Computer Memory

Computer memory is usually meant to refer to the semiconductor technology that is used to store information in electronic devices. Current primary computer memory makes use of integrated circuits consisting of silicon-based transistors. There are two main types of memory: volatile and non-volatile.


Volatile memory is computer memory that requires power to maintain the stored information. Current semiconductor volatile memory technology is usually either static RAM (see SRAM) or dynamic RAM (see DRAM). Static RAM exhibits data remanence, but is still volatile, since all data is lost when memory is not powered. Whereas, dynamic RAM allows data to be leaked and disappear automatically without a refreshing. Upcoming volatile memory technologies that hope to replace or compete with SRAM and DRAM include Z-RAM, TTRAM and A-RAM.


Non-volatile memory is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory (see ROM), flash memory, most types of magnetic computer storage devices (e.g. hard disks, floppy discs and magnetic tape), optical discs, and early computer storage methods such as paper tape andpunched cards.Upcoming non-volatile memory technologies include FeRAM, CBRAM, PRAM, SONOS, RRAM, Racetrack memory, NRAM and Millipede.


Non-volatile memory is typically used for the task of secondary storage, or long-term persistent storage. The most widely used form of primary storagetoday is a volatile form of random access memory (RAM), meaning that when the computer is shut down, anything contained in RAM is lost. Unfortunately, most forms of non-volatile memory have limitations that make them unsuitable for use as primary storage. Typically, non-volatile memory either costs more or performs worse than volatile random access memory.


Non-volatile data storage can be categorized in electrically addressed systems (read-only memory) and mechanically addressed systems (hard disks,optical disc, magnetic tape, holographic memory and such). Electrically addressed systems are expensive, but fast, whereas mechanically addressed systems have a low price per bit, but are slow. Non-volatile memory may one day eliminate the need for comparatively slow forms of secondary storage systems, which include hard disks.

Computer memory types

Volatile

DRAM, e.g. DDR SDRAM SRAM Upcoming T-RAM Z-RAM TTRAM Historical Delay line memory Selectron tube Williams tube

Non-volatile

ROM PROM EPROM EEPROM Flash memory FeRAM MRAM PRAM Upcoming CBRAM SONOS RRAM Racetrack memory NRAM Millipede Historical Drum memory Magnetic core memory Plated wire memory Bubble memory Twistor memory

source: http://en.wikipedia.org/wiki/Computer_memory, http://en.wikipedia.org/wiki/Non-volatile_memory