CompactFlash

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CompactFlash (CF) was originally a type of data storage device, used in portable electronic devices. As a storage device, it typically uses flash memory in a standardized enclosure, and was first specified and produced by SanDisk Corporation in 1994. The physical format is now used for a variety of devices. There are two main subdivisions of CF cards, Type I and the slightly thicker Type II cards. There are two, soon to be three, main speeds of cards including the original CF, CF High Speed (using CF+/CF2.0), and an even faster CF3.0 standard that is being adopted as of 2005. The CF Type II slot is used by Microdrives and some other devices.

CF was among the first flash memory standards to compete with the earlier and larger PC Card Type I memory cards, and was originally built around Intel's NOR-based flash memory, though it switched over to NAND. CF is among the oldest and most successful formats, and has held on to a niche in the professional camera market especially well. It has benefited from having both a good cost to memory size ratio relative to other formats for much of its life, and generally having larger capacities available than smaller formats.

CF cards can be used directly in PC Card slot with a plug adapter, and with a reader, to any number of common ports like USB or FireWire. More impressively, thanks to its bigger size relative to the smaller cards that came later, many other formats can be used directly in a CF card slot with an adapter (including SD/MMC, Memory Stick Duo, xD-Picture Card in a Type I slot, and SmartMedia in a Type II slot, as of 2005) (some multi-card readers use CF for I/O as well).

1 Description
2 Microdrives
3 CF+ specification
4 Other devices conforming to the CF standard
5 See also
6 External links

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Description

Image:Loading a cf card into canon a95.jpg NOR-based flash has lower density than newer NAND-based systems, and CompactFlash is therefore the largest of the three memory card formats that came out in the early 1990s, the other two being Miniature Card (MiniCard) and SmartMedia(SSDFC). However, CF did switch to NAND type memory later on. Also, the IBM Microdrive format which used CF Type II was not solid state memory.

CompactFlash defines a physical interface which is smaller than, but electrically identical to, the PCMCIA-ATA interface. That is, it appears to the host device as if it were a hard disk of some defined size and has a tiny IDE controller onboard the CF device itself. The connector is about 43 mm wide, and the case is 36 mm deep and comes in two standard thicknesses, CF I (3.3 mm), and CF II (5 mm). Both types are otherwise identical. CF I cards can be used in CF II slots, but CF II cards are too thick to fit in CF I slots. Flash memory cards are usually CF I.

CF cards are much more compact than the even earlier PC Card (PCMCIA) Type I memory cards, except for its thickness which matches PC Card Type I and Type II thicknesses respectively. CF has managed to be the most successful of the early memory card formats, outliving both Miniature Card, SmartMedia, and PC Card Type I in mainstream popularity. SmartMedia did offer heavy competition to CF in smaller devices, and was more popular than CF at its peak in terms of market penetration, but SmartMedia would cede this area to newer card types (during the period of roughly 2002-2005).

The memory card formats that came out in the late 1990s to the early 2000s (SD/MMC, various Memory Stick formats, xD-Picture Card, etc.) offered stiff competition. The new smaller formats were a fraction of the size of CF, in some cases smaller than even CF had been in respect to PC Card. These new formats would dominate PDAs, cell phones, and consumer cameras (especially subcompact models).

However, CF continues to be offered on many devices, and remains the main standard for professional cameras, as well as a number of consumer models as of 2005. Key features remain having a decent cost per MB, offering a larger top capacity than smaller cards, the ability for the CF II to use MicroDrive, and adapters that allow a CF slot to use many other smaller card formats. Adapters for CF into PC Cards slots are also cheaper than some other types, since it is only an unpowered plug adapter with no chips inside.

Of note is that CF (and other formats) have not managed to totally replace PC Card Type I and II Memory cards in a number of industrial applications.

Flash memory devices are non-volatile and solid state, and thus are more robust than disk drives, and consume around 5% of the power required by small disk drives, and yet still have good transfer speeds (up to 20 Mbyte/s write and 20 Mbyte/s read for the SanDisk Extreme III). They operate at 3.3 volts or 5 volts, and can be swapped from system to system. CF cards with flash memory are able to cope with extremely rapid changes in temperature. Industrial versions of flash memory cards can operate at a range of -45 to +85 °C.

CF devices are used in handheld and laptop computers (which may or may not take larger form-factor cards), digital cameras, and a wide variety of other devices, including desktop computers.

As of 2005, CompactFlash cards are available in capacities from about 8 megabytes to about 12 gigabytes, perhaps the most popular choices being between 128 MB and 1 GB (in Europe and America). Lower capacity cards are becoming rare in stores.

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Microdrives

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Microdrives are tiny hard disks (about 1 inch / 25 mm wide) packaged with a CompactFlash Type II form factor and interface. They were developed and released in 1999 by IBM in a 170 megabyte capacity. Then the division was sold to Hitachi in December 2002 along with the Microdrive trademark. There are now other brands that sell Microdrives (such as Seagate, Sony, etc), and, over the years, these have become available in increasingly larger capacities (up to 8 GB as of Oct. 2005).

While these drives fit into any CF II slot, they take more power on average (500mA maximum) than flash memory (100mA maximum) and so may not work in some low-power devices (for example, NEC HPCs). Being a mechanical device they are more sensitive to physical shock and temperature changes than flash memory, though in practice they are very robust.

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CF+ specification

When CompactFlash was first being standardized, even full-sized hard disks were rarely larger than 4 GB in size, and so the existing limitations of the ATA standard were considered acceptable. Since then hard disks have had to make many modifications to the ATA system to handle ever-growing media, and today even flash memory cards have been able to pass the 4 GB limit. However, CF cards since the original Revision 1.0 have been able to support capacities up to 137GB.

The CF+ standard, Revision 2.0), added an increase in speed to 16 Mbyte/s data-transfer,(according to the CompactFlash Association (CFA))

The CF 3.0 standard has also been released which supports up to 66 Mbyte/s data transfer rates, and a number of other features.

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Other devices conforming to the CF standard

The CompactFlash format is also used for a variety of Input/Output and interface devices. Since it is electrically identical to the PC Card, many PC cards have CF counterparts. Some examples include: