SD Secure Digital Memory Cards & SDHC Memory Cards

SD or Secure Digital memory cards are a digital media format that are universally compatible with many of the latest digital devices including digital cameras, digital camcorders, mobile phones, MP3 players and PDA's.

The standard Secure Digital card measures 24mm x 32mm x 2.1mm. SD cards are by far the most universally used memory card format in today’s marketplace but due to the 2GB capacity limit SDHC memory cards that are available up to 32GB are becoming more popular. The standard SD card has a 2GB limit.

The SD card allows users to store any type of Digital media such as photo, music and video and move it between cameras, PC's and any other supported device. SD cards are now available in different speed formats, these are measured in MB/s. There are two different speeds measured on SD cards - the read speed and the write speed. The read speed is the speed at which the Secure Digital memory card can be read by either the camera or PC and the write speed is the speed at which data is written onto the card. This is usually noticable in how much time the user has to wait between shots.

Most devices can use SD cards up to 2GB in capacity. But alot of new cameras can now use a new format of SD card. This is called the SDHC card (SD High Capacity).

SDHC memory cards are only compatible with devices which show the SDHC logo. This  format starts at 4GB and is currently available up to 32GB. SDHC card speeds are also measured in a different speed format. These are Class 2, Class 4 and Class 6. The 2,4 and 6 stand for 2MB/s, 4MB/s and 6MB/s read/write speed. These denote the minimum sustained read/write speed requirements. A Class 4 SDHC memory card must have a minimum read and write speed of 4mb/s. Class 6 is currently the fastest speed with many class 6 memory cards having a faster read/write speed than 6mb/s especially the Sandisk Ultra and Extreme ranges.

In late 2010 another format with the same dimensions as SD and SDHC will be released. This format is called SDXC and has the capabilities in the future to be produced up to a whopping 2TB. This new format is being produced due to the limitations of SDHC (technology has a 32GB limit). The need for SDXC cards has arisen due to the high memory needs of HD video recording devices which use roughly twice as much memory as standard video recording devices.