Random-Access Memory


Computer Engineering; Information Technology


Random-access memory (RAM) is a form of memory that allows the computer to retain and quickly access program and operating system data. RAM hardware consists of an integrated circuit chip containing numerous transistors. Most RAM is dynamic, meaning it needs to be refreshed regularly, and volatile, meaning that data is not retained if the RAM loses power. However, some RAM is static or nonvolatile.



The speed and efficiency of computer processes are among the most areas of greatest concern for computer users. Computers that run slowly (lag) or stop working altogether (hang or freeze) when one or more programs are initiated are frustrating to use. Lagging or freezing is often due to insufficient computer memory, typically random-access memory (RAM). RAM is an essential computer component that takes the form of small chips. It enables computers to work faster by providing a temporary space in which to store and process data. Without RAM, this data would need to be retrieved from direct-access storage or read-only memory (ROM), which would take much longer.

Computer memory has taken different forms over the decades. Early memory technology was based on vacuum tubes and magnetic drums. Between the 1950s and the mid- 1970s, a form of memory called “magnetic-core memory” was most common. Although RAM chips were first developed during the same period, they were initially unable to replace core memory because they did not yet have enough memory capacity.

There are two major categories of random-access memory: static RAM (SRAM) and dynamic RAM (DRAM). Static RAM may be asynchronous SRAM (ASRAM) or synchronous.

There are two major categories of random-access memory: static RAM (SRAM) and dynamic RAM (DRAM). Static RAM may be asynchronous SRAM (ASRAM) or synchronous SRAM with a burst feature (SBSRAM). Dynamic RAM may come in one of four types: fast page mode DRAM (FPMDRAM), extended data out DRAM (EDODRAM), extended data out DRAM with a burst feature (BEDODRAM), or synchronous DRAM (SDRAM).
EBSCO illustration.

Although all RAM serves the same basic purpose, there are a number of different varieties. Each type has its own unique characteristics. The RAM most often used in personal computers is a direct descendant of the DRAM invented by Dennard and popularized by companies such as Intel. DRAM is dynamic, meaning that the electrical charge in the memory cells, and thus the stored data, will fade if it is not refreshed often. A common variant of DRAM is speed-focused double data rate synchronous DRAM (DDR SDRAM), the fourth generation of which entered the market in 2014.

RAM that is not dynamic is known as static random-access memory (SRAM). SRAM chips contain many more transistors than their DRAM counterparts. They use six transistors per cell: two to control access to the cell and four to store a single bit of data. As such, they are much more costly to produce. A small amount of SRAM is often used in a computer's central processing unit (CPU), while DRAM performs the typical RAM functions.

Just as the majority of RAM is dynamic, most RAM is also volatile. Thus, the data stored in the RAM will disappear if it is no longer being supplied with electricity—for instance, if the computer in which it is installed has been turned off. Some RAM, however, can retain data even after losing power. Such RAM is known as nonvolatile random-access memory (NVRAM).


RAM works with a computer's other memory and storage components to enable the computer to run more quickly and efficiently, without lagging or freezing. Computer memory should not be confused with storage. Memory is where application data is processed and stored. Storage houses files and programs. It takes a computer longer to access program data stored in ROM or in long-term storage than to access data stored in RAM. Thus, using RAM enables a computer to retrieve data and perform requested functions faster. To improve a computer's performance, particularly when running resource-intensive programs, a user may replace its RAM with a higher-capacity chip so the computer can store more data in its temporary memory.


While RAM typically is used to manage data related to the applications in use, at times it can be used to assist in performing functions that do not usually involve RAM. Certain code, such as a computer's basic input/output system (BIOS), is typically stored within the computer's ROM. However, accessing data saved in ROM can be time consuming. Some computers can address this issue by copying data from the ROM and storing the copy in the RAM for ease of access. RAM that contains code copied from the ROM is known as shadow RAM.

—Joy Crelin

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