More and more these days, users of portable electronic devices are storing data on portable memory sources. 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.

A microSD card is one of the smallest flash memory cards on the market today. 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. Finally came the microSD card, the smallest of them all.

As its name suggests, a microSD card is tiny. Most technical measurements for the microSD card put it at 15x11x1. That's millimeters, of course, and the card is roughly the size of a fingernail. In the race to store more information in less space, the microSD card is at the head of the class.

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 microSD card slots. When used in a mobile phone or portable GPS device, the microSD card is typically embedded in the electronic device. Some mobile phones or GPS trackers have removable microSD 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 and microSD 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 microSD card holds, the more expensive it will be.

This increase in capacity does not mean a corresponding increase in physical size, however. The wonders of modern technology that keep computer hard disk drives smaller and smaller while able to hold more and more data apply to a microSD card as well. The 128 MB microSD card looks very much like the 2 GB microSD card. You'll notice the difference when you swap out one for the other in a digital audio player: suddenly, you can store a lot more songs.