CompactFlash (CF) is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain 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 the most successful of the early memory card formats, surpassing Miniature Card, SmartMedia, and PC Card Type I in popularity. Subsequent formats, such as SD/MMC, various Memory Stick formats, and xD-Picture Card offered stiff competition. Most of these cards are smaller than CompactFlash while offering comparable capacity and speed. Proprietary memory card formats for use in professional audio and video, such as P2 and SxS, are physically larger, faster, and more costly.

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, such as the Hasselblad CFV Digital Back for the Hasselblad series of medium format cameras. 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.

CompactFlash was originally built around Intel’s NOR-based flash memory, but has switched to NAND technology.[9] CF is among the oldest and most successful formats, and has held a niche in the professional camera market especially well. It has benefited from both a better cost to memory-size ratio than other formats, (for much of its life) and generally from greater available capacity 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 to 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 that 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.

CompactFlash interface is a 50 pin subset of the 68 pin PCMCIA connector. “It can be easily slipped into a passive 68-pin PCMCIA Type II to CF Type I adapter that fully meets PCMCIA electrical and mechanical interface specifications.” The Compactflash interface operates, depending on the state of a mode pin on powerup, as either 16-bit PC Card (0x7FF address limit) or as an IDE (PATA) interface.

CompactFlash IDE mode defines an interface that is smaller than, but electrically identical to, the ATA interface. That is, it appears to the host device as if it were a hard disk. The CF device contains an ATA controller. CF devices operate at 3.3 volts or 5 volts, and can be swapped from system to system. CompactFlash supports C-H-S and 28-bit Logical block addressing (CF 5.0 introduced support for LBA-48). CF cards may be set to master or slave, but have issues sharing the IDE bus. 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.

NOR-based flash has lower density than newer NAND-based systems, and CompactFlash is therefore the physically largest of the three memory card formats introduced in the early 1990s, being derived from the JEIDA/PCMCIA Memory Card formats. The other two are Miniature Card (MiniCard) and SmartMedia (SSFDC). However, CF did switch to NAND type memory later. The IBM Microdrive format implements the CF Type II interface, but is not solid-state memory. Hitachi and Seagate also make microdrives.

CompactFlash IDE (ATA) emulation speed is usually specified in “x” ratings, e.g. 8x, 20x, 133x. This is the same system used for CD-ROMs and indicates the maximum transfer rate in the form of a multiplier based on the original audio CD data transfer rate, which is 150 kbyte/s.

R = K * 150 kbyte/s

where R = transfer rate, K = speed rating. For example, 133x rating means transfer speed of: 133 * 150 kbyte/s = 19,950 kbyte/s ~ 20 Mbyte/s.

These are manufacturer speed ratings. Actual transfer speed may be higher, or lower, than shown on the card depending on several factors.

For reads, the onboard controller first powers up the memory chips from standby. Reads are usually in parallel, error correction is done on the data, then transferred through the interface 16 bits at a time. Error checking is required due to soft read errors. Writes require powerup from standby, wear leveling calculation, a block erase of the area to be written to, ECC calculation, write itself (an individual memory cell read takes around 100 ns, a write to the chip takes 1ms+ or 10,000 times longer).

Since the USB 2.0 interface is limited to 60 Mbyte/s and lacks bus mastering hardware, USB implementation results in slower access.

A direct motherboard connection is often limited to 33 Mbyte/s because IDE to CF adapters lack high speed ATA (66 Mbyte/s plus) cable support. Power on from sleep/off takes longer than power up from standby.

Microdrives are tiny hard disks—about 25 mm (1 inch) wide—packaged with a CompactFlash Type II form factor and interface. They were developed and released in 1999 by IBM with a capacity of 170 Mbyte. IBM sold its disk drive division, including the Microdrive trademark, to Hitachi in December 2002. There are now other brands of Microdrives (such as Seagate, Sony, etc.), and, over the years, these have become available in increasing capacities (up to 8 GB as of late 2008).

While these drives fit into and work in any CF II slot, the early versions drew more current (500 mA maximum) than flash memory (100 mA maximum). However current Microdrives use less than 200 mA for reads and writes (300 mA peak), and some flash devices used for high speed data e.g. Readyboost (memory can’t power down to standby) draw more than the USB standard allows (500 mA). As they are mechanical devices, Microdrives are susceptible to damage from physical shock or temperature changes. However, Microdrives are not subject to the write cycle limitation inherent to flash memory.

The iPod mini, Nokia N91, iriver H10 (5 or 6 GB model), PalmOne LifeDrive, and Rio Carbon all used a CF Microdrive to store data.

* CF cards are considered more rugged and durable to many “in the field” photographic shocks, impacts and accidents. CompactFlash cards are capable of withstanding more physical damage in comparison to other, flimsier designs.

* Due to their compatibility with IDE/ATA they are used in many embedded systems as solid-state drives. In early 2008 the CFA demonstrated CompactFlash cards with a built in SATA interface. Several companies make adapters to allow CF cards to be connected to PCI, IDE, 44-pin laptop mini-IDE, and SATA connections, allowing a CF card to act as a solid-state drive with virtually any operating system or BIOS, and even in a RAID configuration.

* CompactFlash does not have any built in DRM or cryptographic features like on some USB flash drives and other card formats. The lack of such features contributes to the openness of the standard since other memory card standards with such features are subject to restrictive licensing agreements.
* CF cards are available at higher storage capacities than some smaller flash memory cards.[weasel words]

* CompactFlash lacks the mechanical write protection switch that some other devices have, as seen in a comparison of memory cards.

* In the case of improper insertion, a card can potentially cause damage to the device receiving the card. However, this rarely happens[weasel words] as slots are usually designed to prevent this.

* CompactFlash’s large dimensions in comparison to other cards limits its feasibility in very slim devices. The large card slot consumes valuable internal space of the device, especially in point and shoot digital cameras. In its favour, a CompactFlash card cannot be lost as easily as a tiny MicroSD card, and insertion and removal may be easier with a larger card.

The marketplace for CompactFlash is extensive and includes counterfeits. Off-brand or counterfeit cards may be mislabeled, might not contain the actual amount of memory their controllers report to the host device, and may use types of memory that are not rated for the number of erase/rewrite cycles that the purchaser expects.

Since CompactFlash interface is electrically identical to the 16-bit PC card, the CompactFlash form factor is also used for a variety of Input/Output and interface devices; many standard PC cards have CF counterparts, some examples include:

* Ethernet
* Bluetooth
* Modem and GSM Modem, including GPRS and EDGE
* Wi-Fi
* Digital Camera
* Barcode scanner
* Magnetic stripe reader
* Super VGA display adapter
* Serial port and USB 1.1 host adapters
* readers for various other Flash media

CompactFlash card manufacturers

* Alcotek
* Apacer
* Cactus-tech
* Canon
* e c o SolidStateDrive Corporation
* FujiFilm
* Hitachi Maxell
* Kingston Technology
* Kodak
* Lexar
* Memorex
* Olympus
* Panasonic
* Ritek
* SanDisk
* Samsung
* Silicon Power
* Sony
* Swissbit
* Toshiba
* Transcend
* TwinMOS
* Verbatim Corporation

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