio, was the first with commercial devices, and by 1974 had a linear 500-element device and a 2D 100 × 100 pixel device. Peter Dillon, a scientist at Kodak Research Labs, invented the first color CCD image sensor by overlaying a color filter array on this Fairchild 100 x 100 pixel Interline CCD starting in 1974. Steven Sasson, an electrical engineer working for the Kodak Apparatus Division, invented a digital still camera using this same Fairchild 100 × 100 CCD in 1975.

The interline transfer (ILT) CCD device was proposed by L. Walsh and R. Dyck at Fairchild in 1973 to reduce smear and eliminate a mechanical shutter. To further reduce smear from bright light sources, the frame-interline-transfer (FIT) CCD architecture was developed by K. Horii, T. Kuroda and T. Kunii at Matsushita (now Panasonic) in 1981.

The first KH-11 KENNEN reconnaissance satellite equipped with charge-coupled device array (800 × 800 pixels) technology for imaging was launched in December 1976. Under the leadership of Kazuo Iwama, Sony started a large development effort on CCDs involving a significant investment. Eventually, Sony managed to mass-produce CCDs for their camcorders. Before this happened, Iwama died in August 1982. Subsequently a CCD chip was placed on his tombstone to acknowledge his contribution. The first mass-produced consumer CCD video camera, the CCD-G5, was released by Sony in 1983, based on a prototype developed by Yoshiaki Hagiwara in 1981.

Early CCD sensors suffered from shutter lag. This was largely resolved with the invention of the pinned photodiode (PPD). It was invented by Nobukazu Teranishi, Hiromitsu Shiraki and Yasuo Ishihara at NEC in 1980. They recognized that lag can be eliminated if the signal carriers could be transferred from the photodiode to the CCD. This led to their invention of the pinned photodiode, a photodetector structure with low lag, low noise, high quantum efficiency and low dark current. It was first publicly reported by Teranishi and Ishihara with A. Kohono, E. Oda and K. Arai in 1982, with the addition of an anti-blooming structure. The new photodetector structure invented at NEC was given the name "pinned photodiode" (PPD) by B.C. Burkey at Kodak in 1984. In 1987, the PPD began to be incorporated into most CCD devices, becoming a fixture in consumer electronic video cameras and then digital still cameras. Since then, the PPD has been used in nearly all CCD sensors and then CMOS sensors.

In January 2006, Boyle and Smith were awarded the National Academy of Engineering Charles Stark Draper Prize, and in 2009 they were awarded the Nobel Prize for Physics for their invention of the CCD concept. Michael Tompsett was awarded the 2010 National Medal of Technology and Innovation, for pioneering work and electronic technologies including the design and development of the first CCD imagers. He was also awarded the 2012 IEEE Edison Medal for "pioneering contributions to imaging devices including CCD Imagers, cameras and thermal imagers".

Basics of operation
In a CCD for capturing images, there is a photoactive region (an epitaxial layer of silicon), and a transmission region made out of a shift register (the CCD, properly speaking).

An image is projected through a lens onto the capacitor array (the photoactive region), causing each capacitor to accumulate an electric charge proportional to the light intensity at that location. A one-dimensional array, used in line-scan cameras, captures a single slice of the image, whereas a two-dimensional array, used in video and still cameras, captures a two-dimensional picture corresponding to the scene projected onto the focal plane of the sensor. Once the array has been exposed to the image, a control circuit causes each capacitor to transfer its contents to its neighbor (operating as a shift register). The last capacitor in the array dumps its charge into a charge amplifier, which converts the charge into a voltage. By repeating this process, the controlling circuit converts the entire contents of the array in the semiconductor to a sequence of voltages. In a digital device, these voltages are then sampled, digitized, and usually stored in memory; in an analog device (such as an analog video camera), they are processed into a continuous analog signal (e.g. by feeding the output of the charge amplifier into a low-pass filter), which is then processed and fed out to other circuits for transmission, recording, or other processing.

Charge generation
Before the MOS capacitors are exposed to light, they are biased into the depletion region; in n-channel CCDs, the silicon under the bias gate is slightly p-doped or intrinsic. The gate is then biased at a positive potential, above the threshold for strong inversion, which will eventually result in the creation of an n channel below the gate as in a MOSFET. However, it takes time to reach this thermal equilibrium: up to hours in high-end scientific cameras cooled at low temperature. Initially after biasing, the holes are pushed far into the substrate, and no mobile electrons are at or near the surface; the CCD thus operates in a non-equilibrium state called deep depletion. Then, when electron–hole pairs are generated in the depletion region, they are separated by the electric field, the electrons move toward the surface, and the holes move toward the substrate. Four pair-generation processes can be identified:
 * photo-generation (up to 95% of quantum efficiency),
 * generation in the depletion region,
 * generation at the surface, and
 * generation in the neutral bulk.

The last three processes are known as dark-current generation, and add noise to the image; they can limit the total usable integration time. The accumulation of electrons at or near the surface can proceed either until image integration is over and charge begins to be transferred, or thermal equilibrium is reached. In this case, the well is said to be full. The maximum capacity of each well is known as the well depth, typically about 105 electrons per pixel. CCDs are normally susceptible to ionizing radiation and energetic particles which causes noise in the output of the CCD, and this must be taken into consideration in satellites using CCDs.

Design and manufacturing
The photoactive region of a CCD is, generally, an epitaxial layer of silicon. It is lightly p doped (usually with boron) and is grown upon a substrate material, often p++. In buried-channel devices, the type of design utilized in most modern CCDs, certain areas of the surface of the silicon are ion implanted with phosphorus, giving them an n-doped designation. This region defines the channel in which the photogenerated charge packets will travel. Simon Sze details the advantages of a buried-channel device: "This thin layer (= 0.2–0.3 micron) is fully depleted and the accumulated photogenerated charge is kept away from the surface. This structure has the advantages of higher transfer efficiency and lower dark current, from reduced surface recombination. The penalty is smaller charge capacity, by a factor of 2–3 compared to the surface-channel CCD." The gate oxide, i.e. the capacitor dielectric, is grown on top of the epitaxial layer and substrate.

Later in the process, polysilicon gates are deposited by chemical vapor deposition, patterned with photolithography, and etched in such a way that the separately phased gates lie perpendicular to the channels. The channels are further defined by utilization of the LOCOS process to produce the channel stop region.

Channel stops are thermally grown oxides that serve to isolate the charge packets in one column from those in another. These channel stops are produced before the polysilicon gates are, as the LOCOS process utilizes a high-temperature step that would destroy the gate material. The channel stops are parallel to, and exclusive of, the channel, or "charge carrying", regions.

Channel stops often have a p+ doped region underlying them, providing a further barrier to the electrons in the charge packets (this discussion of the physics of CCD devices assumes an electron transfer device, though hole transfer is possible).

The clocking of the gates, alternately high and low, will forward and reverse bias the diode that is provided by the buried channel (n-doped) and the epitaxial layer (p-doped). This will cause the CCD to deplete, near the p–n junction and will collect and move the charge packets beneath the gates—and within the channels—of the device.

CCD manufacturing and operation can be optimized for different uses. The above process describes a frame transfer CCD. While CCDs may be manufactured on a heavily doped p++ wafer it is also possible to manufacture a device inside p-wells that have been placed on an n-wafer. This second method, reportedly, reduces smear, dark current, and infrared and red response. This method of manufacture is used in the construction of interline-transfer devices.

Another version of CCD is called a peristaltic CCD. In a peristaltic charge-coupled device, the charge-packet transfer operation is analogous to the peristaltic contraction and dilation of the digestive system. The peristaltic CCD has an additional implant that keeps the charge away from the silicon/silicon dioxide interface and generates a large lateral electric field from one gate to the next. This provides an additional driving force to aid in transfer of the charge packets.

Architecture
The CCD image sensors can be implemented in several different architectures. The most common are full-frame, frame-transfer, and interline. The distinguishing characteristic of each of these architectures is their approach to the problem of shuttering.

In a full-frame device, all of the image area is active, and there is no electronic shutter. A mechanical shutter must be added to this type of sensor or the image smears as the device is clocked or read out.

With a frame-transfer CCD, half of the silicon area is covered by an opaque mask (typically aluminum). The image can be quickly transferred from the image area to the opaque area or storage region with acceptable smear of a few percent. That image can then be read out slowly from the storage region while a new image is integrating or exposing in the active area. Frame-transfer devices typically do not require a mechanical shutter and were a common architecture for early solid-state broadcast cameras. The downside to the frame-transfer architecture is that it requires twice the silicon real estate of an equivalent full-frame device; hence, it costs roughly twice as much.

