Compact Flash Cards, Memory and Readers

Compact Flash (CF) memory card is a popular removable storage media used mainly in digital cameras and similar portable devices. It is available in many forms, sizes, speeds, capacities and price ranges. CompactFlash cards are manufactured by SanDisk, Samsung, Sony, Kingston Technology, Kodak, Panasonic, Toshiba, Canon and many other manufacturers. The main media that is used to store the data is Flash memory but there are also CompactFlash memory cards that use a small 1" hard drive for storage. Another property that connects Compact Flash cards and hard drives is the interface.

Compact Flash uses interface which is electrically compatible with IDE/ATA standard. This makes it very easy to connect any Compact Flash with a suitable adapter to a standard hard drive IDE/ATA connector on the PC motherboard. Because of this compatibility Compact Flash Cards are used also in many embedded systems instead of hard drives. There are two main types of Compact Flash cards. Compact Flash Type 1 (CF) is 3.3 mm thick, while Compact Flash Type 2 (CFII) is 5 mm thick. Electrical interface is the same for both types. Compact Flash card Type 2 is also used for Microdrives – Compact Flash cards with a real 1" hard drive.

To access Compact Flash cards with personal computer we need a memory card reader. This is a small device with slots for popular memory cards (CF, CFII, SD, Memory Stick, xD, etc.) and USB/FireWire interface. Memory card is visible under operating system as a disk—it can be formatted and used as ordinary hard drive. Therefore memory cards need no special device driver. Another possibility is to use CF/IDE adapter to connect CF memory card as a hard drive. There are also CF/SATA interfaces to use CF cards where ATA connection is not available. Theoretically it is also possible to install a complete operating system to a Compact Flash (CF) card and boot from there but this requires special preparation and settings since most operating systems create large swap files and heavily use the system disk.

Flash Memory

CompactFlash cards use NAND flash memory (except Microdives which are tiny hard drives). Flash memory is durable but has limitations. Typical cards have endurance of 1 000 000 writes to a specific location. Compact Flash cards also include error correction checking algorithms that detect and correct errors during reading. But if the same locations would be constantly used to write data they would wear out before other rarely used locations. To solve this problem cards also use wear leveling protection mechanisms to equally distribute writing across all memory address space. Each card has a controller which acts as a bridge between IDE/ATA interface and memory chips. This controller is also responsible for bad cell management, error correction and wear leveling. The flash memory controller during card initialization maps out bad memory cells and takes care for mapping file system sectors to memory locations. If a card is inaccessible it is mainly due to a failed controller.

File System

CompactFlash cards mainly use FAT file system. FAT12 was used for smaller cards, FAT16 can be used up to 2 GB and FAT32 can be used for larger capacities. You can also format it with NTFS but many portable devices do not support this file system. Data recovery is possible regardless of file system used.

Data Recovery

Compact Flash memory card format is popular storage media for a wide variety of devices. Therefore failed memory cards are not rare. Data from inaccessible Compact Flash cards can be recovered using standard flash memory reading procedures. This usually means removing memory chips and reading them in a special flash memory reader. This is not easy and requires special equipment. In such cases when the card is electrically or physically damaged it is best to leave data rescue operation to professional data recovery companies.

In some cases the card will continue to work but the data will be corrupted and files lost. It this case you can try standard digital image recovery or universal data recovery software to recover corrupted file system and erased files. However, there are two ways how your computer connects to CompactFlash card. A typical connection is via USB memory card reader. Unfortunately, this kind of connection does not allow direct access to the card via ATA commands. Therefore it is better to connect the card directly via appropriate CF card to IDE/ATA adapter. This will allow the recovery software to communicate directly with the card at the lowest level. But you should be careful. CF cards have no write protection—always make a copy of the card data before doing any data recovery.

Compact Flash cards are considered more durable and rugged comparing to other similar cards. But one aspect is mechanical durability–all memory cards are still sensitive electronic devices.

Compact Flash cards offer not only high capacity but also high speed access and are common storage media used in professional digital cameras. To avoid lost files and expensive digital image recovery it is advisable to make a daily backup of all the files on the card to a laptop computer or any other appropriate place.

Tags: , , , , ,