Index: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Home > Random Access Memory

Random Access Memory or RAM is a type of computer storage whose contents can be accessed in any order. This is in contrast to sequential memory devices such as magnetic tapes, discs and drums, in which the mechanical movement of the storage medium forces the computer to access data in a fixed order. It is usually implied that RAM can be both written to and read from, in contrast to Read-Only Memory or ROM. RAM is usually used for primary storage in computers to hold actively-used and actively-changing information, although some devices use certain types of RAM to provide long term secondary storage.

1 Overview

Computers use RAM to hold the program code and data during execution. One defining characteristic of RAM is that its accesses to different memory locations are almost always completed at about the same speed, in contrast to some other technologies that required a certain delay time for a bit or byte to “come around”.

Early vacuum tube-based systems behaved much like modern RAM, even though the devices failed much more regularly. Core memory, which used wires attached to small ferrite electromagnetic cores, also had roughly equal access time (the term “core” is still used by some programmers to describe the RAM at the heart of a computer). The basic ideas behind tube and core memory are still used in modern RAM implemented with integrated circuits.

Alternative primary storage mechanisms usually involved a non-uniform delay for memory access. Delay line memory used a sequence of sound wave pulses in mercuryMercury also called quicksilver is a chemical element in the periodic table that has the symbol Hg ( L. hydrargyrum and atomic number 80. A heavy, silvery, transition metal, mercury is one of only two elements that are liquid at room temperature (the othe-filled tubes to hold a series of bits. Drum memoryDrum memory was an early form of computer memory that was widely used in the 1950s and into the 1960s. For many machines, a drum formed the main working memory of the machine, with data and programs being loaded on to or off of the drum using media such a acted much like the modern hard diskA hard disk (or hard disc or hard drive ) is a computer storage device. Mechanics A hard disk uses rigid rotating platters. It stores and retrieves digital data from a planar magnetic surface. Information is written to the disk by transmitting an electrom, storing data magneticallyIn physics, magnetism is a phenomenon by which materials exert an attractive or repulsive force on other materials. Some well known materials that exhibit easily detectable magnetic properties are iron, some steels, and the mineral lodestone; however, all in continuous circular bands. (See primary storage for a greater discussion of these alternatives and others.)

Many types of RAM are volatile, which means that unlike some other forms of computer storage such as disk storageDisk storage is a group of data storage mechanisms for computers; data is transferred to planar surfaces or disks for temporary or permanent storage. In the early 1960s single data bits were stored as magnetic charges in magnetic core memory. The scientis and tape storage, they lose their data when the computer is powered down. Modern RAM generally stores a bit of data as either a chargeCharge is a word with many different meanings. Science In science, the concept of charge is derived from the observation of conserved quantum numbers. Various charge-like quantum numbers have been introduced by theories of particle physics, e. electric ch in a capacitor, as in dynamic RAM, or the state of a flip-flop, as in static RAM.

Currently, there are several types of non-volatile RAM under development, which will preserve data while powered down. Technologies that are being used include carbon nanotube technology and magnetic tunnel effect.

In the summer of 2003, a 128 Kibit Magnetic RAM chip was introduced, which was manufactured with 0.18 micrometre technology. The core technology of MRAM is based on the magnetic tunnel effect. In June of 2004, Infineon unveiled a 16-Mibit prototype based on 0.18 µm technology once again.

As for carbon nanotube memory, a high-tech startup Nantero has built a functioning prototype 10 Gi b array in 2004.

An interesting use of RAM is allocating parts of it as a partition, effectively acting as a hard drive, only much faster. It is usually referred to as a ramdisk.

SRAM or Static RAM
NV-RAM or Non-Volatile RAM
DRAM or Dynamic RAM
- Fast Page Mode DRAM
- EDO RAM or Extended Data Out DRAM
- SDRAM or Synchronous DRAM
  - DDR SDRAM or Double Data Rate Synchronous DRAM
  - RDRAM or Rambus DRAM

3 Not-so-common types of RAM

Dual-ported RAM
Video RAM, a dual-port memory with one random access port and one sequential access port. This is becoming more popular as people need more and more video memory. See description under Dynamic random access memory.
WRAM
MRAM
FeRAM

4 RAM packaging

Semiconductor RAM is produced as integrated circuits (ICs). RAM ICs are often assembled into plug-in modules. Some standard module types are:

Single in-line Pin Package ( SIPP )
Dual in-line Pin Package ( DIPP )
Single in-line memory module ( SIMM)
Dual in-line memory module ( DIMM)
Rambus modules are actually DIMMs, but are often referred to (by Rambus themselves and others) as RIMMs due to their proprietary slot.

Digital electronics Computer memory

<Hide>

Topics: Random Access Memory, Overview, Common Types Of RAM...

Random accessIn computer science, random access is the ability to access a random element of a group in equal time. The opposite is sequential access, where a remote element takes longer time to access. A typical illustration of this distinction is the ancient scroll	Random variableA random variable can be thought of as the numeric result of operating a non-deterministic mechanism or performing a non-deterministic experiment to generate a random result. For example, rolling a dice and recording the outcome yields a random variable w	Random Access MemoryRandom Access Memory or RAM is a type of computer storage whose contents can be accessed in any order. This is in contrast to sequential memory devices such as magnetic tapes, discs and drums, in which the mechanical movement of the storage medium forces
RandomizerIn telecommunication, the term randomizer has the following meanings: 1. A device used to invert the sense of pseudorandomly selected bits of a bit stream to avoid long sequences of bits of the same sense. Note: The same selection pattern must be used on	Random numberIn statistics a random number is a single observation (outcome) of a specified random variable. Where no distribution is specified, the continuous uniform distribution on the interval [0,1) is usually, but not always, intended. In an informal sense, there	RandomnessIn ordinary language, the word random is used to express apparent lack of purpose or cause. This suggests that no matter what the cause of something, its nature is not only unknown but the consequences of its operation are also unknown. In most technical
Random sequence	Randomization	Random Harvest
Random Lake, Wisconsin	Random optimization	Randomized controlled trial
Random House	Random walk	Random walk Monte Carlo

Non User