The interline architecture extends this concept one step further and masks every other column of the image sensor for storage. In this device, only one pixel shift has to occur to transfer from image area to storage area; thus, shutter times can be less than a microsecond and smear is essentially eliminated. The advantage is not free, however, as the imaging area is now covered by opaque strips dropping the fill factor to approximately 50 percent and the effective quantum efficiency by an equivalent amount. Modern designs have addressed this deleterious characteristic by adding microlenses on the surface of the device to direct light away from the opaque regions and on the active area. Microlenses can bring the fill factor back up to 90 percent or more depending on pixel size and the overall system's optical design.

The choice of architecture comes down to one of utility. If the application cannot tolerate an expensive, failure-prone, power-intensive mechanical shutter, an interline device is the right choice. Consumer snap-shot cameras have used interline devices. On the other hand, for those applications that require the best possible light collection and issues of money, power and time are less important, the full-frame device is the right choice. Astronomers tend to prefer full-frame devices. The frame-transfer falls in between and was a common choice before the fill-factor issue of interline devices was addressed. Today, frame-transfer is usually chosen when an interline architecture is not available, such as in a back-illuminated device.

CCDs containing grids of pixels are used in digital cameras, optical scanners, and video cameras as light-sensing devices. They commonly respond to 70 percent of the incident light (meaning a quantum efficiency of about 70 percent) making them far more efficient than photographic film, which captures only about 2 percent of the incident light.

Most common types of CCDs are sensitive to near-infrared light, which allows infrared photography, night-vision devices, and zero lux (or near zero lux) video-recording/photography. For normal silicon-based detectors, the sensitivity is limited to 1.1 μm. One other consequence of their sensitivity to infrared is that infrared from remote controls often appears on CCD-based digital cameras or camcorders if they do not have infrared blockers.

Cooling reduces the array's dark current, improving the sensitivity of the CCD to low light intensities, even for ultraviolet and visible wavelengths. Professional observatories often cool their detectors with liquid nitrogen to reduce the dark current, and therefore the thermal noise, to negligible levels.

Frame transfer CCD

The frame transfer CCD imager was the first imaging structure proposed for CCD Imaging by Michael Tompsett at Bell Laboratories. A frame transfer CCD is a specialized CCD, often used in astronomy and some professional video cameras, designed for high exposure efficiency and correctness.

The normal functioning of a CCD, astronomical or otherwise, can be divided into two phases: exposure and readout. During the first phase, the CCD passively collects incoming photons, storing electrons in its cells. After the exposure time is passed, the cells are read out one line at a time. During the readout phase, cells are shifted down the entire area of the CCD. While they are shifted, they continue to collect light. Thus, if the shifting is not fast enough, errors can result from light that falls on a cell holding charge during the transfer. These errors are referred to as "vertical smear" and cause a strong light source to create a vertical line above and below its exact location. In addition, the CCD cannot be used to collect light while it is being read out. A faster shifting requires a faster readout, and a faster readout can introduce errors in the cell charge measurement, leading to a higher noise level.

A frame transfer CCD solves both problems: it has a shielded, not light sensitive, area containing as many cells as the area exposed to light. Typically, this area is covered by a reflective material such as aluminium. When the exposure time is up, the cells are transferred very rapidly to the hidden area. Here, safe from any incoming light, cells can be read out at any speed one deems necessary to correctly measure the cells' charge. At the same time, the exposed part of the CCD is collecting light again, so no delay occurs between successive exposures.

The disadvantage of such a CCD is the higher cost: the cell area is basically doubled, and more complex control electronics are needed.

Intensified charge-coupled device
An intensified charge-coupled device (ICCD) is a CCD that is optically connected to an image intensifier that is mounted in front of the CCD.

An image intensifier includes three functional elements: a photocathode, a micro-channel plate (MCP) and a phosphor screen. These three elements are mounted one close behind the other in the mentioned sequence. The photons which are coming from the light source fall onto the photocathode, thereby generating photoelectrons. The photoelectrons are accelerated towards the MCP by an electrical control voltage, applied between photocathode and MCP. The electrons are multiplied inside of the MCP and thereafter accelerated towards the phosphor screen. The phosphor screen finally converts the multiplied electrons back to photons which are guided to the CCD by a fiber optic or a lens.

An image intensifier inherently includes a shutter functionality: If the control voltage between the photocathode and the MCP is reversed, the emitted photoelectrons are not accelerated towards the MCP but return to the photocathode. Thus, no electrons are multiplied and emitted by the MCP, no electrons are going to the phosphor screen and no light is emitted from the image intensifier. In this case no light falls onto the CCD, which means that the shutter is closed. The process of reversing the control voltage at the photocathode is called gating and therefore ICCDs are also called gateable CCD cameras.

Besides the extremely high sensitivity of ICCD cameras, which enable single photon detection, the gateability is one of the major advantages of the ICCD over the EMCCD cameras. The highest performing ICCD cameras enable shutter times as short as 200 picoseconds.

ICCD cameras are in general somewhat higher in price than EMCCD cameras because they need the expensive image intensifier. On the other hand, EMCCD cameras need a cooling system to cool the EMCCD chip down to temperatures around 170 K. This cooling system adds additional costs to the EMCCD camera and often yields heavy condensation problems in the application.

ICCDs are used in night vision devices and in various scientific applications.

Electron-multiplying CCD

An electron-multiplying CCD (EMCCD, also known as an L3Vision CCD, a product commercialized by e2v Ltd., GB, L3CCD or Impactron CCD, a now-discontinued product offered in the past by Texas Instruments) is a charge-coupled device in which a gain register is placed between the shift register and the output amplifier. The gain register is split up into a large number of stages. In each stage, the electrons are multiplied by impact ionization in a similar way to an avalanche diode. The gain probability at every stage of the register is small (P < 2%), but as the number of elements is large (N > 500), the overall gain can be very high ($$g = (1 + P)^N$$), with single input electrons giving many thousands of output electrons. Reading a signal from a CCD gives a noise background, typically a few electrons. In an EMCCD, this noise is superimposed on many thousands of electrons rather than a single electron; the devices' primary advantage is thus their negligible readout noise. The use of avalanche breakdown for amplification of photo charges had already been described in the in 1973 by George E. Smith/Bell Telephone Laboratories.

EMCCDs show a similar sensitivity to intensified CCDs (ICCDs). However, as with ICCDs, the gain that is applied in the gain register is stochastic and the exact gain that has been applied to a pixel's charge is impossible to know. At high gains (> 30), this uncertainty has the same effect on the signal-to-noise ratio (SNR) as halving the quantum efficiency (QE) with respect to operation with a gain of unity. This effect is referred to as the Excess Noise Factor (ENF). However, at very low light levels (where the quantum efficiency is most important), it can be assumed that a pixel either contains an electron—or not. This removes the noise associated with the stochastic multiplication at the risk of counting multiple electrons in the same pixel as a single electron. To avoid multiple counts in one pixel due to coincident photons in this mode of operation, high frame rates are essential. The dispersion in the gain is shown in the graph on the right. For multiplication registers with many elements and large gains it is well modelled by the equation:

$$P\left (n \right ) = \frac{\left (n-m+1\right )^{m-1}}{\left (m-1 \right )!\left (g-1+\frac{1}{m}\right )^{m}}\exp \left ( - \frac{n-m+1}{g-1+\frac{1}{m}}\right ) \quad \text{ if } n \ge m $$ where P is the probability of getting n output electrons given m input electrons and a total mean multiplication register gain of g. For very large numbers of input electrons, this complex distribution function converges towards a Gaussian.

Because of the lower costs and better resolution, EMCCDs are capable of replacing ICCDs in many applications. ICCDs still have the advantage that they can be gated very fast and thus are useful in applications like range-gated imaging. EMCCD cameras indispensably need a cooling system—using either thermoelectric cooling or liquid nitrogen—to cool the chip down to temperatures in the range of -65 to -95 C. This cooling system adds additional costs to the EMCCD imaging system and may yield condensation problems in the application. However, high-end EMCCD cameras are equipped with a permanent hermetic vacuum system confining the chip to avoid condensation issues.

The low-light capabilities of EMCCDs find use in astronomy and biomedical research, among other fields. In particular, their low noise at high readout speeds makes them very useful for a variety of astronomical applications involving low light sources and transient events such as lucky imaging of faint stars, high speed photon counting photometry, Fabry-Pérot spectroscopy and high-resolution spectroscopy. More recently, these types of CCDs have broken into the field of biomedical research in low-light applications including small animal imaging, single-molecule imaging, Raman spectroscopy, super resolution microscopy as well as a wide variety of modern fluorescence microscopy techniques thanks to greater SNR in low-light conditions in comparison with traditional CCDs and ICCDs.

