Science Fair Project Encyclopedia
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.
NOR-based flash has lower density than newer NAND-based systems, and Compact Flash is therefore (in spite of its name) larger than later standards like MMC, SD, or Memory Stick. CF memory cards are usually cheaper than cards of the same capacity conforming to those other standards.
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. 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.
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. 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°C to +85°C.
As of 2004, CompactFlash cards are available in capacities from about 8 megabytes to about 8 gigabytes. (Here, one megabyte is defined as 1 million bytes, and one gigabyte is defined as 1000 million bytes.)
Originally released in 1999 by IBM in a 340 megabyte capacity, and now made by Hitachi, Microdrives are tiny hard disks that fit into the CF II format. Over the years, these have become available in increasingly larger capacities:
|2001||– 1 gigabyte (IBM)|
|2003||– 2 gigabytes (Hitachi)|
|2004||– 4 gigabytes|
|2005||– 6 gigabytes|
These drives fit into any CF II slot; however, they take more power 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.
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 reach 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.
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:
- Digital Camera
- Barcode scanner
- Magnetic stripe reader
- Super VGA port
- readers for various Flash media
- GBA Movie Player
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