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 has even experienced something of a comeback. For example, in 2008 Sony chose CompactFlash as the recording media for use in the HVR-MRC1K tapeless video recorder instead of using smaller MemoryStick cards or expensive SxS cards.^[4] In 2010 Canon chose CompactFlash as the recording media for use in the XF300 and XF305 high definition video cameras.^[5]

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 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 it has switched over to NAND.^[6] 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.

Technical details

CompactFlash interface is a 50 pin subset of the 68 pin PCMCIA^[7] 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."^[8] 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.^[9] Compactflash supports C-H-S and 28-bit Logical Block Addressing. CF cards may be set to master or slave, but have issues sharing the IDE bus.

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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, being derived from the JEIDA/PCMCIA Memory Card formats. 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. Hitachi and Seagate also make microdrives.

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. 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.

Speed

Speed is a function of several factors.

CompactFlash — Flash Memory: 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 errors on read. 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 chip read takes around 100 ns, a write to the chip takes 1ms+ or 10,000 times longer). As the USB 2.0 interface is limited to 60 MB/sec, as well as lack of bus mastering in the hardware USB implementation will result in slower access. Direct motherboard connection is often limited to 33 MB/sec because IDE to CF adapters lack high speed ATA (66 MB/sec plus) cable support. Power on from sleep/off takes longer than power up from standby.

Compact Flash — Magnetic Media: Many 1-inch (25 mm) hard drives 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^[10] 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 MB/s read and write, and has an interface speed of 33 MB/sec. Hitachi's 4 GB Microdrive is 12 ms seek, sustained 6 MB/sec.

Flash memory devices are non-volatile and solid-state, and thus are as robust or more so than magnetic media disk drives. The ST68022CF Microdrive is only rated to 175 G operating and 750 G non-operating shock. Small 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.^[11] Manufacturers warning on flash memory used for ReadyBoost indicates using over 500 mA.

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 multiplier of the data rate of an audio CD, which is 150 KB/s.

$R\; =\; \{K\; \backslash cdot\; 150\}$, KB/sec

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

These are manufacturer speed ratings and actual transfer speed may be higher, or sometimes lower, than that shown on a card.^[12]

Capacities and compatibility

Since flash memory is generally produced in capacities that are multiples of powers of 2, IEC standard binary prefixes are used throughout this article.

As of 2008^[update], CompactFlash cards are generally available in capacities from about 64 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 (support 28 bit LBA) 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.^[13] Samsung launched 16, 32 and 64 GiB CF cards soon after. Pretec announced 48 GiB cards in January 2008 and 100GB cards in September.^[14][15][16] 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).

Reliability

An important consideration for use in systems is reliability. The original PC Card memory cards were battery backed RAM then NOR flash. At the time NOR flash had a write endurance of 10,000 cycles (but no read liability). The currently used NAND^[17] flash has an endurance of 1,000,000 writes^[17] per location (less reliable than magnetic media) before hard failure and is prone to frequent soft errors on read.^[18] The CompactFlash card includes error checking and correction (ECC) and wear leveling circuitry that is transparent to the data user, although it may slow data access. The book "Car PC Hacks" suggest disabling Windows swap file and using EWF (Enhanced Write Filter) to eliminate unnecessary writes to CF storage media. However, EWF is available only in XP Embedded operating system, not XP Professional, Home, or Media Edition.

Filesystems

Originally, flash memory used Flash File System and JFFS to work around low level issues with the technology. Since hardware now hides much of the complexity from the end user, Compactflash disk storage for use in consumer devices is formatted as FAT or FAT32 which not only works with end user computers but also is simple enough for limited processing ability of processors in devices such as Cameras.

These hardware issues still surface to limit performance.^[19] The exFAT format (successor to Flash File System) is more compatible with the way flash memory works.

