CompactFlash (CF) is a mass storage device format used in portable electronic devices. For storage, CompactFlash typically uses flash memory in a standardized enclosure.

The format was first specified and produced by SanDisk in 1994. The physical format is now used for a variety of devices.

CompactFlash became a popular storage medium for digital cameras. In recent years it has been widely replaced by smaller cards on the consumer end, but it is still a preferred format for D-SLR cameras, for its superior capacity and reliability.

Description

There are two main subdivisions of CF cards, Type I (3.3 mm thick) and the thicker Type II (CF2) cards (5 mm thick). The CF Type II slot is used by Microdrives and some other devices. There are four main speeds of cards including the original CF, CF High Speed (using CF+/CF2.0), a faster CF 3.0 standard and a yet faster CF 4.0 standard that is being adopted as of 2007. The thickness of the CF card type is dictated by the preceding PC Card standard which was used for data storage in previous years.

CompactFlash was originally built around Intel's NOR-based flash memory, but it has switched over to NAND. CF is among the oldest and most successful formats, and has held to a niche in the professional camera market especially well. It has benefited from having both a better cost to memory-size ratio than other formats for much of its life, and generally from having available capacities larger than other formats.

CF cards can be used directly in a PC Card slot with a plug adapter, used as an ATA (IDE) or PCMCIA storage device with a passive adapter or with a reader, or attached various other types of ports such as USB or FireWire. As some newer card types are smaller, they can be used directly in a CF card slot with an adapter. Formats which can be used this way include 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.

Flash memory, regardless of format, can take only a limited number of erase/write cycles to a particular "block" before that block can no longer be written. Typically, the controller in a CompactFlash device attempts to prevent premature wear out of a sector by choosing the location for a piece of data at write time so as to spread out the writing over the device. This process is called wear leveling.

When using CompactFlash in ATA mode as a hard drive replacement, wear leveling becomes critical. The advanced CompactFlash controllers spread the wear-leveling across the entire drive allowing all blocks to participate. The even more advanced CompactFlash controllers will also move the data that is rarely changed so that all blocks are worn evenly.

Technical details