Tuesday, September 30, 2008

Random Access Memory

Random-access memory (usually known by its acronym, RAM) is a type of computer data storage. Today it takes the form of integrated circuits that allow the stored data to be accessed in any order, i.e. at random. The word random thus refers to the fact that any piece of data can be returned in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.

This contrasts with storage mechanisms such as tapes, magnetic discs and optical discs, which rely on the physical movement of the recording medium or a reading head. In these devices, the movement takes longer than the data transfer, and the retrieval time varies depending on the physical location of the next item.

The word RAM is mostly associated with volatile types of memory (such as DRAM memory modules), where the information is lost after the power is switched off. However, many other types of memory are RAM as well (i.e. Random Access Memory), including most types of ROM and a kind of flash memory called NOR-Flash.

Types of RAM

  • FPM RAM, which stands for Fast Page Mode RAM is a type of Dynamic RAM (DRAM). The term Fast Page Mode comes from the capability of memory being able to access data that is on the same page and can be done with less latency. Most 486 and Pentium based systems from 1995 and earlier use FPM Memory.

  • EDO RAM, which stands for Extended Data Out RAM came out in 1995 as a new type of memory available for Pentium based systems. EDO is a modified form of FPM RAM which is commonly referred to as Hyper Page Mode. Extended Data Out refers to fact that the data output drivers on the memory module are not switched off when the memory controller removes the column address to begin the next cycle, unlike FPM RAM. Most early Penitum based systems use EDO.

  • SDRAM, which is short for Synchronous DRAM is a type of DRAM that runs in synchronization with the memory bus. Beginning in 1996 most Intel based chipsets began to support SDRAM which made it a popular choice for new systems in 2001.
    SDRAM is capable of running at 133MHz which is about three times faster than FPM RAM and twice as fast as EDO RAM. Most Pentium or Celeron systems purchased in 1999 have SDRAM.

  • DDR RAM, which stands for Double Data Rate RAM is a type of SDRAM and appeared first on the market around 2001 but didn’t catch on until about 2001 when the mainstream motherboards started supporting it. The difference between SDRAM and DDR RAM is that instead of doubling the clock rate it transfers data twice per clock cycle which effectively doubles the data rate. DDRRAM has become mainstream in the graphics card market and has become the memory standard.

  • DDR2 RAM, which stands for Double Data Rate 2 RAM is a newer version of DDR which is twice as fast as the original DDR RAM. DDR2RAM came out in mid 2003 and the first chipsets that supported DDR2 came out in mid 2004. DDR2 still is double data rate just like the original DDR however DDR2-RAM has modified signaling which enables higher speeds to be achieved with more immunity to signal noise and cross-talk between signals.

  • RAMBUS (RIMM) RAM is a type of ram of its own, it came out in 1999 and was developed from traditional DRAM but its architecture is totally new. The RAMBUS design gives smarter access to the ram meaning that units can prefetch data and free some CPU work. The idea behind RAMBUS RAM is to get small packets of data from the RAM, but at very high clock speeds. For example, SD RAM can get 64bit of information at 100MHz where RAMBUS RAM would get 16bits of data at 800MHz. RIMM ram was generally unsuccessful as Intel had a lot of problems with the RAM timing or signal noise. RD RAM did make an appearance in the Sony Playstation 2 and the Nintendo 64 game consoles.

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