In terms of noise, commercial EMCCD cameras typically have clock-induced charge (CIC) and dark current (dependent on the extent of cooling) that together lead to an effective readout noise ranging from 0.01 to 1 electrons per pixel read. However, recent improvements in EMCCD technology have led to a new generation of cameras capable of producing significantly less CIC, higher charge transfer efficiency and an EM gain 5 times higher than what was previously available. These advances in low-light detection lead to an effective total background noise of 0.001 electrons per pixel read, a noise floor unmatched by any other low-light imaging device.

Use in astronomy
Due to the high quantum efficiencies of charge-coupled device (CCD) (the ideal quantum efficiency is 100%, one generated electron per incident photon), linearity of their outputs, ease of use compared to photographic plates, and a variety of other reasons, CCDs were very rapidly adopted by astronomers for nearly all UV-to-infrared applications.

Thermal noise and cosmic rays may alter the pixels in the CCD array. To counter such effects, astronomers take several exposures with the CCD shutter closed and opened. The average of images taken with the shutter closed is necessary to lower the random noise. Once developed, the dark frame average image is then subtracted from the open-shutter image to remove the dark current and other systematic defects (dead pixels, hot pixels, etc.) in the CCD. Newer Skipper CCDs counter noise by collecting data with the same collected charge multiple times and has applications in precision light Dark Matter searches and neutrino measurements.

The Hubble Space Telescope, in particular, has a highly developed series of steps ("data reduction pipeline") to convert the raw CCD data to useful images.

CCD cameras used in astrophotography often require sturdy mounts to cope with vibrations from wind and other sources, along with the tremendous weight of most imaging platforms. To take long exposures of galaxies and nebulae, many astronomers use a technique known as auto-guiding. Most autoguiders use a second CCD chip to monitor deviations during imaging. This chip can rapidly detect errors in tracking and command the mount motors to correct for them.

An unusual astronomical application of CCDs, called drift-scanning, uses a CCD to make a fixed telescope behave like a tracking telescope and follow the motion of the sky. The charges in the CCD are transferred and read in a direction parallel to the motion of the sky, and at the same speed. In this way, the telescope can image a larger region of the sky than its normal field of view. The Sloan Digital Sky Survey is the most famous example of this, using the technique to produce a survey of over a quarter of the sky. The Gaia space telescope is another instrument operating in this mode, rotating about its axis at a constant rate of 1 revolution in 6 hours and scanning a 360° by 0.5° strip on the sky during this time; a star traverses the entire focal plane in about 40 seconds (effective exposure time).

In addition to imagers, CCDs are also used in an array of analytical instrumentation including spectrometers and interferometers.

Color cameras

Digital color cameras, including the digital color cameras in smartphones, generally use a integral color image sensor, which has a color filter array fabricated on top of the monochrome pixels of the CCD. The most popular CFA pattern is known as the Bayer filter, which is named for its inventor, Kodak scientist Bryce Bayer. In the Bayer pattern, each square of four pixels has one filtered red, one blue, and two green pixels (the human eye has greater acuity for luminance, which is more heavily weighted in green than in either red or blue). As a result, the luminance information is collected in each row and column using a checkerboard pattern, and the color resolution is lower than the luminance resolution.

Better color separation can be reached by three-CCD devices (3CCD) and a dichroic beam splitter prism, that splits the image into red, green and blue components. Each of the three CCDs is arranged to respond to a particular color. Many professional video camcorders, and some semi-professional camcorders, use this technique, although developments in competing CMOS technology have made CMOS sensors, both with beam-splitters and Bayer filters, increasingly popular in high-end video and digital cinema cameras. Another advantage of 3CCD over a Bayer mask device is higher quantum efficiency (higher light sensitivity), because most of the light from the lens enters one of the silicon sensors, while a Bayer mask absorbs a high proportion (more than 2/3) of the light falling on each pixel location.

For still scenes, for instance in microscopy, the resolution of a Bayer mask device can be enhanced by microscanning technology. During the process of color co-site sampling, several frames of the scene are produced. Between acquisitions, the sensor is moved in pixel dimensions, so that each point in the visual field is acquired consecutively by elements of the mask that are sensitive to the red, green, and blue components of its color. Eventually every pixel in the image has been scanned at least once in each color and the resolution of the three channels become equivalent (the resolutions of red and blue channels are quadrupled while the green channel is doubled).

Sensor sizes
Sensors (CCD / CMOS) come in various sizes, or image sensor formats. These sizes are often referred to with an inch fraction designation such as 1/1.8″ or 2/3″ called the optical format. This measurement originates back in the 1950s and the time of Vidicon tubes.

Blooming
When a CCD exposure is long enough, eventually the electrons that collect in the "bins" in the brightest part of the image will overflow the bin, resulting in blooming. The structure of the CCD allows the electrons to flow more easily in one direction than another, resulting in vertical streaking.

Some anti-blooming features that can be built into a CCD reduce its sensitivity to light by using some of the pixel area for a drain structure. James M. Early developed a vertical anti-blooming drain that would not detract from the light collection area, and so did not reduce light sensitivity.

title: Charge-coupled device


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Computer memory

Computer memory stores information, such as data and programs, for immediate use in the computer. The term memory is often synonymous with the terms RAM, main memory, or primary storage. Archaic synonyms for main memory include core (for magnetic core memory) and store.

Main memory operates at a high speed compared to mass storage which is slower but less expensive per bit and higher in capacity. Besides storing opened programs and data being actively processed, computer memory serves as a mass storage cache and write buffer to improve both reading and writing performance. Operating systems borrow RAM capacity for caching so long as not needed by running software. If needed, contents of the computer memory can be transferred to storage; a common way of doing this is through a memory management technique called virtual memory.

Modern computer memory is implemented as semiconductor memory, where data is stored within memory cells built from MOS transistors and other components on an integrated circuit. There are two main kinds of semiconductor memory: volatile and non-volatile. Examples of non-volatile memory are flash memory and ROM, PROM, EPROM, and EEPROM memory. Examples of volatile memory are dynamic random-access memory (DRAM) used for primary storage and static random-access memory (SRAM) used mainly for CPU cache.

Most semiconductor memory is organized into memory cells each storing one bit (0 or 1). Flash memory organization includes both one bit per memory cell and a multi-level cell capable of storing multiple bits per cell. The memory cells are grouped into words of fixed word length, for example, 1, 2, 4, 8, 16, 32, 64 or 128 bits. Each word can be accessed by a binary address of N bits, making it possible to store 2N words in the memory.

History

In the early 1940s, memory technology often permitted a capacity of a few bytes. The first electronic programmable digital computer, the ENIAC, using thousands of vacuum tubes, could perform simple calculations involving 20 numbers of ten decimal digits stored in the vacuum tubes.

The next significant advance in computer memory came with acoustic delay-line memory, developed by J. Presper Eckert in the early 1940s. Through the construction of a glass tube filled with mercury and plugged at each end with a quartz crystal, delay lines could store bits of information in the form of sound waves propagating through the mercury, with the quartz crystals acting as transducers to read and write bits. Delay-line memory was limited to a capacity of up to a few thousand bits.

Two alternatives to the delay line, the Williams tube and Selectron tube, originated in 1946, both using electron beams in glass tubes as means of storage. Using cathode-ray tubes, Fred Williams invented the Williams tube, which was the first random-access computer memory. The Williams tube was able to store more information than the Selectron tube (the Selectron was limited to 256 bits, while the Williams tube could store thousands) and was less expensive. The Williams tube was nevertheless frustratingly sensitive to environmental disturbances.

Efforts began in the late 1940s to find non-volatile memory. Magnetic-core memory allowed for recall of memory after power loss. It was developed by Frederick W. Viehe and An Wang in the late 1940s, and improved by Jay Forrester and Jan A. Rajchman in the early 1950s, before being commercialized with the Whirlwind I computer in 1953. Magnetic-core memory was the dominant form of memory until the development of MOS semiconductor memory in the 1960s.

The first semiconductor memory was implemented as a flip-flop circuit in the early 1960s using bipolar transistors. Semiconductor memory made from discrete devices was first shipped by Texas Instruments to the United States Air Force in 1961. The same year, the concept of solid-state memory on an integrated circuit (IC) chip was proposed by applications engineer Bob Norman at Fairchild Semiconductor. The first bipolar semiconductor memory IC chip was the SP95 introduced by IBM in 1965. While semiconductor memory offered improved performance over magnetic-core memory, it remain larger and more expensive and did not displace magnetic-core memory until the late 1960s.

