The Compact Flash, often abbreviated to "CF", memory card format was originally introduced by SanDisk in 1994. It was originally available in two different types, "Type I" and "Type II", both of which measured 43mm x 36mm in surface area, but differed in thickness, 3.3mm and 5.0mm respectively, reflecting the different widths of PC slot available at the time. Type II Compact Flash cards are now largely obsolete. Compact Flash cards contain memory chips and a controller, and were the first type of memory expansion card to effectively become "standard" in the digital camera market, offering storage capacities of between 8MB and 8GB.
Compact Flash cards, as the name suggests, employs non-volatile, "flash" memory, the data contained in the memory remains, even if power is disconnected, until transferred elsewhere, or deleted, by the user, and are therefore suitable for a wide range of digital storage applications, including in digital cameras and camcorders, PDA ("Personal Digital Assistant") devices, MP3 players, etc.
Data transfer speeds to, and from, a memory expansion card, the "write" speed, or the rate at which data can be written to the card, in particular, are of paramount importance to a digital photographer who wants to take multiple photographs in rapid succession. Too slow a write speed may mean that a digital camera is still processing the data from a previous photograph when the photographer himself, or herself, is ready to take the next shot, and the moment may be lost. The fastest Compact Flash cards, however, offer a combined read/write speed of 40MB per second, or 266 times faster than a single speed CD-ROM, and Compact Flash remains a popular for digital compact, and digital SLR ("Single Lens Reflex"), cameras.
In terms of storage capacity, while the sky is not quite the limit, Compact Flash memory cards are typically available in storage capacities between 512MB and 8GB, and 16GB, 32GB, 48GB and even 64GB models are becoming increasingly available. Do bear in mind, however, that these very high capacity Compact Flash cards are not, necessarily, the fastest, and, if you are using a FAT ("File Allocation Table") based device, the host device does need to support the FAT32 file system, for Compact Flash cards of over 2GB storage capacity. As a rule of thumb, you can calculate the total number of digital photographs, for example, that can be stored on a Compact Flash card by calculating the storage space required for a single photograph, and dividing the total storage space available. A typical compact digital camera, with a maximum resolution of 3.3Mp has an effective image size of 3.1Mp, and therefore, allowing for RGB ("Red, Green, Blue") colour components, requires 9.3MB of storage space; a 512MB Compact Flash card could therefore hold 55 such digital photographs, whereas a 16GB card could hold 1,720.
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