Secure Digital (SD) was a memory card format for use in portable devices, such as PDAs, digital cameras, and GPS navigation devices. The Secure Digital standard was introduced in 1999 by a group including Panasonic, Toshiba and SanDisk as an update of the MultiMediaCard (MMC) that among other features allowed for digital rights management (DRM). MMC cards can be used in SD slots but not vice versa.
The D in the logo for SD cards is in the form of an optical disk, and this is because the logo was designed during the time that Panasonic and Toshiba were working on the Super Density disc, a forerunner to DVD-Video. That logo was simply reused for the later SD card.
Secure Digital cards are thicker than MMC, have asymmetrical slots in the sides to prevent inserting it upside down, and the electrical contacts are recessed beneath the surface of the card, protecting them from contact with a user’s fingers. Most Secure Digital cards have a sliding tab that covers a notch in the card to make the card read-only.
Officially, Secure Digital cards only went up to 2 GB capacity, but some unofficial 4 GB cards were available. These may not work in all devices that support Secure Digital.
The Secure Digital High Capacity (SDHC) format, introduced in 2006 supports cards with capacities up to 32 GB. The Secure Digital eXtended Capacity (SDXC) format, introduced in 2009 supports cards up to 2 TB. SanDisk continued to list the original Secure Digital card in 2 GB form on its website until 2015.
Secure Digital cards are available in two additional smaller form factors, miniSD and microSD for use in devices such as mobile phones and tablet computers. Adapters allow the use of a smaller card in a slot built to hold a larger card.
The biggest risks for preservation are data rot due to loss of charge in drives unused for many years or physical damage to the card.
Figures
Dimensions: 32 mm × 24 mm × 2.1 mm
Capacity: 1 MB to 2 GB (some 4 GB cards were available that didn’t fully comply with Secure Digital standards)
Sources / Resources
- SanDisk SD and SDHC Cards [archived, 2015]
- Panasonic Lumix DMC-FZ8 Operating Instructions Manual p. 5 [mentions 4 GB SD cards]
- SD Association
- The Odd History of the SD Logo – YouTube
- MMC vs SD Card – Difference and Comparison
- Secure Digital – Wikipedia
Preservation / Migration
Media Stability Rating
Obsolescence Rating