MOS memory
The invention of the metal–oxide–semiconductor field-effect transistor (MOSFET) enabled the practical use of metal–oxide–semiconductor (MOS) transistors as memory cell storage elements. MOS memory was developed by John Schmidt at Fairchild Semiconductor in 1964. In addition to higher performance, MOS semiconductor memory was cheaper and consumed less power than magnetic core memory. In 1965, J. Wood and R. Ball of the Royal Radar Establishment proposed digital storage systems that use CMOS (complementary MOS) memory cells, in addition to MOSFET power devices for the power supply, switched cross-coupling, switches and delay-line storage. The development of silicon-gate MOS integrated circuit (MOS IC) technology by Federico Faggin at Fairchild in 1968 enabled the production of MOS memory chips. NMOS memory was commercialized by IBM in the early 1970s. MOS memory overtook magnetic core memory as the dominant memory technology in the early 1970s.

The two main types of volatile random-access memory (RAM) are static random-access memory (SRAM) and dynamic random-access memory (DRAM). Bipolar SRAM was invented by Robert Norman at Fairchild Semiconductor in 1963, followed by the development of MOS SRAM by John Schmidt at Fairchild in 1964. SRAM became an alternative to magnetic-core memory, but requires six transistors for each bit of data. Commercial use of SRAM began in 1965, when IBM introduced their SP95 SRAM chip for the System/360 Model 95.

Toshiba introduced bipolar DRAM memory cells for its Toscal BC-1411 electronic calculator in 1965. While it offered improved performance, bipolar DRAM could not compete with the lower price of the then dominant magnetic-core memory. MOS technology is the basis for modern DRAM. In 1966, Robert H. Dennard at the IBM Thomas J. Watson Research Center was working on MOS memory. While examining the characteristics of MOS technology, he found it was possible to build capacitors, and that storing a charge or no charge on the MOS capacitor could represent the 1 and 0 of a bit, while the MOS transistor could control writing the charge to the capacitor. This led to his development of a single-transistor DRAM memory cell. In 1967, Dennard filed a patent for a single-transistor DRAM memory cell based on MOS technology. This led to the first commercial DRAM IC chip, the Intel 1103 in October 1970. Synchronous dynamic random-access memory (SDRAM) later debuted with the Samsung KM48SL2000 chip in 1992.

The term memory is also often used to refer to non-volatile memory including read-only memory (ROM) through modern flash memory. Programmable read-only memory (PROM) was invented by Wen Tsing Chow in 1956, while working for the Arma Division of the American Bosch Arma Corporation. In 1967, Dawon Kahng and Simon Sze of Bell Labs proposed that the floating gate of a MOS semiconductor device could be used for the cell of a reprogrammable ROM, which led to Dov Frohman of Intel inventing EPROM (erasable PROM) in 1971. EEPROM (electrically erasable PROM) was developed by Yasuo Tarui, Yutaka Hayashi and Kiyoko Naga at the Electrotechnical Laboratory in 1972. Flash memory was invented by Fujio Masuoka at Toshiba in the early 1980s. Masuoka and colleagues presented the invention of NOR flash in 1984, and then NAND flash in 1987. Toshiba commercialized NAND flash memory in 1987.

Developments in technology and economies of scale have made possible so-called very large memory (VLM) computers.

Volatile memory

Volatile memory is computer memory that requires power to maintain the stored information. Most modern semiconductor volatile memory is either static RAM (SRAM) or dynamic RAM (DRAM). DRAM dominates for desktop system memory. SRAM is used for CPU cache. SRAM is also found in small embedded systems requiring little memory.

SRAM retains its contents as long as the power is connected and may use a simpler interface, but commonly uses six transistors per bit. Dynamic RAM is more complicated for interfacing and control, needing regular refresh cycles to prevent losing its contents, but uses only one transistor and one capacitor per bit, allowing it to reach much higher densities and much cheaper per-bit costs.

Non-volatile memory
Non-volatile memory can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, most types of magnetic computer storage devices (e.g. hard disk drives, floppy disks and magnetic tape), optical discs, and early computer storage methods such as magnetic drum, paper tape and punched cards.

Non-volatile memory technologies under development include ferroelectric RAM, programmable metallization cell, Spin-transfer torque magnetic RAM, SONOS, resistive random-access memory, racetrack memory, Nano-RAM, 3D XPoint, and millipede memory.

Semi-volatile memory
A third category of memory is semi-volatile. The term is used to describe a memory that has some limited non-volatile duration after power is removed, but then data is ultimately lost. A typical goal when using a semi-volatile memory is to provide the high performance and durability associated with volatile memories while providing some benefits of non-volatile memory.

For example, some non-volatile memory types experience wear when written. A worn cell has increased volatility but otherwise continues to work. Data locations which are written frequently can thus be directed to use worn circuits. As long as the location is updated within some known retention time, the data stays valid. After a period of time without update, the value is copied to a less-worn circuit with longer retention. Writing first to the worn area allows a high write rate while avoiding wear on the not-worn circuits.

As a second example, an STT-RAM can be made non-volatile by building large cells, but doing so raises the cost per bit and power requirements and reduces the write speed. Using small cells improves cost, power, and speed, but leads to semi-volatile behavior. In some applications, the increased volatility can be managed to provide many benefits of a non-volatile memory, for example by removing power but forcing a wake-up before data is lost; or by caching read-only data and discarding the cached data if the power-off time exceeds the non-volatile threshold.

The term semi-volatile is also used to describe semi-volatile behavior constructed from other memory types, such as nvSRAM, which combines SRAM and a non-volatile memory on the same chip, where an external signal copies data from the volatile memory to the non-volatile memory, but if power is removed before the copy occurs, the data is lost. Another example is battery-backed RAM, which uses an external battery to power the memory device in case of external power loss. If power is off for an extended period of time, the battery may run out, resulting in data loss.

Management
Proper management of memory is vital for a computer system to operate properly. Modern operating systems have complex systems to properly manage memory. Failure to do so can lead to bugs or slow performance.

Bugs
Improper management of memory is a common cause of bugs and security vulnerabilities, including the following types:

 * A memory leak occurs when a program requests memory from the operating system and never returns the memory when it is done with it. A program with this bug will gradually require more and more memory until the program fails as the operating system runs out.
 * A segmentation fault results when a program tries to access memory that it does not have permission to access. Generally, a program doing so will be terminated by the operating system.
 * A buffer overflow occurs when a program writes data to the end of its allocated space and then continues to write data beyond this to memory that has been allocated for other purposes. This may result in erratic program behavior, including memory access errors, incorrect results, a crash, or a breach of system security. They are thus the basis of many software vulnerabilities and can be maliciously exploited.

Virtual memory
Virtual memory is a system where physical memory is managed by the operating system typically with assistance from a memory management unit, which is part of many modern CPUs. It allows multiple types of memory to be used. For example, some data can be stored in RAM while other data is stored on a hard drive (e.g. in a swapfile), functioning as an extension of the cache hierarchy. This offers several advantages. Computer programmers no longer need to worry about where their data is physically stored or whether the user's computer will have enough memory. The operating system will place actively used data in RAM, which is much faster than hard disks. When the amount of RAM is not sufficient to run all the current programs, it can result in a situation where the computer spends more time moving data from RAM to disk and back than it does accomplishing tasks; this is known as thrashing.

Protected memory
Protected memory is a system where each program is given an area of memory to use and is prevented from going outside that range. If the operating system detects that a program has tried to alter memory that does not belong to it, the program is terminated (or otherwise restricted or redirected). This way, only the offending program crashes, and other programs are not affected by the misbehavior (whether accidental or intentional). Use of protected memory greatly enhances both the reliability and security of a computer system.

Without protected memory, it is possible that a bug in one program will alter the memory used by another program. This will cause that other program to run off of corrupted memory with unpredictable results. If the operating system's memory is corrupted, the entire computer system may crash and need to be rebooted. At times programs intentionally alter the memory used by other programs. This is done by viruses and malware to take over computers. It may also be used benignly by desirable programs which are intended to modify other programs, debuggers, for example, to insert breakpoints or hooks.

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

title: Computer memory


text:
Talk:Computer architecture

Comment 1
I'm worried about this page and a few others (one that I revised already) that 216.237.32.xxx has entered in today. They are suspiciously too good and comprehensive. I'm sure they are copied from somewhere, but I couldn't find them with a search engine. -- ansible
 * I'm -very- flattered. However, it's just me.  Ray Van De Walker,

and I have assented to GPL my writing in the Wikipedia. If you really like it, add it to the "good writing" link! (Something which I think would be unethical for me to do as author.)

