A 2 GB CompactFlash card
|Media type||Mass storage device format|
|Encoding||Various file systems|
|Capacity||2 MiB to 128 GiB(CF5.0: up to 128 PiB)|
|Dimensions||43×36×3.3 mm (Type I) 43×36×5 mm (Type II)|
|Weight||10 gram (typical)|
|Usage||Digital cameras and other mass storage devices|
|Extended from||PCMCIA / PC Card|
CompactFlash (CF) is a mass storage device format used in portable electronic devices. The format was first specified and produced by SanDisk in 1994. It is now used for a variety of devices; most contain flash memory but some, such as the Microdrive, contain a hard disk.
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 MMC/SD, 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 costlier.
CompactFlash remains popular and is even supported in some new devices. For example, in 2008, Sony chose CompactFlash as the recording medium for the HVR-MRC1K tapeless video recorder over smaller MemoryStick cards or expensive SxS cards. In 2010, Canon chose CompactFlash as the recording medium for its new professional high-definition video cameras, and Ikegami devices record digital video onto CompactFlash cards through an adaptor.
In November 2010, Sandisk, Sony and Nikon proposed a next generation card format to the CompactFlash Association which would come in a similar form factor as CF/CFast but be based on PCI Express instead of Parallel ATA or SATA. The new format is targeted at high-definition camcorders and high-resolution digital photo cameras, would offer a target read and write speeds of 1 Gbit/s (125 Mbyte/s) and storage capabilities beyond 2 TiB, and is not backward compatible with either CompactFlash or CFast. The XQD card format has been announced by the CompactFlash Association in December 2011.
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. 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.
The 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", according to compactflash.org. The interface operates, depending on the state of a mode pin on power-up, as either a 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. The CF device contains an ATA controller and appears to the host device as if it were a hard disk. 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 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.
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. The speed rating quoted is almost always the read speed, write speed is often slower.
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).
Because 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.
Many 1-inch (25 mm) hard drives (often referred to by the trademarked name "Microdrive") typically spin at 3600 rpm so rotational latency is a consideration, as is spin-up from standby or idle. Seagate's 8 GB ST68022CF drive spins up fully within a few revolutions but power draw can reach up to 350 milliamps and runs at 40-50 mA average power. Its average seek time is 8 ms and can sustain 9 Mbyte/s read and write, and has an interface speed of 33 Mbyte/s. Hitachi's 4 GB Microdrive is 12 ms seek, sustained 6 Mbyte/s.
The CF Specification supports capacities up to 137 GB using 28-bit logical block addressing (LBA). Prior to 2006, CF drives using magnetic media offered the highest capacities (up to 8 GiB). Now there are solid-state cards with higher capacities (up to 64 GiB).
As of 2011, solid-state drives (SSDs) have supplanted both kinds of CF drive for large capacity requirements.
SanDisk announced its 16 GiB Extreme III card at the Photokina trade fair, in September, 2006. That same month, Samsung announced 16, 32 and 64 GiB CF cards. Two years later, in September, 2008, PRETEC announced 100GB cards.
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, PCMCIA, 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.
CF cards may perform the function of the master or slave drive on the IDE bus, but have issues sharing the bus. Moreover, late-model cards that provide DMA (using UDMA or MWDMA) may present problems when used through a passive adapter that does not support DMA.
Original PC Card memory cards used an internal battery to maintain data when power was removed; the rated life of the battery was the only reliability issue. CompactFlash cards that use flash memory, like other flash-memory devices, are rated for a limited number of erase/write cycles for any "block." (Read cycles do not cause wear to the device.) Cards using NOR flash had a write endurance of 10,000 cycles. Current cards using NAND flash are rated for 1,000,000 writes per block before hard failure. This is less reliable than magnetic media. Car PC Hacks suggests disabling the Windows swap file and using its Enhanced Write Filter (EWF) to eliminate unnecessary writes to flash memory. Additionally, when formatting a flash-memory drive, the Quick Format method should be used, as one need not write every block on the drive, as may be necessary for a new magnetic disk.
