Compact Flash card (CF) is a type of a data storage device, especially useful for portable electronic devices. It can be used directly in a CF card slot with an adapter. It makes use of flash memory. Based on physical features, there are two types of Flashcards: Type I (3.3mm thick) and the thicker Type II (CF2) cards (5mm thick).

First produced by SanDisk in 1994, Compact Flash card is among the first and the oldest and also the most successful brands and is now used for a variety of devices which includes laptops, portable audio recorders and desktop computers and cameras.

Flash memory devices consume very less power and yet have good transfer speeds. They can also be switched from one system to another. They are also designed to adjust to very rapid changes in temperature or in voltage. The storage capacity of a Compact Flash card ranges from 128 MB to about 64 GB. However, 256 MB and 2 GB are the most popular choices in Europe.

Flash memory has a specific quality which allows a section of its memory cells to get erased in a single 'flash', very much reminiscent of a camera flash function. This reminds one of the ease with which erasure of data can be carried out, freeing space for recording new data onto it. Flash memory being non-volatile and solid state, can be electrically erased and rewritten. Flash memory allows multiple memory locations to be erased or written in one programming operation. It can thus operate at much higher read-access speeds. Better shock resistance than hard disks is another of its useful feature. Features as these make these cards much more preferable over the others such as battery-powered devices.

A limitation of this card is that being easily rewritable memory, it can be overwritten without warning leading to loss of data. System failure, power fluctuations, corruption caused by hardware crash or software malfunctions are the other limitations.

Flash memory stores one bit of information in an array of transistors, called 'cells'. Compact Flash cards are built on the basis of the type of logic gate used in each storage cell and are thus of two types: NOR flash and NAND flash. Recently however, some flash memory devices called multi-level cell devices, can store more than one bit per cell. NOR flash cell has two gates: the Control Gate and the Floating Gate. NAND Flash has a different mechanism: tunnel injection for writing and tunnel release for erasing.

The market demand today is tilting towards the lower-priced NAND flash.