Short description now *too* short?
You changed the short description from "Set of rules and methods that describe the functionality, organization, and implementation of computer systems" to just "Set of rules and methods".

Computer architectures are not the only sets of rules and methods in existence; is that short description too short, so as not to say anything about what computer architectures, in particular, are? Guy Harris (talk) 20:46, 7 July 2021 (UTC)
 * With short descriptions, we have a situation where we are aiming to have a maximum of 40 characters. The driving reason is that the short description is displayed on the mobile access to the article in a search result. 65% of access to Wikipedia is now via mobile devices or tablets. So we have that objective to display a short description that is readable on the mobile device. Descriptions over 40 characters get chopped off. With your forbearance, I ask, "What would you suggest?" --Whiteguru (talk) 22:19, 7 July 2021 (UTC)
 * "Set of rules describing computer system". 39 characters. Guy Harris (talk) 22:36, 7 July 2021 (UTC)
 * Well scribed! --Whiteguru (talk) 01:50, 8 July 2021 (UTC)

title: Talk:Computer architecture


text:
CDC (disambiguation)

The Centers for Disease Control and Prevention is the national public health agency of the United States.

CDC may also refer to:

Associations

 * Coalition to Diversify Computing, a joint organization of the Association for Computing Machinery (ACM) and the Computing Research Association (CRA)

Business

 * Caisse des dépôts et consignations ("Deposits and Consignments Fund"), a financial institution owned by the French government
 * Cameroon Development Corporation, an agribusiness company located in Limbe, Cameroon
 * CDC Group, formerly the Commonwealth Development Corporation and Colonial Development Corporation, a British development organisation owned by the UK Government
 * Central Depository Company, a Pakistani central securities depository company
 * ComfortDelGro Australia, a major Australian operator of buses formerly named ComfortDelGro Cabcharge
 * Control Data Corporation, former supercomputer company
 * Construction Data Company, also known as CDC News and CDC Publishing, a commercial construction reporting service
 * Loong Air, by ICAO code

Government

 * Africa Centres for Disease Control
 * Canadian Dairy Commission
 * Chichester District Council, local authority in West Sussex, England
 * Chinese Center for Disease Control and Prevention
 * Civil Defence Corps, UK, 1949-1968
 * Colonial Defence Committee, a body advising on the military defence of the British Empire, 1885-1908
 * Community Development Council, Singapore
 * Community of Democratic Choice, of Eastern European countries
 * Hong Kong Curriculum Development Council, Hong Kong
 * Korea Centers for Disease Control and Prevention, a South Korean agency
 * Taiwan Centers for Disease Control

Non-profit

 * Certified Development Company, a U.S. Small Business Administration program designed to provide financing for the purchase of fixed assets
 * Community development corporation, any non-profit organization that promotes and supports a community
 * Commission for Developing Countries, a Commission of the International Mathematical Union

Politics

 * California Democratic Council, US
 * Coalition for Democratic Change, a Liberian political alliance
 * Congress for Democratic Change, a Liberian political party
 * Democratic Convergence of Catalonia (Convergència Democràtica de Catalunya), a political party in Catalonia, Spain 1974–2016

Sport

 * Cricket Discipline Commission (of the England and Wales Cricket Board)

Other organizations

 * Cult of the Dead Cow (cDc), a computer hacker and DIY media organization

Places

 * Cedar City Regional Airport, by IATA code
 * Center Day Camp, North Windham, Maine, U.S.
 * Centre de documentation collégiale, library in  Quebec, Canada
 * Communicable Disease Centre, former hospital in Novena, Singapore

Science

 * Cell-division cycle in biology
 * cdc20
 * cdc25
 * Cdc42, cell-division cycle protein
 * Cholesterol-dependent cytolysin, exotoxins secreted by bacteria
 * Complement-dependent cytotoxicity
 * Conventional dendritic cell, cDC
 * Cross dehydrogenative coupling

Technology

 * Carbide-derived carbon
 * Change data capture, to track changed data
 * Clock domain crossing of a signal
 * Communications daughter card for notebook computers
 * Connected Device Configuration, of required Java ME features
 * USB communications device class

Other uses

 * CDC?, a children's book by William Steig
 * Chef de cuisine
 * Combat Direction Center of an aircraft carrier
 * Continuous Discharge Certificate, seafarer's identity document
 * Cul de canard, duck feathers used in fly fishing

title: CDC (disambiguation)


text:
Centers for Disease Control and Prevention

The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency under the Department of Health and Human Services, and is headquartered in Atlanta, Georgia.

The agency's main goal is the protection of public health and safety through the control and prevention of disease, injury, and disability in the US and worldwide. The CDC focuses national attention on developing and applying disease control and prevention. It especially focuses its attention on infectious disease, food borne pathogens, environmental health, occupational safety and health, health promotion, injury prevention, and educational activities designed to improve the health of United States citizens. The CDC also conducts research and provides information on non-infectious diseases, such as obesity and diabetes, and is a founding member of the International Association of National Public Health Institutes.

The CDC's current Director is Mandy Cohen who assumed office on July 10, 2023.

Establishment
The Communicable Disease Center was founded July 1, 1946, as the successor to the World War II Malaria Control in War Areas program of the Office of National Defense Malaria Control Activities.

Preceding its founding, organizations with global influence in malaria control were the Malaria Commission of the League of Nations and the Rockefeller Foundation. The Rockefeller Foundation greatly supported malaria control, sought to have the governments take over some of its efforts, and collaborated with the agency.

The new agency was a branch of the U.S. Public Health Service and Atlanta was chosen as the location because malaria was endemic in the Southern United States. The agency changed names (see infobox on top) before adopting the name Communicable Disease Center in 1946. Offices were located on the sixth floor of the Volunteer Building on Peachtree Street.

With a budget at the time of about $1million, 59 percent of its personnel were engaged in mosquito abatement and habitat control with the objective of control and eradication of malaria in the United States (see National Malaria Eradication Program).

Among its 369 employees, the main jobs at CDC were originally entomology and engineering. In CDC's initial years, more than six and a half million homes were sprayed, mostly with DDT. In 1946, there were only seven medical officers on duty and an early organization chart was drawn. Under Joseph Walter Mountin, the CDC continued to be an advocate for public health issues and pushed to extend its responsibilities to many other communicable diseases.

In 1947, the CDC made a token payment of $10 to Emory University for 15 acre of land on Clifton Road in DeKalb County, still the home of CDC headquarters as of 2019. CDC employees collected the money to make the purchase. The benefactor behind the "gift" was Robert W. Woodruff, chairman of the board of The Coca-Cola Company. Woodruff had a long-time interest in malaria control, which had been a problem in areas where he went hunting. The same year, the PHS transferred its San Francisco based plague laboratory into the CDC as the Epidemiology Division, and a new Veterinary Diseases Division was established.

Growth
In 1951, Chief Epidemiologist Alexander Langmuir's warnings of potential biological warfare during the Korean War spurred the creation of the Epidemic Intelligence Service (EIS) as a two-year postgraduate training program in epidemiology. The success of the EIS program led to the launch of Field Epidemiology Training Programs (FETP) in 1980, training more than 18,000 disease detectives in over 80 countries. In 2020, FETP celebrated the 40th anniversary of the CDC's support for Thailand's Field Epidemiology Training Program. Thailand was the first FETP site created outside of North America and is found in numerous countries, reflecting CDC's influence in promoting this model internationally. The Training Programs in Epidemiology and Public Health Interventions Network (TEPHINET) has graduated 950 students.

The mission of the CDC expanded beyond its original focus on malaria to include sexually transmitted diseases when the Venereal Disease Division of the U.S. Public Health Service (PHS) was transferred to the CDC in 1957. Shortly thereafter, Tuberculosis Control was transferred (in 1960) to the CDC from PHS, and then in 1963 the Immunization program was established.

It became the National Communicable Disease Center effective July 1, 1967, and the Center for Disease Control on June 24, 1970. At the end of the Public Health Service reorganizations of 1966–1973, it was promoted to being a principal operating agency of PHS.

Recent history
It was renamed to the plural Centers for Disease Control effective October 14, 1980, as the modern organization of having multiple constituent centers was established. By 1990, it had four centers formed in the 1980s: the Center for Infectious Diseases, Center for Chronic Disease Prevention and Health Promotion, the Center for Environmental Health and Injury Control, and the Center for Prevention Services; as well as two centers that had been absorbed by CDC from outside: the National Institute for Occupational Safety and Health in 1973, and the National Center for Health Statistics in 1987.

