History of Computers - RAM

Page created by Brett Gutstein, 22 August 2011

Random Access Memory (RAM)

In general terms, RAM is a type of computer memory that can be accessed randomly, meaning that any unit of memory can be accessed without touching the preceding units. Today, RAM is the "working memory" storage area within the computer. Everything that is currently used and running is cached in RAM, allowing very fast access to that information from e.g. the CPU, since RAM is times faster than ordinary drives.

Overview

Prior to the creation of electronic RAM, devices such as the loom used programmable slots that could still be considered read only memory. The earliest form of electronic RAM is drum memory, which was invented in the 1930s. A drum formed the working memory of early machines, and programs were loaded on and off the drum with punched cards or paper tape. In the 1940s, magnetic core memory was invented. It uses the polarities of small magnetic ceramic rings to store information.

a stick of DRAM

Today, the most commonly used type of RAM is dynamic RAM (DRAM), which was first publicly released in 1970 with the Intel 1103 chip. Technically, DRAM is not random access because data is read in bursts, but the name has stuck. DRAM stores each bit of data in a separate capacitor/transistor pair called a memory cell within an integrated circuit. Each capacitor can be either charged or discharged, and these two states are taken to represent 1 and 0, the two values of a bit. The charged state represents a 1, and the discharged state represents a 0. However, the capacitors in DRAM leak charge. In only a few milliseconds, a fully charged capacitor will become completely discharged unless it is refilled by the CPU or memory controller. Capacitors are like "leaky buckets" being refilled, and the refilling operation happens automatically thousands of times per second. (This refilling operation is how DRAM got its name, the capacitors have to be dynamically refilled or they do not work correctly). Dynamic memory refresh controllers utilize a type of transitor transistor logic called refresh logic to determine which capacitors need to be refilled. Transistors in DRAM allow the control circuitry on the memory chip to read the capacitor or change its state. Also, DRAM is volatile, meaning that it loses its contents when its power is cut.

Significance

RAM is significant in the history of computers because it enabled the creation of machines that had memory (RAM was invented before the HDD). Also, in today's computing world, RAM is necessary for all computers to function. Without RAM, computers would run at excruciatingly slow speeds. Random reads from memory are over 100,000 times faster than random reads from a hard drive, so if computers had to execute all programs and obtain all data directly from their hard drives they would be effectively unusable.

Links

http://en.wikipedia.org/wiki/RAM

http://www.howstuffworks.com/ram.htm

http://www.wisegeek.com/what-is-random-access-memory.htm