Random-access memory

Random-access memory is defined by its ability to access any memory location directly, in any order, with similar access time. This contrasts with sequential-access media like tape, where data must be read in order. RAM is typically volatile, meaning it requires power to retain data; common types include DRAM (dynamic RAM) and SRAM (static RAM). DRAM stores each bit in a capacitor and must be refreshed thousands of times per second, while SRAM uses flip-flops and is faster but more expensive, often used for CPU caches.²

The concept of random access dates to early mechanical devices, but the first practical RAM was magnetic-core memory, developed in the 1950s and used until the 1970s. It stored data using magnetized rings, with each core representing one bit. In 1966, Robert Dennard invented one-transistor DRAM, which became the basis for modern memory chips. This innovation allowed memory to be miniaturized and mass-produced, leading to the semiconductor RAM used in virtually all computers today.

RAM serves as the primary working memory in computers, holding the operating system, application programs, and data currently in use. Its speed and random-access nature enable processors to fetch instructions and data quickly, directly impacting system performance. RAM is also used in embedded systems, networking equipment, and graphics cards (as VRAM). In modern systems, RAM is often paired with virtual memory, which uses disk storage to extend apparent memory capacity, though at much slower speeds.³

Beyond the common DRAM and SRAM, there are niche RAM technologies. For instance, magnetoresistive RAM (MRAM) uses magnetic states to store data, offering non-volatility and high speed, and is used in some aerospace and industrial applications. Another is ferroelectric RAM (FeRAM), which uses a ferroelectric layer and is found in smart cards and RFID tags. Historically, delay-line memory, used in early computers like the UNIVAC, was a form of sequential access, not true RAM, but it influenced later designs. Additionally, RAM can be susceptible to soft errors caused by cosmic rays, a concern in high-altitude and space applications, leading to error-correcting code (ECC) memory.

DRAM

Dynamic random-access memory, which stores each bit in a capacitor and requires periodic refreshing.

SRAM

Static random-access memory, which uses flip-flops and does not need refreshing, but is more expensive.

Volatile memory

Memory that loses its contents when power is removed.

Magnetic-core memory

An early form of RAM using magnetized rings to store bits.