An act of the United States Congress appended the words "and Prevention" to the name effective October 27, 1992. However, Congress directed that the initialism CDC be retained because of its name recognition. Since the 1990s, the CDC focus has broadened to include chronic diseases, disabilities, injury control, workplace hazards, environmental health threats, and terrorism preparedness. CDC combats emerging diseases and other health risks, including birth defects, West Nile virus, obesity, avian, swine, and pandemic flu, E. coli, and bioterrorism, to name a few. The organization would also prove to be an important factor in preventing the abuse of penicillin. In May 1994 the CDC admitted having sent samples of communicable diseases to the Iraqi government from 1984 through 1989 which were subsequently repurposed for biological warfare, including Botulinum toxin, West Nile virus, Yersinia pestis and Dengue fever virus.

On April 21, 2005, then–CDC Director Julie Gerberding formally announced the reorganization of CDC to "confront the challenges of 21st-century health threats". She established four Coordinating Centers. In 2009 the Obama Administration re-evaluated this change and ordered them cut as an unnecessary management layer.

As of 2013, the CDC's Biosafety Level 4 laboratories were among the few that exist in the world. They included one of only two official repositories of smallpox in the world, with the other one located at the State Research Center of Virology and Biotechnology VECTOR in the Russian Federation. In 2014, the CDC revealed they had discovered several misplaced smallpox samples while their lab workers were "potentially infected" with anthrax.

The city of Atlanta annexed the property of the CDC headquarters effective January 1, 2018, as a part of the city's largest annexation within a period of 65 years; the Atlanta City Council had voted to do so the prior December. The CDC and Emory University had requested that the Atlanta city government annex the area, paving the way for a MARTA expansion through the Emory campus, funded by city tax dollars. The headquarters were located in an unincorporated area, statistically in the Druid Hills census-designated place.

On August 17, 2022, Dr. Walensky said the CDC would make drastic changes in the wake of mistakes during the COVID-19 pandemic. She outlined an overhaul of how the CDC would analyze and share data and how they would communicate information to the general public. In her statement to all CDC employees, she said: "For 75 years, CDC and public health have been preparing for COVID-19, and in our big moment, our performance did not reliably meet expectations." Based on the findings of an internal report, Walensky concluded that "The CDC must refocus itself on public health needs, respond much faster to emergencies and outbreaks of disease, and provide information in a way that ordinary people and state and local health authorities can understand and put to use" (as summarized by the New York Times).

Organization
The CDC is organized into "Centers, Institutes, and Offices" (CIOs), with each organizational unit implementing the agency's activities in a particular area of expertise while also providing intra-agency support and resource-sharing for cross-cutting issues and specific health threats.

As of the most recent reorganization in February 2023, the CIOs are:
 * Director
 * National Center for Immunization and Respiratory Diseases
 * National Center for Emerging and Zoonotic Infectious Diseases
 * Division of Global Migration Health
 * National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention
 * National Center on Birth Defects and Developmental Disabilities
 * National Center for Chronic Disease Prevention and Health Promotion
 * National Center for Environmental Health / Agency for Toxic Substances and Disease Registry
 * National Center for Injury Prevention and Control
 * National Institute for Occupational Safety and Health
 * Public Health Infrastructure Center
 * Global Health Center
 * Immediate Office of the Director
 * Chief of Staff
 * Office of the Chief Operating Officer
 * Office of Policy, Performance, and Evaluation
 * Office of Equal Employment Opportunity and Workplace Equity
 * Office of Communications
 * Office of Health Equity
 * Office of Science
 * CDC Washington Office
 * Office of Laboratory Science and Safety
 * Office of Readiness and Response
 * Center for Forecasting and Outbreak Analytics
 * Office of Public Health Data, Surveillance, and Technology
 * National Center for Health Statistics

The Office of Public Health Preparedness was created during the 2001 anthrax attacks shortly after the terrorist attacks of September 11, 2001. Its purpose was to coordinate among the government the response to a range of biological terrorism threats.

Locations
Most CDC centers are located in Atlanta. Building 18, which opened in 2005 at the CDC's main Roybal campus (named in honor of the late Representative Edward R. Roybal), contains the premier BSL4 laboratory in the United States.

A few of the centers are based in or operate other domestic locations:
 * The National Center for Health Statistics is primarily located in Hyattsville, Maryland, with a branch in Research Triangle Park in North Carolina.
 * The National Institute for Occupational Safety and Health's primary locations are Cincinnati; Morgantown, West Virginia; Pittsburgh; Spokane, Washington; and Washington, D.C., with branches in Denver; Anchorage, Alaska; and Atlanta.
 * The CDC Washington Office is based in Washington, D.C.
 * Two divisions of the National Center for Emerging and Zoonotic Infectious Diseases are based outside Atlanta. The Division of Vector-Borne Diseases is based in Fort Collins, Colorado, with a branch in San Juan, Puerto Rico.  The Arctic Investigations Program is based in Anchorage.

In addition, CDC operates quarantine facilities in 20 cities in the U.S.

Budget
CDC's budget for fiscal year 2018 was $11.9billion; this decreased to $11.09 billion for fiscal year 2019. The CDC offers grants to help organizations advance health, safety and awareness at the community level in the United States. The CDC awards over 85 percent of its annual budget through these grants.

Workforce
CDC staff numbered approximately 15,000 personnel (including 6,000 contractors and 840 United States Public Health Service Commissioned Corps officers) in 170 occupations. Eighty percent held bachelor's degrees or higher; almost half had advanced degrees (a master's degree or a doctorate such as a PhD, D.O., or M.D.).

Common CDC job titles include engineer, entomologist, epidemiologist, biologist, physician, veterinarian, behavioral scientist, nurse, medical technologist, economist, public health advisor, health communicator, toxicologist, chemist, computer scientist, and statistician. The CDC also operates a number of notable training and fellowship programs, including those indicated below.

Epidemic Intelligence Service (EIS)
The Epidemic Intelligence Service (EIS) is composed of "boots-on-the-ground disease detectives" who investigate public health problems domestically and globally. When called upon by a governmental body, EIS officers may embark on short-term epidemiological assistance assignments, or "Epi-Aids", to provide technical expertise in containing and investigating disease outbreaks. The EIS program is a model for the international Field Epidemiology Training Program.

Public Health Associates Program
The CDC also operates the Public Health Associate Program (PHAP), a two-year paid fellowship for recent college graduates to work in public health agencies all over the United States. PHAP was founded in 2007 and currently has 159 associates in 34 states.

Leadership

The Director of CDC is a Senior Executive Service position that may be filled either by a career employee, or as a political appointment that does not require Senate confirmation, with the latter method typically being used. The director serves at the pleasure of the President and may be fired at any time. On January 20, 2025, the CDC Director position will change to require Senate confirmation, due to a provision in the Consolidated Appropriations Act, 2023. The CDC Director concurrently serves as the Administrator of the Agency for Toxic Substances and Disease Registry.

Twenty directors have served the CDC or its predecessor agencies, including three who have served during the Trump administration (including Anne Schuchat who twice served as acting director) and three who have served during the Carter administration (including one acting director not shown here). Two served under Bill Clinton, but only one under the Nixon to Ford terms.

Datasets and survey systems

 * CDC Scientific Data, Surveillance, Health Statistics, and Laboratory Information.
 * Behavioral Risk Factor Surveillance System (BRFSS), the world's largest, ongoing telephone health-survey system.
 * Pregnancy Risk Assessment Monitoring System (PRAMS), a surveillance system on maternal and infant health with telephone and mail questionnaires in English and Spanish in 50 US jurisdictions.
 * Mortality Medical Data System.
 * Abortion statistics in the United States
 * CDC WONDER (Wide-ranging ONline Data for Epidemiologic Research)
 * Data systems of the National Center for Health Statistics

Communicable diseases
The CDC's programs address more than 400 diseases, health threats, and conditions that are major causes of death, disease, and disability. The CDC's website has information on various infectious (and noninfectious) diseases, including smallpox, measles, and others.

Influenza
The CDC targets the transmission of influenza, including the H1N1 swine flu, and launched websites to educate people about hygiene.

Division of Select Agents and Toxins
Within the division are two programs: the Federal Select Agent Program (FSAP) and the Import Permit Program. The FSAP is run jointly with an office within the U.S. Department of Agriculture, regulating agents that can cause disease in humans, animals, and plants. The Import Permit Program regulates the importation of "infectious biological materials."

The CDC runs a program that protects the public from rare and dangerous substances such as anthrax and the Ebola virus. The program, called the Federal Select Agent Program, calls for inspections of labs in the U.S. that work with dangerous pathogens.

