There are two main types of flash memory - NAND and NOR. NAND flash is the most suited for use in flash card applications because it has faster read and writes, is generally smaller, and is well suited to file type applications. NOR on the other hand is used for BIOS and EPROM type applications.
The Flash name is derived from the fact that changes to the data are made in "in a flash".
When the power is switched off, all data stored on the flash device is retained (non-volatile), unlike PC memory. Flash memory, basically acts like a solid-state hard disk. The flash memory requires no power to retain the data.
Flash chips are packaged into a casing making a flash card. Depending on the type of card the casing may or may not include a controller chip. In cases where a controller chip is not included, the controller chip will be mounted in the device that needs to access the card.
The main types of Flash Memory
PC Card (formerly PCMCIA Personal -Computer-Memory-Card-International-Association) (ATA cards)
These 68 pin cards were developed to a standard to be used in notebooks. Not only for memory, but also for modems, network cards etc. They are of a fixed size, but the thickness can vary.
Size (85.6mm x 54mm)
Type I - 3.3mm thick - e.g. Memory
Type II - 5.0mm thick - e.g. Modem
Type III - 10.5mm thick - e.g. Hard Disk
Flash Memory is usually built to the Type I or II standard. PC-Cards can have capacities up to 1GB, and are mostly used in high-end digital cameras.
SmartMedia (SSFDC Solid-State-Floppy-Disc-Card)
SmartMedia is very small and thin (37mm X 45mm X 0.76mm). And weighs only 2 grams. Due to its small size it is ideal for use with portable devices and is available with capacities up to 128MB. SmartMedia only contains the flash chips with no controller on board. The cards are mostly used in digital cameras and MP3 players.
CompactFlash cards (43mm x 36mm x 3.3mm) are thicker, but more rugged that SmartMedia cards. CompactFlash cards have 50 pins and have a controller on board and are available with capacities of up to 512MB. Since CompactFlash cards have an ATA interface they can easily be used in a PC-Card (PCMCIA) slot with the use of an inexpensive adapter.
The 7 pin MutiMedia cards ( 34mm x 32mm x 1.4mm,) are the newest type of card. There are two versions (ROM) Read-Only-Memory. These ROM cards are used to store information permanently, like an electronic version of the yellow pages that could be used with a mobile phone. The other version is a flash version for use in digital cameras etc. The multimedia card is available in capacities up to 128MB. Up to 30 cards can be joined on a single bus.
The 10 pin Memory Stick (24.5mm x 50mm x 2.8mm) is an innovation by Sony and is designed to be used in Sony and other types of notebooks, PDA’s and digital cameras etc. Capacities up to 64MB are available...