Flash memory is an example of quite a recent type of storage technology known as solid state devices. This type of portable storage has become very popular because of its low price and high storage capacity compared to its rivals, e.g. floppy disk.
Solid state devices are regarded as being robust and reliable because they have no moving parts with the data stored in semiconductor chips. This technology already exists in the form of flash memory used to store the Basic Input/Output System (BIOS) of a motherboard.
Unlike ROM, flash memory can be read form and written to and unlike RAM does not require power to retain its data.
Although these devices typically cannot hold as much data as hard disks, CD-ROMs and DVDs, the storage capacity is continually increasing.