Upgrading And Repairing PCs 21st Edition: Flash Storage

CompactFlash, SmartMedia, And MultiMediaCard


CompactFlash was developed by SanDisk Corporation in 1994 and uses the ATA (AT Attachment) architecture to emulate a disk drive; a CompactFlash device attached to a computer has a disk drive letter just like your other drives. When CompactFlash was first being standardized, even full-sized hard disks were rarely larger than 4 GB, so the limitations of the ATA standard were considered acceptable. However, CF cards manufactured after the original Revision 1.0 specification are available in capacities up to 128 GiB. While the current revision 6.0 works in [P]ATA mode, future revisions are expected to implement SATA mode.

The original size was Type I (3.3 mm-thick); a newer Type II size (5 mm-thick) accommodates higher-capacity devices. Both CompactFlash cards are 1.433-inch wide by 1.685-inch long, and adapters allow them to be inserted into laptop computer PC Card slots. The CompactFlash Association oversees development of the standard.


Ironically, SmartMedia (originally known as SSFDC for solid state floppy disk card) is the simplest of any flash memory device; SmartMedia cards contain only flash memory on a card without control circuits. This simplicity means that compatibility with different generations of SmartMedia cards can require manufacturer upgrades of SmartMedia-using devices. Now defunct, the Solid State Floppy Disk Forum originally oversaw development of the SmartMedia standard.


The MultiMediaCard (MMC) was codeveloped by SanDisk and Infineon Technologies AG (formerly Siemens AG) in November 1997 for use with smart phones, MP3 players, digital cameras, and camcorders. The MMC uses a simple 7-pin serial interface to devices and contains low-voltage flash memory. The MultiMediaCard Association was founded in 1998 to promote the MMC standard and aid development of new products. In November 2002, MMCA announced the development of the Reduced Size MultiMediaCard (RS-MMC), which reduces the size of the standard MMC by about 40% and can be adapted for use with standard MMC devices. The first flash memory cards in this form factor were introduced in early 2004 to support compact smartphones. In 2008, the MMCA merged with JEDEC, which is the global leader in developing open standards for the microelectronics industry.


A SecureDigital (SD) storage device is about the same size as an MMC (many devices can use both types of flash memory), but it’s a more sophisticated product. SD, which was codeveloped by Toshiba, Matsushita Electric (Panasonic), and SanDisk in 1999, gets its name from two special features. The first is encrypted storage of data for additional security, meeting current and future Secure Digital Music Initiative (SDMI) standards for portable devices. The second is a mechanical write-protection switch. The SD slot can also be used for adding memory to Palm PDAs. The SDIO standard was created in January 2002 to enable SD slots to be used for small digital cameras and other types of expansion with various brands of PDAs and other devices. The SD Card Association was established in 2000 to promote the SD standard and aid the development of new products. Note that some laptop computers have built-in SD slots.

Reduced-size versions of SD include MiniSD (introduced in 2003) and MicroSD (introduced in 2005). MiniSD and MicroSD are popular choices for smartphones and can be adapted to a standard SD slot. MicroSD is compatible with the TransFlash standard for mobile phones.

The original SD standard allowed for memory card capacities of up to 2 GB. To support higher capacities the SDHC (High Capacity) standard was created in 2006. SDHC supports cards from 4 GB to 32 GB in capacity. To increase capacity beyond 32GB, the SDXC (eXtended Capacity) format was released in 2009. SDXC supports capacities of up to 2 TB. Note that devices are backward compatible, meaning that a device that supports SDXC also supports SDHC and standard SD cards. A device that supports SDHC also accepts standard SD cards, but such a device does not support SDXC cards. Devices that support only standard SD do not support either SDHC or SDXC cards.

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