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CompactFlash

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CompactFlash
A 64 MB CompactFlash Type I card
Capacity2MB to 64GB
Developed bySanDisk
Dimensions43x36x3.3mm (Type I) 43x36x5mm (Type II)
Weight10 grammes (typical)
UsageHigh-end cameras, SSD's
A 16GB CompactFlash card installed in an IDE port with adaptor

CompactFlash (CF) was originally developed as a type of data storage device used in portable electronic devices. For storage, CompactFlash typically uses flash memory in a standardized enclosure. This form was first specified and produced by SanDisk in 1994. The physical format is now used for a variety of devices.

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. 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 PCMCIA card type standard.

CF was among the first flash memory standards to compete with the earlier and larger PC card Type I memory cards, and was originally built around Intel's NOR-based flash memory, though it switched over to NAND. CF is among the oldest and most successful formats, and has held on to a niche in the professional camera market especially well. It has benefited from having both a good cost to memory size ratio relative to other formats for much of its life, and generally having larger capacities available than smaller formats.

CF cards can be used directly in PC Card slot with a plug adapter, used as an IDE hard drive with a passive adapter, and with a reader, to any number of common ports like USB or FireWire. As it has a bigger size relative to the smaller cards that came later, many other formats can be used directly in a CF card slot with an adapter (including 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, supports only a limited number of erase/write cycles before a particular "sector" can no longer be written. Memory specifications generally allow 10,000[1] to 1,000,000 write cycles. Typically the controller in a CompactFlash attempts to prevent premature wearout of a sector by mapping the writes to various other sectors in the card - a process referred to as wear levelling.

Technical details

Loading a CF card into the Canon Powershot A95
1 GB CF card into a Nikon D200 DSLR camera

NOR-based flash has lower density than newer NAND-based systems, and CompactFlash is therefore the largest of the three memory card formats that came out in the early 1990s, the other two being Miniature Card (MiniCard) and SmartMedia (SSDFC). However, CF did switch to NAND type memory later on. The IBM Microdrive format, which used CF Type II, was 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 of some defined size and has a tiny IDE controller onboard the CF device itself.

CF cards are much more compact than the even earlier PC card (PCMCIA) Type I memory cards, except for its thickness which matches PC Card Type I and Type II thicknesses respectively. CF has managed to be the most successful of the early memory card formats, outliving both Miniature Card, SmartMedia, and PC Card Type I in mainstream popularity. SmartMedia did offer heavy competition to CF in smaller devices, and was more popular than CF at its peak in terms of market penetration, but SmartMedia would cede this area to newer card types (during the period of roughly 2002-2005).

The memory card formats that came out in the late 1990s to 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 dominate the memory card market for PDAs, cell phones, and consumer cameras (especially subcompact models).

However, a CF interface continues to be offered on many devices, and remains the main standard for professional cameras, as well as a number of consumer models as of 2005. Key features remain having a relatively low cost per megabyte, offering a greater capacity than smaller cards, the ability for the CF II to use MicroDrive, and the availability of adaptors which allow many other smaller card formats to be used in a CF slot. And CF cards can also be used in PC Card slots with very inexpensive plug adapters.

CF (and other formats) have not managed to totally replace PC Card Type I and II Memory cards in a number of industrial applications.

Flash memory devices are non-volatile and solid state, and thus are more robust than disk drives, and consume around 5% of the power required by small disk drives, and yet still have good transfer speeds (up to 40 MB/s write and 40 MB/s read for the SanDisk Extreme IV). Card speed is often specified in times ratings, i.e. 8x, 20x, 133x..., (the same system as used for CD-ROM's) where the number in front of 'x' when multiplied by 150kB/s gives the speed of the card (for example, 20x = 3.0MB/s). They 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 devices are used in handheld and laptop computers (which may or may not take larger form-factor cards), digital cameras, and a wide variety of other devices, including portable audio recorders and desktop computers.