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 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 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.^[20] Although Fat16 is more wasteful of disk space with its larger clusters, it works better with the write strategy that flash memory chips require.^[19] A Microdrive would not have any difference because writes are to 512 byte sectors.^[19]

The cards themselves can of course be formatted with any type of file system such as 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 can be used to obtain faster seek times than hard drives.

CF+ and Compact Flash 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 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.

• CompactFlash Revision 1.0 (1995), 8.3 MB/s (PIO mode 2), support for up to 128 GiB (137 GB) storage space.

• CompactFlash+ aka CompactFlash I/O (1997)

• CF+ and CompactFlash Revision 2.0 (2003) added an increase in speed to 16.6 MB/s data-transfer (PIO mode 4). At the end of 2003, DMA 33 transfers were added as well, available since mid 2004.

• CF+ and CompactFlash Revision 3.0 (2004) added support for up to a 66 MB/s data transfer rate (UDMA 66), 25 MB/s in PC Card mode, added password protection, along with a number of other features. CFA recommends usage of the FAT32 filesystem for storage cards larger than 2 GiB.

• CF+ and CompactFlash Revision 4.0 (2006) added support for IDE Ultra DMA 133 for a maximum data transfer rate of 133 MB/s (UDMA 133).

• CF+ and CompactFlash Revision 4.1 (2007) added support for Power Enhanced CF Storage Cards.

• CompactFlash Revision 5.0 (2010) added a number of features, including 48-bit addressing (supporting 128 Petabyte of storage), larger block transfers up to 32 Megabytes, quality-of-service and video performance guarantees, and other enhancements ^[21]

CE-ATA

CE-ATA is a Serial ATA interface based on the MultiMediaCard standard.^[22][23]

CFast

A variant 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 support a higher maximum transfer rate than current CompactFlash cards. As of 2009^[update], SATA (SATA II) 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 devices support speeds greater than 133 MB/s, but when enough are teamed together in parallel, they can exceed 300 MB/s. CFast cards are not physically or electrically compatible with CF cards, requiring new card readers and new digital cameras to take advantage of them. However, since SATA can emulate PATA on the software side, CFast cards don't require new driver software in operating systems, but 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,^[24] so an adaptor will be required to connect CFast cards in place of standard SATA hard drives.

First CFast cards have reached the market in late 2009.^[25] At CES 2009, Pretec showed a 32 GB CFast and announced that they should reach market within a few months.^[26]

Type I and Type II

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.^[27] 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 can draw up to 500 mA.

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.^[28][29] 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 4 GB 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, have also dropped Type II support.^[30]

Microdrives

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, many years ago they 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) more than USB standard allows (500 mA). 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 iPod mini, Nokia N91, iriver H10 (5 or 6 GB model), PalmOne LifeDrive, 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.^{[citation needed]}

• 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.^[31] Several companies make adapters to allow CF cards to be connected to PCI, IDE, 44-pin laptop mini-IDE, and SATA connections,^[32] 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 [2]

• 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. On another hand, a CompactFlash card cannot be lost as easily as a tiny MicroSD card, and insertion and removal may be easier with a larger card.

Counterfeiting

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 that are not intended for extensive rewriting.^[33][34]

Other devices in the CF form factor

Since CompactFlash interface is electrically identical to the 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
• 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

• A-DATA
• ATP
• Apacer
• Canon
• FujiFilm
• Hitachi Maxell
• Kingston Technology
• Kodak
• Lexar
• Memorex
• Olympus
• Panasonic
• PNY
• PQI
• Ritek
• SanDisk
• Samsung
• Silicon Power
• Sony
• Swissbit
• Toshiba
• Transcend
• Verbatim Corporation
• UMAX

See also

• Comparison of memory cards
• Microdrive
• PC Card
• ExpressCard
• Random access memory

References

External links

• CompactFlash Association
• Rob Galbraith DPI: CF Performance Database
• CompactFlash connector description and pin layout
• CompactFlash pinout
• CompactFlash Connector Schematic and complete Pinout
• Compact Flash Disassembly Photos