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Compact Flash

CompactFlash, often labled simply CF, is a variety of flash memory encased in a standard-sized enclosure used in many portable electronic devices. It was the first such flash memory standard, built around Intel's NOR-based flash memory. NOR-based flash has lower density than newer NAND-based systems, and Compact Flash is therefore (in spite of its name) much larger than competing standards like MMC or Memory Stick.

Compact Flash defines a smaller interface based on the PCMCIA-ATA interface. That is, it appears to devices as if it were a hard drive of some defined size. The connector is about 2cm across, and the case comes in two standard sizes, CF I at 3.3mm thick, and CF II at 5mm thick. Both are otherwise identical. IBM also builds full hard drive systems that fit into the CF II format, the MicroDrive.

They are non-volatile and solid state, thus more durable than disk drives, and consume around 5% of the power required by small disk drives. They operate at 3.3V & 5V power levels, and can be swapped from system to system. CF cards are able to cope with extremely rapid changes in temperature. Industrial versions of CF cards can operate at a range of -45C to +85C.

Used most often in palm devices (which won't take larger form-factor cards), digital cameras, and a wide variety of other uses, including desktop machines.

CF+ specification

When Compact Flash was first being standardized, even hard drives were rarely larger than 4GB in size, and so the existing limitations of the ATA standard were considered acceptable. Since then hard drives 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 limits.

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 16MB/sec data-transfer, and capacities up to 137GB.

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