What is a Compact Flash Memory Card?

A flash memory format introduced in 1994 by SanDisk Corporation, Milpitas, CA.  At 36.4 x 42.8 x 3.3 mm, CompactFlash (CF) cards are larger than other flash cards, but are popular storage in digital SLRs, which more easily accommodate their size than small point-and-shoot cameras..

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.

CompactFlash Card

A 64 MiB CompactFlash Type I card

Media type Mass storage device format
Encoding Various file systems
Capacity 2 MiB to 184 GiB
Developed by SanDisk
Dimensions 43×36×3.3 mm (Type I) 43×36×5 mm (Type II)
Weight 10 grams (typical)
Usage Digital cameras and other mass storage devices
Extended from PCMCIA / PC
A 16-GB CompactFlash card installed in a 2.5" IDE port with adaptorThere 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

1 GB CF card in a Nikon D200 DSLR cameraNOR-based flash has lower density than newer NAND-based systems, and CompactFlash is therefore the physically largest of the three memory card formats that came out in the early 1990s, the other two being Miniature Card (MiniCard) and SmartMedia (SSFDC). However, CF did switch to NAND type memory later on. The IBM Microdrive format implements the CF Type II interface, but is not solid-state memory.

CompactFlash defines a physical interface which 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. 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 has managed to be the most successful of the early memory card formats, outliving Miniature Card, SmartMedia, and PC Card Type I in mainstream popularity. The memory card formats that came out in the late 1990s through the early 2000s (SD/MMC, various Memory Stick formats, xD-Picture Card, etc.) offered stiff competition. The new formats were significantly smaller than CF, in some cases by an even greater fraction than CF had been smaller than PC Card. These new formats would eventually dominate the memory card market for compact consumer electronic devices.


Flash memory devices are non-volatile and solid-state, and As a result are more robust than disk drives. Cards consume around 5% of the power required by small disk drives and still have reasonable transfer rates of over 45 MB/s for the more expensive 'high speed' cards.

Card speed is usually specified in "x" ratings, e.g. 8x, 20x, 133x. This is the same system used for CD-ROMs and gives the data rate as a multiple of the data rate of the first CD-ROMs (i.e. the data rate of an audio CD). The base rate is 150 kB/s, so for example, 20x = 20 * 150 kB/s = 3.0 MB/s.

The following table lists some common ratings and their respective maximum transfer rates.

Rating Speed (MB/s)
  6x  0.9
 32x  4.8
 40x  6.0
 66x 10.0
100x 15.0
133x 20.0
150x 22.5
200x 30.0
266x 40.0
300x 45.0

Capacities and Compatibility

As of 2009, CompactFlash cards are generally available in capacities from about 512 MB to 100 GB, with perhaps the most popular choices in Europe and North America being between 1 GB and 16 GB. Lower capacity cards, below 512 MB, are becoming rare in stores as higher capacity cards are readily available at the same price. The largest CompactFlash cards commonly available currently are the 32 GB models from various manufacturers — SanDisk launched its 16 GB Extreme III card at the 2006 Photokina trade fair, Transcend announced its 32 GB card on January 15, 2008. Samsung launched 16, 32 and 64 GB CF cards soon after. Pretec announced 48 GB cards in January 2008 and 100GB cards in September. These cards, and almost all cards over 2 GB, require the host device to support the FAT32 file system (if the camera is using a FAT file system). The largest cards, however, are usually not among the fastest ones.


There are varying levels of compatibility among FAT32-compatible cameras. While any camera that is claimed to be FAT32-capable is expected to read and write to a FAT32-formatted card without problems, some cameras are tripped up by cards larger than 2 GB that are completely unformatted, while others may take longer time to apply a FAT32 format. For example, the FAT32-compatible Canon EOS-1Ds will format any unformatted card with FAT16, even ones larger than 2 GB.

Indeed, there is a FAT32 bottleneck because of the manner in which many digital cameras update the file system as they write photos to the card. Writing to a FAT32-formatted card generally takes a little longer than writing to a FAT16-formatted card with similar performance capabilities. For instance, the Canon EOS 10D will write the same photo to a FAT16-formatted 2 GB CompactFlash card somewhat faster than to a same speed 4 GB FAT32-formatted CompactFlash card, although the memory chips in both cards have the same write speed specification.

The cards themselves can of course be formatted with any type of file system such as JFS and can be divided into partitions as long as the host device can read them. CompactFlash cards are often used instead of hard drives in embedded systems, dumb terminals and various small form-factor PCs that are built for low noise output or power consumption. CompactFlash cards are often more readily available and smaller than purpose-built solid-state drives and can be used to obtain faster seek times than hard drives.