Most CompactFlash flash-memory devices limit wear on blocks by varying the physical location to which a block is written. This process is called wear leveling. When using CompactFlash in ATA mode to take the place of the hard disk drive, wear leveling becomes critical because low-numbered blocks contain tables whose contents change frequently. Current CompactFlash cards spread the wear-leveling across the entire drive. The more advanced CompactFlash cards will move data that rarely changes to ensure all blocks wear evenly.
NAND flash memory is prone to frequent soft read errors. The CompactFlash card includes error checking and correcting (ECC) that detects the error and re-reads the block. The process is transparent to the user, although it may slow data access.
As flash memory devices are solid-state, they are more shock-proof than rotating disks. For example, the ST68022CF Microdrive is shock rated at 175G operating and 750G non-operating.
The possibility for electrical damage from upside-down insertion is prevented by asymmetrical side slots, assuming that the host device uses a suitable connector.
Small cards consume around 5% of the power required by small disk drives and still have reasonable transfer rates of over 45 Mbyte/s for the more expensive 'high-speed' cards. However, the manufacturer's warning on the flash memory used for ReadyBoost indicates a current draw in excess of 500 mA.
Originally, flash memory used Flash File System and JFFS to work around low-level technical issues. Hardware now hides much of the complexity from the end user, and CompactFlash cards for use in consumer devices are typically formatted as FAT12 (for media up to 16 MiB), FAT16 (for media up to 2 GiB, sometimes up to 4 GiB) and FAT32 (for media larger than 2 GiB). This lets the devices be read by personal computers but also suits the limited processing ability of some consumer devices such as cameras.
There are varying levels of compatibility among FAT32-compatible cameras, MP3 players, PDAs, and other devices. While any device that claims FAT32-capability should read and write to a FAT32-formatted card without problems, some devices 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 file 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 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. Although FAT16 is more wasteful of disk space with its larger clusters, it works better with the write strategy that flash memory chips require.
The cards themselves can of course be formatted with any type of file system such as Ext, JFS and NTFS. It 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 often have faster seek times than hard drives.
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 manufactured after the original Revision 1.0 specification are available in capacities up to 128 GiB. While the current revision 6.0 works in [P]ATA mode, future revisions are expected to implement SATA mode.
CFast cards are not physically or electrically compatible with CompactFlash cards. However, since SATA can emulate the PATA command protocol, existing CompactFlash software drivers can be used, although writing new drivers to use AHCI instead of PATA emulation will almost always result in significant performance gains. 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 is required to connect CFast cards in place of standard SATA hard drives.
The first CFast cards reached the market in late 2009. At CES 2009, Pretec showed a 32 GB CFast and announced that they should reach the market within a few months. Delock began distributing CFast cards in 2010 and offers several card readers with USB3.0 port and eSATAp (power over eSATA) port to support CFast cards.
The only physical difference between the two types is that Type I devices are 3.3 mm thick while Type II devices are 5 mm thick. Electrically, the two interfaces are the same except that Type I devices are permitted to draw up to 70 mA supply current from the interface, while type II devices may draw up to 500 mA.
Most Type II devices are Microdrives (see below), other miniature hard drives, and adapters, such as a popular adapter that takes Secure Digital cards. A few flash-based Type II devices were manufactured, but Type I cards are now available in capacities that exceed Microdrives. Manufacturers of CompactFlash cards such as Sandisk, Toshiba, Alcotek and Hynix offer devices with Type I slots only. Some of the latest DSLR cameras, like the Nikon D800, have also dropped Type II support.
Microdrives are tiny hard disks—about 25 mm (1 inch) wide—in a CompactFlash Type II package. The first was 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 2002. Comparable hard disks were also made by other vendors, such as Seagate and Sony. They are available in capacities of up to 8 GB.
As Microdrives are mechanical devices, they draw more current than flash memory (100 mA maximum). Early versions drew up to 500 mA, but more recent Microdrives draw under 200 mA for reads and under 300 mA for writes. (Some devices used for high speed—such as Readyboost, which has no low-power standby mode—exceed the 500 mA maximum of the Type II standard.) Microdrives are also susceptible to damage from physical shock or temperature changes. However, Microdrives typically have a longer lifespan of write cycles than flash memory.
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:
|Wikimedia Commons has media related to: CompactFlash|
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