What is Secure Digital?

The Secure Digital (SD) Memory Card is a flash memory storage device designed by the consortium of Matsushita Electric (Panasonic), SanDisk and Toshiba to meet the security, capacity, performance and environmental requirements inherent in emerging audio and video consumer electronics devices.

The SD Card design is highly leveraged from the previous MultiMediaCard (or MMC) specification. Key enhancements over the MultiMediaCard include cryptographic security for protection of copyrighted data, a 4X improvement in maximum data transfer rate and a user-selectable write protect switch on the card casing. Improvements in Electro Static Discharge (ESD) tolerance are also provided through enhancements to the card’s protective casing.

Introduction of the SD card effectively replaced MMC cards because of their superior data transfer rates.  Products often accept both MMC and SD card standard however the SD card is the card type that should generally be used.

As with all flash memory, SD Memory Cards are non-volatile, which means they do not require power to retain the information stored on them. They are solid-state devices, so they have no moving parts to skip or break down. They will offer an incredible combination of high storage capacity (512MB in 2002), fast data transfer, great flexibility and excellent security. And of course, incredibly small size.

SD will facilitate fast, simple, secure downloading of all types of digital files, like music, movies, photos, news — even cooking instructions for your microwave. Once downloaded to your PC, you can organize and store the files as you wish. Then easily transfer the files from your PC to a super-compact SD Memory Card, which will be accepted by a whole variety of future SD-enabled products. Of course, you will also be able to directly record your own audio, video, still photos, and more onto SD Memory Cards, as such products become available.

Characteristics of Secure Digital (SD) Cards?

The SD Card is ideally suited for portable digital devices such as audio players, digital still cameras, digital video camcorders, handheld PCs and cell phones. The SD Card is 32 millimetres long, 24 mm wide and 2.1 mm thick. The card is slightly thicker than a MultiMediaCard allowing it to contain more memory for higher data capacity while maintaining the smallest area profile in the market.

Host systems designed for the SD Card will allow reading and writing of existing MultiMediaCards thus ensuring that existing user data can be easily migrated to, and used in, next generation systems.

What are the packaging and memory tolerances?

SD Card packaging includes a new high performance, nine-pin SD interface that enables data transfer rates of up to 10 megabytes per second. New proprietary interface commands facilitate the secure exchange of content between host devices, like PCs and music servers and the card itself.

The security level provided in the SD Memory Card has been designed to comply with both current and future SDMI (Secure Digital Music Initiative) portable device requirements. A mechanical write protect slide switch provides the consumer with added protection against accidental overwriting or erasure of data stored on the card.

The ESD (Electrostatic Discharge) tolerance has been significantly increased from that of MMC cards to ±10 Kvolts for contact discharge in the area of the interface pins and air discharge up-to ±15 Kvolts at all other points on the card body. A 9-pin serial interface ensures low cost integration into any device due to minimal pin count.

What SD storage capacities are available?

Storage capacities offered are 8, 16, 32, 64, 128, 256 and 512 Mbytes. Improvements in flash memory densities coupled with reductions in die size area will enable capacities of 2 Gbytes within the year 2003.

Does the brand of SD card matter?

Yes. As many Palm and other PDA users can attest to, there are quite significant differences in the speed performance of certain card brands.  The controller employed by SanDisk throughout 2002+ in their SD card is approximately half the speed on a Palm Tungsten PDA for data read/write that that of a Toshiba or Panasonic / Lexar SD card.  Their were also problems associated with compatibility with the Palm M series and SanDisk 128MB+ SD cards that can be attributed to the controller IC.

Differences in SD card brand may not be so important for digital cameras and other SD compatible devices.  Performance cards are generally considered to be Lexar and Toshiba makes due to their specific controller design.