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CompactFlash

From Academic Kids

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A 64 MB CompactFlash Type I card

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 a 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 eventially switched over to NAND. CF is among the oldest and most successfull formats, and has held on to a niche in the professional camera market especially well. It has benifited from having both a good cost to memory size ratio relative to other formats for much of its life, and generally having larger capacities avaible over 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 directtly 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).

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A 32 MB High Speed CompactFlash Type I card
Contents

Description

NOR-based flash has lower density than newer NAND-based systems, and Compact Flash 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 SSDFC (SmartMedia). 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 36mm 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 then the even earlier PC Card (PCMCIA) Type I memory cards, except for its thickness which matches PC Card Type I and Type II widths respectively. CF has managed to be the most successfull 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 then 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 then even CF had been in respect to PC Card. These new formats would dominate PDAs, cell phones, and consumer camera's (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 capacitity then 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 then some other types as well, since it is only a un-powered 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 12 mbit/s write and 24 mbit/s read). 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. (Here, one megabyte is defined as 1 million bytes, and one gigabyte is defined as 1000 million bytes.)

Microdrives

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IBM 1 GB Microdrive

see Microdrive for the main entry on this subject area

Microdrives are tiny hard disks (about 1 inch wide) that are for CompactFlash Type II. They were developed by and released in 1999 by IBM in a 340 megabyte capacity. The the division 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 6 GB as of mid 2005).

While these drives fit into any CF II slot, they take more power on average than flash memory 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.

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.

For this reason a new CF standard, CF+ (or CF 2.0), has been drawn up. It includes two major changes, an increase in speed to 16 MB/s data-transfer, and capacities up to 137 GB (according to the CompactFlash Association (CFA))

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

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:

See also

External links

he:CompactFlash it:CompactFlash ja:コンパクトフラッシュ ru:CompactFlash

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