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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.[3] The physical format is now used for a variety of devices. CompactFlash became 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 after the introduction of CompactFlash, such as SD/MMC, various Memory Stick formats, xD-Picture Card, offered stiff competition. Most of these cards are significantly smaller than CompactFlash while offering comparable capacity and read/write speed. Professional memory cards, such as P2 and SxS, are physically larger, faster, and significantly more expensive. CompactFlash remains popular, and even has even experienced something of a comeback, caused by improvements in the ATA interface. For example, in 2008 Sony chose CompactFlash as the recording media for the HVR-MRC1K on-camera tapeless recording unit, instead of using smaller MemoryStick cards or expensive SxS cards.[4]
[edit] 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, such as the Hasseblad CFV Digital Back for the Hasseblad 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 it has switched over to NAND.[5] 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 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. 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. [edit] Technical details NOR-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 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. 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. [edit] SpeedFlash memory devices are non-volatile and solid-state, and thus 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.[6] 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.
[edit] Capacities and compatibility
As of 2008[update], CompactFlash cards are generally available in capacities from about 512 MiB to 100 GiB, with perhaps the most popular choices in Europe and North America being between 1 GiB and 16 GiB. The CF Specification can support capacities up to 137 GB (128 GiB). Lower capacity cards, below 512 MiB, 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 64 GiB models from various manufacturers — SanDisk launched its 16 GiB Extreme III card at the 2006 Photokina trade fair, Transcend announced its 32 GiB card on January 15, 2008.[7] Samsung launched 16, 32 and 64 GiB CF cards soon after. Pretec announced 48 GiB cards in January 2008 and 100GB cards in September.[8][9][10] Pretec, Transcend and Sandisk introduced 64 GiB cards in August/September 2009. These cards, and almost all cards over 2 GiB, require that the host device support the FAT32 file system (if the camera is using a FAT file system). The largest cards, however, are usually not the fastest. [edit] FilesystemsThere are varying levels of compatibility among FAT32-compatible cameras. While any camera that claims FAT32-capability should 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 to apply a FAT32 format. The way many digital cameras update the files system as they write to the card creates a FAT32 bottleneck. 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 writes the same photo to a FAT16-formatted 2 GiB CompactFlash card somewhat faster than to a same speed 4 GiB FAT32-formatted CompactFlash card, although the memory chips in both cards have the same write speed specification.[11] 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. [edit] CF+ and Compact Flash specification revisionsWhen 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 (128 GiB). While the current revision 4.1 as of 2007-03-02 works only in [P]ATA mode, future revisions are expected to implement SATA.
[edit] CFastA future version of CompactFlash, known as CFast, is based on the Serial ATA bus, rather than the Parallel ATA/IDE bus all previous versions of CompactFlash are designed for. These cards will support a higher maximum transfer rate than current CompactFlash cards. As of 2009[update], 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,[12] 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.[13] At CES 2009, Pretec showed a 32 GB CFast and announced that they should reach market within a few months.[14] [edit] Type I and Type IIThe 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.[15] 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.[16][17] 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 that support mainly type I slots. Some of the latest DSLRs, like the Nikon D700 and D300s, have also dropped Type II support.[citation needed] [edit] Microdrives Main 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 GiB 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). As they are mechanical devices, Microdrives are more susceptible to damage from physical shock or temperature changes than flash memory. However, 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. [edit] Compared to other portable storage
[edit] CounterfeitingThere 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 that are not intended for extensive rewriting.[20][21] [edit] 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:
[edit] CompactFlash card manufacturers
[edit] See also[edit] References
[edit] External links
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