The CompactFlash card (also known as CF Card), was originally a popular storage device for digital cameras. In the past few years, it has been replaced by smaller cards on the consumer end, but it is still a preferred format for DSLR cameras, because of its superior capacity and reliability.
The Compact Flash speed rating refers to the speed the camera or data is written to the card. Most CompactFlash cards are speed rated and come in standard speeds such as 40x, 80x, and 133x. The X represents the transfer rate, and 133x for example means the card can perform data transfer at 133 × 150 KiloBytes (KB) per second, which is approximately 20 MB/s.
High-Speed CF cards are a brilliant investment for any photographer. Besides enhancing in-camera functions and greatly reducing photo transfer time, you get the added enhancements of security and memory features that make selecting a high-speed memory card an easy choice. If you're not using a speed-rated memory card, now's the time to make the switch!
There are two main types of CF cards, Type I (3.3 mm thick) and the thicker Type II (CF2) cards (5 mm thick).
CompactFlash cards are currently available in various capacities up to 512GB.