Capacities and compatibility

As of 2007, CompactFlash cards are generally available in capacities from about 512 MB to about 64 GB, with perhaps the most popular choices in Europe and North America being between 512 MB and 8 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 16 GB models from various manufacturers — SanDisk launched its 16 GB Extreme III card at the 2006 Photokina trade fair. Samsung has launched 16, 32 and 64 GB CF cards however these are not sold under the Samsung brand. These cards, indeed, almost all cards over 2 GB, require the host camera to support the FAT32 file system, if the camera is using a FAT file system. These largest cards, however, are not the fastest.

There are different levels of compatibility amongst FAT32-compatible cameras. While any camera that claims 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.[2]

The cards themselves can of course be formatted with any type of filesystem 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 PC's 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, however this is only true for CompactFlash cards supporting Direct memory access

CF+ specification

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. Since then hard disks have had to make many modifications to the ATA system to handle ever-growing media, and today even flash memory cards have been able to pass the 4 GB limit. However, CF cards since the original Revision 1.0 have been able to support capacities up to 137 GB.

The CF+ standard, revision 2.0, added an increase in speed to 16 MB/s data-transfer, according to the CompactFlash Association (CFA).

The newer CF 3.0 standard supports up to a 66 MB/s data transfer rate, along with a number of other features. The even newer CF 4.0 standard supports IDE Ultra DMA 133 for a maximum data transfer rate of 133 MB/s.

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Type I and Type II

The only difference between the two types is that the Type II devices are 5mm thick while Type I devices are 3.3mm thick.[3] 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. [4][5] Even the largest capacity cards commonly available are Type I cards and most card readers will read both formats with the exception of some early CF based cameras where the slot is too small and some of the poorer quality USB card readers with the same problem.

Microdrives

IBM 1 GB Microdrive
Main article: Microdrive

Microdrives are tiny hard disks—about 25 mm (1") 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. The division was then sold to Hitachi in December 2002 along with the Microdrive trademark. There are now other brands that sell Microdrives (such as Seagate, Sony, etc), and, over the years, these have become available in increasingly larger capacities (up to 8 GB as of August 2007).

While these drives fit into any CF II slot, they draw more current on average (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 they are more sensitive to physical shock and temperature changes than flash memory.

The popular iPod mini and the Rio Carbon are devices which uses a compact Microdrive to store music.

Compared to other portable storage

Strengths

CompactFlash cards are considered the main form of flash storage for almost all major Professional Photographic needs. All major camera brands such as Canon, Fuji, Nikon, Olympus and Sony use this form of flash storage in almost all their 'Pro Cameras'. In comparison to other card formats, CompactFlash has remained the longest and most consistent performer, (in terms of industry standards). CF cards are also considered far 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] That is why most professional photographers and photojournalists prefer to use it.[citation needed]

Due to their compatibility with IDE/ATA they are used in many embedded systems as solid-state drives.

CompactFlash does not have any built in DRM or cryptographic features like on some USB flash drives and other formats such as Secure Digital. 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.

Weaknesses

  • In the case of improper insertion, a card can potentially cause damage to a receptor device. The consequence of which may result in an expensive repair. However this rarely happens and slots are usually designed to prevent this from happening.

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 which are not intended for extensive rewriting. [6][7]

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:

Compact Flash card manufacturers

See also

References

  1. ^ http://www.atmel.com/dyn/resources/prod_documents/2503S.pdf
  2. ^ http://www.robgalbraith.com/bins/content_page.asp?cid=7-6453-6837
  3. ^ http://www.compactflash.org/faqs/faq.htm#What_is
  4. ^ http://www.dpreview.com/news/9911/99112302delkin224.asp
  5. ^ http://www.letsgodigital.org/en/news/articles/story_934.html
  6. ^ http://reviews.ebay.ie/FAKE-SanDisk-Extreme-Compact-Flash-Cards-Exposed_W0QQugidZ10000000001456526
  7. ^ http://www.pictureline.com/newsletter/article.php?id=401
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