CF+ Specification Revisions

When CompactFlash was first being standardized, even full-sized hard disks were rarely larger than 4 GB in size, and so the limitations of the ATA standard were considered acceptable. However, CF cards since the original Revision 1.0 have been able to have capacities up to 137 GB. While the current revision 4.1 from 2004 works only in ATA mode, future revisions are expected to implement SATA.

  • Revision 2.0 added an increase in speed to 16 MB/s data-transfer, according to the CompactFlash Association (CFA).
  • Revision 3.0 supports up to a 66 MB/s data transfer rate, along with a number of other features.
  • Revision 4.0 supports IDE Ultra DMA 133 for a maximum data transfer rate of 133 MB/s.


A future version of CompactFlash, known as CFast, will be based on the Serial ATA bus, rather than the Parallel ATA/IDE bus for which all previous versions of CompactFlash are designed.

These cards will support a higher maximum transfer rate than current CompactFlash cards. As of 2009, SATA supports transfer rates up to 300 MB/s, while PATA is limited to 133 MB/s using UDMA 6. Few, if any, current flash memory device support speeds greater than 133 MB/s, and CFast cards will not be physically or electronically compatible with CF cards, requiring new card readers and new digital cameras to take advantage of them. CFast cards use a 7-pin SATA data connector (identical to the standard SATA connector), but a 17-pin power connector that appears incompatible with the standard 15-pin SATA power connector, so an adaptor will be required to connect CFast cards in place of standard SATA hard drives.

CFast cards are expected to reach market in late 2009. At CES 2009, Pretec showed a 32 GB CFast and announced that they should reach market within a few months.

Type I and Type II

The only difference between the two types is that the Type II devices are 5 mm thick while Type I devices are 3.3 mm thick. The vast majority of all Type II devices are Microdrives and other miniature hard drives. Flash based Type II devices are rare but a few examples do exist. Compact Flash - Secure Digital adapters usually are Type II. Even the largest capacity cards commonly available are Type I cards. Most card readers will read both formats, with the exception of some early CF based cameras or poorer quality USB card readers where the slot is too small. Various Manufacturers of 4GB Compact Flash cards such as Sandisk, Toshiba, Alcotek and Hynix have developed devices which support mainly type I slots. Some latest DSLR's also dropped Type II support.


IBM 1 GB MicrodriveMain article: Microdrive 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 in a 170 megabyte capacity. IBM then 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, they draw more current (500 mA maximum) than flash memory (100 mA maximum) and so may not work in some low-power devices (for example, NEC HPCs). Being a mechanical device a Microdrive is more sensitive to physical shock and temperature changes than flash memory. But Microdrives are not subject to the write cycle limitation inherent to flash memory.

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

Compared to Other Portable Storage

  • 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.
  • CompactFlash lacks the mechanical write protection switch that some other devices have, as seen in a comparison of memory cards with exception of industrial CF-card models (AC60 Turbo/ AC73 and AC75 series) made by CoreSolid Storage 
  • In the case of improper insertion, a card can potentially cause damage to the device receiving the card. However, this rarely happens 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 devices' valuable internal space, especially in point and shoot digital cameras.


There is extensive marketplace competition for sales of all brands of flash memory. As a result counterfeiting is quite widespread. Under their own brand, or while imitating another, unscrupulous flash memory card manufacturers may sell low-capacity cards formatted to indicate a higher capacity, or else use types of memory which are not intended for extensive rewriting.

Other Devices Conforming to the CF Standard

Various CF I/O cardsThe 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:

  • Ethernet
  • Bluetooth
  • Modem
  • Wi-Fi
  • Digital Camera
  • GPS
  • Barcode scanner
  • RFID
  • Magnetic stripe reader
  • Super VGA display adapter
  • Serial port and USB 1.1 host adapters
  • readers for various other Flash media

CompactFlash Card Manufacturers

  • Apacer
  • A-DATA
  • ATP
  • Canon
  • FujiFilm
  • Kingston Technology
  • Kodak
  • Lexar
  • Memorex
  • Olympus
  • Panasonic
  • PNY
  • Red Digital Cinema
  • Ritek
  • Sandisk
  • Samsung
  • Sony
  • Toshiba
  • Transcend
  • Verbatim Corporation
  • UMAX
  • WinSystems Industrial Grade

See also

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