Memory Cards for Digital Cameras - SD Cards

The MultiMediaCard (MMC) is an early flash memory card standard released by Siemens AG and SanDisk in 1997. Based on the MMC standard, the Secure Digital (SD) Cards were developed.

The main difference between SD and MMC is the write-protect switch in SD memory cards that give them the name of ‘secure’. Although the security feature did not turn out to be as important as expected, the SD memory card has almost superseded the original MMC.

Although not all SD variants are asymmetrical, most SD memory cards for digital cameras are easily recognisable from their asymmetrical design. Variants of the SD memory cards include mini SD, micro SD, SDHC (High Capacity) and SDXC (Extended Capacity). Mini SD (21.5 mm x 20.0 mm) and micro SD (11.0 mm x 15.0 mm) are among the smallest available memory cards available.

Capacity

SD memory card uses flash memory format and capacity of the SD memory card varies greatly depending on the variant of SD memory card. Older SD memory cards for digital cameras range from 512 MB of space to the more recent 4 GB. Even newer variants like SDHC is able to store up to 32 GB of space and the SDXC boasts of 1 TG of memory, nearly 250 times more than the standard SD memory cards today.

Transfer Speed

Guidelines from the Secure Digital Association specify that all SD memory cards have a Speed Class Rating based on their minimum write speed. These class ratings are divided into class 2, 4, or 6; class 2 is equivalent to 2 MB/s, class 4 is equivalent to 4 MB/s and so on. Other than the class ratings, SD memory cards are often advertised with their maximum speed. This speed is usually expressed in the ‘x’ rating where 1x is 150 kB/s and 10x is 1500 kB/s. In general, the transfer speeds of SD memory cards are highly than other memory cards of its range, such as CompactFlash. The prevalence and improvement of video recording capabilities in point-and-shoot digital cameras has made higher write speeds important to the average consumer, contributing to the popularity of SD memory cards.

Compatibility

Like other memory cards, standard SD memory cards for digital cameras use the FAT12 or FAT16 file system. SD memory cards with greater than 4 GB and the other variants like SDHC or SDXC memory cards uses a FAT 32 file systems and are not compatible with older SD card readers. Most digital cameras today are able to recognise the larger file system. Unless you are using an old digital camera, or a camera that does not accept SD memory cards, most digital cameras are compatible with SD memory cards.

Already, SD memory cards for digital cameras are the most common type of flash memory found in point-and-shoot digital cameras. With the extreme memory capabilities of the SDHC and SDXC memory cards today, it is very likely that more DSLRs will also incorporate SD memory card compatibility to take advantage of the large memory space.