veloped by Matsushita, SanDisk and Toshiba for use in portable devices, including digital cameras, handheld computers, PDAs and GPS units. As of 2006, SD card capacities include 8MB, 16MB, 32MB, 64MB, 128MB, 256MB, and 512MB, 1GB, 2 GB, 4 GB, 6 GB, 8 GB (4-32 GB: SDHC)[1] and 32GB.The format has proven to be very popular. However, compatibility issues between older devices and the newer 2 GB and larger cards and the SDHC format have caused considerable confusion for consumers.
Form factor
SD cards are based on the older MultiMediaCard (MMC) format, but have a number of differences:
- The SD card is asymmetrically shaped so that it cannot be inserted upside down, whereas an MMC will go in most of the way but not make contact if inverted.
- Most SD cards are physically thicker than MMCs. SD cards generally measure 32 mm × 24 mm × 2.1 mm, but can be as thin as 1.4 mm, just like MMCs (see below).
The contacts are recessed beneath the surface of the card (like Memory Stick cards), protecting the contacts from contact with the fingers
- SD cards typically have higher data transfer rates, but this is always changing, particularly in light of recent improvements to the MMC standard.
- Digital rights management features are available but are seldom used.
Devices with SD slots can use the thinner MMCs, but the standard SD cards will not fit into the thinner MMC slots. SD cards can be used in CompactFlash or PC card slots with an adapter. miniSD and microSD cards can be used directly in SD slots with a physical interface adapter. There are some SD cards with a USB connector for dual-purpose use, and there are card readers which allow SD cards to be accessed via many connectivity ports such as USB, FireWire, and the common parallel port. SD cards can also be accessed via a floppy disk drive with a FlashPath adapter.
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