16Mb SD Card

Secure Digital, or SD, is a flash memory data storage device based on Toshiba's earlier Multi Media Cards (MMC). Measuring 32mm by 24mm by 2.1mm, SD is slightly thicker, and includes features that allow the secure exchange of data, enabling usage restrictions such as copyright protection.

As of October 2004, SD is the most popular flash memory format, having overtaken the older and larger Compact Flash[1] (http://www.theregister.co.uk/2004/01/06/victory_for_cprm_sd_cards/). SD cards are currently only slightly more expensive than Compact Flash, and have greater support in consumer-level devices. SD Memory Cards are usually faster than MMC cards due to their use of 4 data lines, as opposed to the two used by MMC, and are comparable to Compact Flash in terms of speed. SD cards also have a greater memory capacity than MMC cards, with capacities up to 2 GB currently available (as of December 2004). Note that SD cards reserve a certain amount of space for the copyright information, so an SD card of a given nominal size will normally have slightly less usable storage space than an equivalent MMC card.

Another amusing but pointless fact is that the "SD" logo was recycled - it was originally used for "Super-Density Optical Disk", which was the Toshiba / Matsushita entry in the DVD format wars. This is why the "D" looks so much like half of an optical disk...

PDA devices such as Pocket PCs and Palm-powered devices frequently feature SD slots. PalmOne, HP, Dell, Toshiba, and other PDA manufacturers have made SD a standard on all of their PDAs. Many of the Sharp Zaurus models also use the SD format. SD is fairly well supported in the digital camera industry as well, used in all Kodak cameras. Olympus also produced some cameras with SD capability, but abandoned it in favor of its own proprietary xD-Picture cards.

Some GPS receivers also use SD cards to allow extra maps to be available, for example Magellan's Meridion GPS receivers (http://www.magellangps.com/en/products/product.asp?PRODID=153). In the Meridion Color receiver, the SD card is placed inside the unit, that is, the compartment containing the batteries must be opened and the batteries removed before the SD card can be removed or inserted.

Access to the SD card standard is restricted to members of the Secure Digital Card Association, who must must pay licensing fees and sign a non-disclosure agreement that prohibits open source drivers. [2] (http://www.newsforge.com/article.pl?sid=01/12/20/2224254&mode=thread)

A smaller version of the SD card has been developed. The miniSD card measures 21.5mm by 20mm by 1.4mm and is backward-compatible with the SD card via an adapter. Currently available capacities (as of December 2004) range up to 512 MB.

Sandisk has announced (http://www.sandisk.com/pressrelease/20050106a.htm) that they will begin manufacturing SD cards with a USB connector built-in, eliminating the need for a card reader. The line of cards is scheduled for release in Q1 2005.

External links

• Secure Digital Association (http://www.sdcard.org/)