During the 2014 Ebola outbreak in West Africa, the CDC helped coordinate the return of two infected American aid workers for treatment at Emory University Hospital, the home of a special unit to handle highly infectious diseases.

As a response to the 2014 Ebola outbreak, Congress passed a Continuing Appropriations Resolution allocating $30,000,000 towards CDC's efforts to fight the virus.

Non-communicable diseases
The CDC also works on non-communicable diseases, including chronic diseases caused by obesity, physical inactivity and tobacco-use. The work of the Division for Cancer Prevention and Control, led from 2010 by Lisa C. Richardson, is also within this remit.

Antibiotic resistance
The CDC implemented their National Action Plan for Combating Antibiotic Resistant Bacteria as a measure against the spread of antibiotic resistance in the United States. This initiative has a budget of $161million and includes the development of the Antibiotic Resistance Lab Network.

Global health
Globally, the CDC works with other organizations to address global health challenges and contain disease threats at their source. They work with many international organizations such as the World Health Organization (WHO) as well as ministries of health and other groups on the front lines of outbreaks. The agency maintains staff in more than 60 countries, including some from the U.S. but more from the countries in which they operate. The agency's global divisions include the Division of Global HIV and TB (DGHT), the Division of Parasitic Diseases and Malaria (DPDM), the Division of Global Health Protection (DGHP), and the Global Immunization Division (GID).

The CDC has been working with the WHO to implement the International Health Regulations (IHR), an agreement between 196 countries to prevent, control, and report on the international spread of disease, through initiatives including the Global Disease Detection Program (GDD).

The CDC has also been involved in implementing the U.S. global health initiatives President's Emergency Plan for AIDS Relief (PEPFAR) and President's Malaria Initiative.

Travelers' health
The CDC collects and publishes health information for travelers in a comprehensive book, CDC Health Information for International Travel, which is commonly known as the "yellow book." The book is available online and in print as a new edition every other year and includes current travel health guidelines, vaccine recommendations, and information on specific travel destinations. The CDC also issues travel health notices on its website, consisting of three levels:
 * "Watch": Level 1 (practice usual precautions)
 * "Alert": Level 2 (practice enhanced precautions)
 * "Warning": Level 3 (avoid nonessential travel)

Vaccine safety
The CDC uses a number of tools to monitor the safety of vaccines. The Vaccine Adverse Event Reporting System (VAERS), a national vaccine safety surveillance program run by CDC and the FDA. "VAERS detects possible safety issues with U.S. vaccines by collecting information about adverse events (possible side effects or health problems) after vaccination." The CDC's Safety Information by Vaccine page provides a list of the latest safety information, side effects, and answers to common questions about CDC recommended vaccines.

The Vaccine Safety Datalink (VSD) works with a network of healthcare organizations to share data on vaccine safety and adverse events. The Clinical Immunization Safety Assessment (CISA) project is a network of vaccine experts and health centers that research and assist the CDC in the area of vaccine safety.

CDC also runs a program called V-safe, a smartphone web application that allows COVID-19 vaccine recipients to be surveyed in detail about their health in response to getting the shot.

CDC Foundation
The CDC Foundation operates independently from CDC as a private, nonprofit 501(c)(3) organization incorporated in the State of Georgia. The creation of the Foundation was authorized by section 399F of the Public Health Service Act to support the mission of CDC in partnership with the private sector, including organizations, foundations, businesses, educational groups, and individuals. From 1995 to 2022, the Foundation raised over $1.6 billion and launched more than 1,200 health programs. Bill Cosby formerly served as a member of the Foundation's Board of Directors, continuing as an honorary member after completing his term.

Activities
The Foundation engages in research projects and health programs in more than 160 countries every year, including in focus areas such as cardiovascular disease, cancer, emergency response, and infectious diseases, particularly HIV/AIDS, Ebola, rotavirus, and COVID-19.
 * EmPOWERED Health Program: Launched in November 2019 with funding from Amgen, the program works to empower cancer patients to become actively involved in the decision making around their treatments.
 * Fries Prize for Improving Health: An annual prize first awarded in 1992 that "recognizes an individual who has made major accomplishments in health improvement and with the general criteria of the greatest good for the greatest number".

Criticism
In 2015, BMJ associate editor Jeanne Lenzer raised concerns that the CDC's recommendations and publications may be influenced by donations received through the Foundation, which includes pharmaceutical companies.

Tuskegee study of untreated syphilis in Black men
For 15 years, the CDC had direct oversight over the Tuskegee syphilis experiment. In the study, which lasted from 1932 to 1972, a group of Black men (nearly 400 of whom had syphilis) were studied to learn more about the disease. The disease was left untreated in the men, who had not given their informed consent to serve as research subjects. The Tuskegee Study was initiated in 1932 by the Public Health Service, with the CDC taking over the Tuskegee Health Benefit Program in 1995.

Gun control
An area of partisan dispute related to CDC funding is studying firearms effectiveness. Although the CDC was one of the first government agencies to study gun related data, in 1996 the Dickey Amendment, passed with the support of the National Rifle Association of America, states "none of the funds available for injury prevention and control at the Centers for Disease Control and Prevention may be used to advocate or promote gun control". Advocates for gun control oppose the amendment and have tried to overturn it.

Looking at the history of the passage of the Dickey Amendment, in 1992, Mark L. Rosenberg and five CDC colleagues founded the CDC's National Center for Injury Prevention and Control, with an annual budget of approximately $260,000. They focused on "identifying causes of firearm deaths, and methods to prevent them". Their first report, published in the New England Journal of Medicine in 1993 entitled "Guns are a Risk Factor for Homicide in the Home", reported "mere presence of a gun in a home increased the risk of a firearm-related death by 2.7 percent, and suicide fivefold—a "huge" increase." In response, the NRA launched a "campaign to shut down the Injury Center." Two conservative pro-gun groups, Doctors for Responsible Gun Ownership and Doctors for Integrity and Policy Research joined the pro-gun effort, and, by 1995, politicians also supported the pro-gun initiative. In 1996, Jay Dickey (R) Arkansas introduced the Dickey Amendment statement stating "none of the funds available for injury prevention and control at the Centers for Disease Control and Prevention may be used to advocate or promote gun control" as a rider. in the 1996 appropriations bill." In 1997, "Congress re-directed all of the money for gun research to the study of traumatic brain injury." David Satcher, CDC head 1993-98 advocated for firearms research. In 2016 over a dozen "public health insiders, including current and former CDC senior leaders" told The Trace interviewers that CDC senior leaders took a cautious stance in their interpretation of the Dickey Amendment and that they could do more but were afraid of political and personal retribution.

In 2013, the American Medical Association, the American Psychological Association, and the American Academy of Pediatrics sent a letter to the leaders of the Senate Appropriations Committee asking them "to support at least $10million within the Centers for Disease Control and Prevention (CDC) in FY 2014 along with sufficient new taxes at the National Institutes of Health to support research into the causes and prevention of violence. Furthermore, we urge Members to oppose any efforts to reduce, eliminate, or condition CDC funding related to violence prevention research." Congress maintained the ban in subsequent budgets.

Ebola
In October 2014, the CDC gave a nurse with a fever who was later diagnosed with Ebola permission to board a commercial flight to Cleveland.

COVID-19
The CDC has been widely criticized for its handling of the COVID-19 pandemic. In 2022, CDC director Rochelle Walensky acknowledged "some pretty dramatic, pretty public mistakes, from testing to data to communications", based on the findings of an internal examination.

The first confirmed case of COVID-19 was discovered in the U.S. on January 20, 2020. However, widespread COVID-19 testing in the United States was effectively stalled until February 28, when federal officials revised a faulty CDC test, and days afterward, when the Food and Drug Administration began loosening rules that had restricted other labs from developing tests. In February 2020, as the CDC's early coronavirus test malfunctioned nationwide, CDC Director Robert R. Redfield reassured fellow officials on the White House Coronavirus Task Force that the problem would be quickly solved, according to White House officials. It took about three weeks to sort out the failed test kits, which may have been contaminated during their processing in a CDC lab. Later investigations by the FDA and the Department of Health and Human Services found that the CDC had violated its own protocols in developing its tests. In November 2020, NPR reported that an internal review document they obtained revealed that the CDC was aware that the first batch of tests which were issued in early January had a chance of being wrong 33 percent of the time, but they released them anyway.

In May 2020, The Atlantic reported that the CDC was conflating the results of two different types of coronavirus tests — tests that diagnose current coronavirus infections, and tests that measure whether someone has ever had the virus. The magazine said this distorted several important metrics, provided the country with an inaccurate picture of the state of the pandemic, and overstated the country's testing ability.

