People who use portable electronic devices often want to store their data in a way that is portable. This is true especially for users of mobile phones, portable global positioning system (GPS) devices, and video and audio players and recorders. One of the primary formats for these portable memory sources is a microSD card, which is one of the smallest flash memory cards on the market. It is manufactured by SanDisk, which lends the SD to the name; the other part of the name comes from the tiny size of the card.
SanDisk originally manufactured the SD card, which was a bit larger than the microSD card. Then came the miniSD card, which was a bit smaller, and the microSD card, the smallest of them all. Most technical measurements for the tiny card put it at 15 by 11 by 1 mm (roughly 0.59 by 0.43 by 0.04 inches), which is roughly the size of a fingernail.
The microSD card is about a quarter of the size of a standard SD card, but it can still be used with devices that have SD card slots by using a special adapter. Portable audio and video players feature SD card slots, and some of the latest models even have the smaller slots. When used in a mobile phone or portable GPS device, the card is typically embedded in the electronic device. Some mobile phones or GPS trackers have removable cards, but that feature is usually reserved for devices of a different nature, namely those that lend themselves to expandable and collapsible memory needs, like video and audio players.
The general idea behind SD cards is that they can have memory capability of varying quantities. A common amount of memory for one of these cards is 1 gigabyte (GB), although microSD cards are also available in capacities of 128 megabytes (MB), 256 MB, 512 MB, and 2 GB. The more data the card holds, the more expensive it will be.
This increase in capacity does not mean a corresponding increase in physical size, however. The technology that allows computer hard disk drives to get smaller and smaller while being able to hold more and more data apply to a these memory card as well. The 128 MB microSD card looks very much like the 2 GB card, for example, but a user will notice the difference when he swaps out one for the other in a digital audio player.