There are primary storage and secondary storage devices that can be used with a computer based information system. The two main types of primary storage devices are RAM and ROM.
RAM (Random Access Memory) comes in different varieties. Including:


DRAM (Dynamic RAM).Cheapest and slowest. Uses a transistor to store a binary unit. Capacitor has to refresh its memory thousands of times a second. Commonly used for main system memory.

SRAM (Static RAM). Faster but more expensive than DRAM. Does not use capacitors so does not need constant refreshing like a DRAM. Commonly used in CPU cache memory.

EDO ( Extended Data-Out) DRAM. Better than standard DRAM because it has more than one memory location, speeding up data access. Also commonly used in main system memory.

SDRAM (Synchronous DRAM). Most common RAM in desktop computers. Uses higher speed to read data bits. Common in main system memory.

RDRAM (Rambus RAM). Uses high speed data bus (connecting link to CPU) to access high memory locations. Memory chips work together to achieve high data access speeds. But needs a specifically desgined motherboard. Common in main system memory.

VRAM (Video RAM). High speed. Used to hold graphics data and textures. Many different types of VRAM. Used in 3D accelerator graphics cards.


ROM. Permanent data storage. Data must be added during manufacture. Only costs a few cents each to mass produce. Rarely used in computers now, but found in toys and novelties like musical greeting cards and singing birthday candles.

PROM (Programmable ROM). Permanent data storage. ROM chips are manufactured blank and the data is added by the user, through a 'burning in' process. Once added the data cannot be changed. Easily damaged by static electric charges. Used in security systems that need to prevent any alteration of the data. Rarely now used in computers.

EPROM (Erasable Programmable ROM). Data can be erased. New data can then be added. Rarely used in modern computers, now replaced by EEPROM.

EEPROM (Electronically Erasable Programmable Data). Data can be easily altered without the need for special equipment to remove the chip. Used in cash registers, computer BIOS (Basic Input Output System), and most applications that need to store data without using power.