- In full:
- random-access memory
- Key People:
- Jay Wright Forrester
RAM
What are the two types of RAM used in computers?
Why is RAM essential for computer operation?
What advancements have been made in RAM technology?
RAM, computer memory in which specific contents can be accessed (read or written) directly by the central processing unit (CPU) in a very short time regardless of the sequence in which they were recorded. This differs from read-only memory (ROM), which stores data that normally cannot be modified during regular computer operation. Both RAM and ROM are examples of primary memory, which is available to the CPU via direct connections on the motherboard.
Two types of random-access memory are used in computers: static RAM (SRAM) and dynamic RAM (DRAM). A single memory chip is made up of several million memory cells that store a binary digit (0 or 1), or bit—the fundamental unit of computer memory. In an SRAM chip each memory cell stores a bit for as long as power is supplied. In a DRAM chip the charge on individual memory cells must be refreshed periodically to retain data. Because it has fewer components, DRAM requires less chip area than SRAM. Hence, a DRAM chip can hold more memory than an SRAM chip can.
Bits are the fundamental unit of memory. Eight bits make up the more familiar byte. Data storage scales in multiples of 1024: 1024 bytes make a kilobyte (KB), 1024 KB make a megabyte (MB), and so on for each successive unit.
Function
Every time a program is run on it, a computer uses its central processing unit (CPU) to draw the application’s data from storage so it can process it and execute the program. The CPU needs rapid access to that data while programs are active so that they stay responsive. Permanent storage devices such as hard disk drives (HDDs) and solid-state drives (SSDs) store this data in files and, unlike RAM and ROM, are examples of secondary memory—they are not directly connected to the CPU. They have complex, layered arrays of memory chips to hold large amounts of data, and they keep access to it even when the power supply is turned off. But drawing information from them is impractical for executing programs, because the rate of data transfer between the CPU and an SSD (the faster of the two permanent storage options) is much slower than the speed at which the CPU operates.
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This is where RAM becomes essential. Application data is first loaded into RAM from permanent storage before the CPU processes it. Dynamic RAM (DRAM), the most common type of RAM used in computers, typically comes in the form of memory modules packed into a rectangular assembly called a stick that contains a row of contact points that attach directly into dedicated slots in the computer’s motherboard, though DRAM can also be soldered on. RAM is built on a smaller scale than HDDs or SSDs, with a relatively simple two-dimensional array of chips so that the CPU can easily locate information rather than search in a large block of chips arranged in many rows and columns.
RAM acts as a fast working area between the CPU and long-term storage. RAM organizes data into memory locations identified by unique addresses, allowing the CPU to directly and quickly access the required information regardless of sequence, which is why RAM is called “random-access” memory. This allows RAM to provide much lower latency and far higher data transfer speeds than HDDs or SSDs and enables the CPU to process instructions efficiently and keep programs responsive. Memory-intensive programs tend to run slower or less efficiently when RAM is overused or insufficient. RAM is considered volatile memory because it only retains data while the computer is powered on. Unlike HDDs or SSDs, which store data permanently, RAM is designed for speed rather than long-term storage.
But DRAM is not fast enough for the CPU’s most time-sensitive operations. Therefore, modern processors contain smaller amounts of static RAM (SRAM) built directly into the CPU as cache memory, which the CPU uses to store frequently accessed instructions and data, reducing delays and improving processing speed. SRAM operates much faster than DRAM because it does not require periodic refreshing to retain data. However, SRAM is more expensive and less space-efficient than DRAM, so it is used only in limited quantities.
History
RAM technology has evolved alongside advances in computing hardware. Early personal computers commonly used single in-line memory modules (SIMMs), which featured contact pins on one side of the module and could transfer up to 32 bits at a time per module. These were later replaced by dual in-line memory modules (DIMMs), which had pins on both sides and provided wider data paths and improved performance. DIMMs became the standard memory module format for desktop computers and servers, whereas small-outline DIMMs (SO-DIMMs) were developed for laptops and other compact devices.
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The Williams-Kilburn tube, developed in 1947 by Frederic C. Williams, Tom Kilburn, and Geoff Tootill, was the first practical electronic random-access memory. It used cathode-ray tubes to store data as electrostatic charge patterns that required constant refreshing. The technology enabled the creation of the Manchester Baby, the first electronic computer to run programs stored in memory, in 1948.
During the 1990s synchronous dynamic RAM (SDRAM) became widely adopted because it synchronized memory operations with the computer’s system clock. SDRAM was followed by double data rate synchronous dynamic RAM (DDR-SDRAM), which increased efficiency by transferring data twice during each clock cycle instead of once.
Successive generations—DDR2, DDR3, DDR4, and DDR5—have provided progressively higher transfer speeds, greater bandwidth, larger capacities, and lower power consumption. DDR4 became widely used in personal computers and servers during the 2010s, and DDR5 introduced further improvements for artificial intelligence, gaming, and high-performance computing systems. These developments in RAM technology have enabled faster multitasking, smoother application performance, and support for increasingly complex software applications.