In July 2020, the Trump administration ordered hospitals to bypass the CDC and instead send all COVID-19 patient information to a database at the Department of Health and Human Services. Some health experts opposed the order and warned that the data might become politicized or withheld from the public. On July 15, the CDC alarmed health care groups by temporarily removing COVID-19 dashboards from its website. It restored the data a day later.

In August 2020, the CDC recommended that people showing no COVID-19 symptoms do not need testing. The new guidelines alarmed many public health experts. The guidelines were crafted by the White House Coronavirus Task Force without the sign-off of Anthony Fauci of the NIH. Objections by other experts at the CDC went unheard. Officials said that a CDC document in July arguing for "the importance of reopening schools" was also crafted outside the CDC. On August 16, the chief of staff, Kyle McGowan, and his deputy, Amanda Campbell, resigned from the agency. The testing guidelines were reversed on September 18, 2020, after public controversy.

In September 2020, the CDC drafted an order requiring masks on all public transportation in the United States, but the White House Coronavirus Task Force blocked the order, refusing to discuss it, according to two federal health officials.

In October 2020, it was disclosed that White House advisers had repeatedly altered the writings of CDC scientists about COVID-19, including recommendations on church choirs, social distancing in bars and restaurants, and summaries of public-health reports.

In the lead up to 2020 Thanksgiving, the CDC advised Americans not to travel for the holiday saying, "It's not a requirement. It's a recommendation for the American public to consider." The White House coronavirus task force had its first public briefing in months on that date but travel was not mentioned.

The New York Times later concluded that the CDC's decisions to "ben[d] to political pressure from the Trump White House to alter key public health guidance or withhold it from the public [...] cost it a measure of public trust that experts say it still has not recaptured" as of 2022.

In May 2021, following criticism by scientists, the CDC updated its COVID-19 guidance to acknowledge airborne transmission of COVID-19, after having previously claimed that the majority of infections occurred via "close contact, not airborne transmission".

In December 2021, following a request from the CEO of Delta Air Lines, CDC shortened its recommended isolation period for asymptomatic individuals infected with Covid-19 from 10 days to five.

Until 2022, the CDC withheld critical data about COVID-19 vaccine boosters, hospitalizations and wastewater data.

On June 10, 2022, the Biden Administration ordered the CDC to remove the COVID-19 testing requirement for air travelers entering the United States.

In January 2022, it was revealed that the CDC had communicated with moderators at Facebook and Instagram over COVID-19 information and discussion on the platforms, including information that the CDC considered false or misleading and that might influence people not to get the COVID-19 vaccines.

Controversy over the Morbidity and Mortality Weekly Report
During the pandemic, the CDC Morbidity and Mortality Weekly Report (MMWR) came under pressure from political appointees at the Department of Health and Human Services (HHS) to modify its reporting so as not to conflict with what Trump was saying about the pandemic.

Starting in June 2020, Michael Caputo, the HHS assistant secretary for public affairs, and his chief advisor Paul Alexander tried to delay, suppress, change, and retroactively edit MMR releases about the effectiveness of potential treatments for COVID-19, the transmissibility of the virus, and other issues where the president had taken a public stance. Alexander tried unsuccessfully to get personal approval of all issues of MMWR before they went out.

Caputo claimed this oversight was necessary because MMWR reports were being tainted by "political content"; he demanded to know the political leanings of the scientists who reported that hydroxychloroquine had little benefit as a treatment while Trump was saying the opposite. In emails Alexander accused CDC scientists of attempting to "hurt the president" and writing "hit pieces on the administration".

In October 2020, emails obtained by Politico showed that Alexander requested multiple alterations in a report. The published alterations included a title being changed from "Children, Adolescents, and Young Adults" to "Persons." One current and two former CDC officials who reviewed the email exchanges said they were troubled by the "intervention to alter scientific reports viewed as untouchable prior to the Trump administration" that "appeared to minimize the risks of the coronavirus to children by making the report's focus on children less clear."

Eroding trust in the CDC as a result of COVID-19 controversies
A poll conducted in September 2020 found that nearly 8 in 10 Americans trusted the CDC, a decrease from 87 percent in April 2020. Another poll showed an even larger drop in trust with the results dropping 16 percentage points. By January 2022, according to an NBC News poll, only 44% of Americans trusted the CDC compared to 69% at the beginning of the pandemic. As the trustworthiness eroded, so too did the information it disseminates. The diminishing level of trust in the CDC and the information releases also incited "vaccine hesitancy" with the result that "just 53 percent of Americans said they would be somewhat or extremely likely to get a vaccine."

In September 2020, amid the accusations and the faltering image of the CDC, the agency's leadership was called into question. Former acting director at the CDC, Richard Besser, said of Redfield that "I find it concerning that the CDC director has not been outspoken when there have been instances of clear political interference in the interpretation of science." In addition, Mark Rosenberg, the first director of CDC's National Center for Injury Prevention and Control, also questioned Redfield's leadership and his lack of defense of the science.

Historically, the CDC has not been a political agency; however, the COVID-19 pandemic, and specifically the Trump Administration's handling of the pandemic, resulted in a "dangerous shift" according to a previous CDC director and others. Four previous directors claim that the agency's voice was "muted for political reasons." Politicization of the agency has continued into the Biden administration as COVID-19 guidance is contradicted by State guidance and the agency is criticized as "CDC's credibility is eroding".

In 2021, the CDC, then under the leadership of the Biden Administration, received criticism for its mixed messaging surrounding COVID-19 vaccines, mask-wearing guidance, and the state of the pandemic.

Sex assignment
In 2024, evolutionary biologist Richard Dawkins and physicist Alan Sokal co-authored an op-ed in The Boston Globe criticizing the use of the terminology "sex assigned at birth" instead of "sex" by the CDC, the American Medical Association, the American Psychological Association, and the American Academy of Pediatrics. Dawkins and Sokal argued that sex is an "objective biological reality" that "is determined at conception and is then observed at birth," rather than assigned by a medical professional. Calling this "social constructionism gone amok", Dawkins and Sokal argued further that "distort[ing] the scientific facts in the service of a social cause" risks undermining trust in medical institutions.

Publications

 * CDC publications
 * State of CDC report
 * CDC Programs in Brief
 * Morbidity and Mortality Weekly Report
 * Emerging Infectious Diseases (monthly journal)
 * Preventing Chronic Disease
 * Vital statistics

Zombie Apocalypse campaign
On May 16, 2011, the Centers for Disease Control and Prevention's blog published an article instructing the public on what to do to prepare for a zombie invasion. While the article did not claim that such a scenario was possible, it did use the popular culture appeal as a means of urging citizens to prepare for all potential hazards, such as earthquakes, tornadoes, and floods.

According to David Daigle, the associate director for Communications, Public Health Preparedness and Response, the idea arose when his team was discussing their upcoming hurricane-information campaign and Daigle mused that "we say pretty much the same things every year, in the same way, and I just wonder how many people are paying attention." A social-media employee mentioned that the subject of zombies had come up a lot on Twitter when she had been tweeting about the Fukushima Daiichi nuclear disaster and radiation. The team realized that a campaign like this would most likely reach a different audience from the one that normally pays attention to hurricane-preparedness warnings and went to work on the zombie campaign, launching it right before hurricane season began. "The whole idea was, if you're prepared for a zombie apocalypse, you're prepared for pretty much anything," said Daigle.

Once the blog article was posted, the CDC announced an open contest for YouTube submissions of the most creative and effective videos covering preparedness for a zombie apocalypse (or apocalypse of any kind), to be judged by the "CDC Zombie Task Force". Submissions were open until October 11, 2011. They also released a zombie-themed graphic novella available on their website. Zombie-themed educational materials for teachers are available on the site.

CDC Departments

 * ATSDR - CDC department
 * NIOSH - CDC department
 * N95 respirator - regulated by NIOSH
 * Division of Industrial Hygiene - predecessor to NIOSH

Other US Executive Departments

 * MSHA - co-regulator of respirators prior to 1998
 * Bureau of Mines - predecessor to MSHA
 * National Highway Traffic Safety Administration
 * OSHA


text:
Talk:Centers for Disease Control and Prevention

New logo
Hi everyone,

I noticed recently that the CDC webpage has been revamped and the organization has released a new version of their logo. I reached out to their general information e-mail, and a representative confirmed that the new logo is “the updated logo for CDC in general”. Can anyone locate (or create) a .SVG logo equivalent so that the article’s infobox logo may be updated? Thanks! L337p4wnTalk to me! 19:09, 25 May 2024 (UTC)