Compact Flash Digital Camera Memory Cards

CompactFlash (CF) was originally developed by Sandisk in 1994 and is the worlds most popular type of memory card for digital cameras. In order to store data, the compact flash utilises 'flash memory' and has a miniture IDE controller within the device.


It comes in two different types :-

• Type I - measuring 43mm x 36mm x 3.3mm

• Type II - measuring 43mm x 36mm x 5.5mm

 

The CF Type II slot is mainly used by 'Microdrives' and some other devices.

Both types are otherwise identical. CF I cards can be used in CF II slots, but CF II cards are too thick to fit in CF I slots. Flash memory cards are usually CF I.

 

CompactFlash is one of the oldest and most successful formats of memory cards, and has held on to a niche market with professional camera's. It has also 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 such as xD Picture Cards.

 

Flash memory, such as that in the compact flash format, supports only a limited number of erase/write cycles before a particular "sector" can no longer be written to. Memory specifications generally allow 10,000 to 1,000,000 write cycles. Typically the controller in a CompactFlash attempts to prevent premature wear of a sector by mapping the writes to various other sectors in the card - a process referred to as 'wear levelling'.

 

NOR-based flash has lower density than newer NAND-based systems, 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 at a later date. 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. The connector is about 43 mm wide, and the case is 36 mm deep and comes in two standard thicknesses, CF I (3.3 mm), and CF II (5 mm). Both types are otherwise identical. CF I cards can be used in CF II slots, but CF II cards are too thick to fit in CF I slots. Flash memory cards are usually CF I.

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, mobile 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. 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) . 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.