SD Memory Guide

Secure Digital is a popular flash memory card developed by Matsushita, SanDisk, and Toshiba for the use in portable devices. It is widely used in digital cameras, PDAs, mobile phones, GPS devices, and video game consoles. The standard size SD card comes in capacities ranging from 8 MB to 4 GB, while the SDHC (Secure Digital High Capacity) comes in capacities ranging from 4 GB to 32 GB. A full sized SD card measures 24mm x 32mm x 2.1mm, they are based on the older MMC (MultiMediaCard) format. Devices with SD slots can also be used with MMC cards, however since the SD card is thicker it cannot be inserted in to an MMC slot.

The secure digital format was first developed to compete with Sony's Memory Stick format. Panasonic, SanDisk, and Toshiba began development in 1999. The SD card first became available in the beginning of 2000. SD card have a number of main differences from the MMC cards which they were based on. SD cards are shaped asymmetrically to insure they are not inserted upside down, while an MMC card could be inserted but not make contact. SD cards are physically thicker, SD cards typically have transfer rates in the range of 10-20 Mbps, however this is constantly improving with todays changing standards.

Some SD cards include a USB device for compatibility with laptop and desktop computers. It allows the Secure Digital card to be connected to any computer with a USB drive. SD cards offer an optional write-protect tab. It is a simple slidable tab or switch located on the left side of the card. When the write-protect tab is in the down position (Away from the end that is inserted, the card is write protected meaning it is read only. The write tab feature is considered optional by Secure Digital Association Guidelines. Some manufacturers believe that the write-protect switch is easily broken. If the sensor of the device is not functioning properly and unable to detect the notch, all SD cards will seem to be either write-protected or write-enabled.