Memories made out of semiconductor elements which are generally integrated into computers as the main memory and used to prepare large volumes of data and programs.
A distinction is made between:
ROM:
Read-only memory. Memory content can be neither modified nor erased. Non-volatile type of memory. Programming via masks during fabrication.
RAM:
Random-access memory; volatile type of memory. Programming and erasure are performed electrically.
PROM:
Programmable read-only memory. Programming is performed electrically, erasure is not possible. Non-volatile type of memory.
Erasable programmable read-only memory; programming is performed electrically, erasure via UV light radiation. Non-volatile type of memory.
Electrically erasable programmable read-only memory; programming is performed electrically; non-volatile type of memory.
EAROM:
Electrically alterable read-only memory; programming is performed electrically, electrical erasure is also possible a word at a time. Non-volatile type of memory. Highly suitable for machine controls.
Dynamic RAM, DRAM:
The information appears as an electrical charge, which then leaks away again. To prevent it being lost, the charge is renewed at short intervals (of a few ms). This occurs automatically via the processor.
DRAM is currently available up to 1 Mbit.
Static RAM, SRAM:
The storage cells consist of bistable circuitry elements with a functionality similar to that of a flip-flop. The information is not volatile; it is stored until the storage element concerned is rewritten. SRAMs are significantly more expensive than DRAMs.