Memory Cores

Verified Timeline

Lore & Background

The basic concept of using the square hysteresis loop of certain magnetic materials as a storage or switching device was known from the earliest days of computer development. J. Presper Eckert and Jeffrey Chuan Chu did some development work on the concept in 1945 at the Moore School during the ENIAC efforts. Robotics pioneer George Devol filed a patent for the first static (non-moving) magnetic memory on 3 April 1946. Frederick Viehe applied for various patents on the use of transformers for building digital logic circuits beginning in 1947. A fully developed core system was patented in 1947, and later purchased by IBM in 1956. Substantial work was carried out by An Wang and Way-Dong Woo, who created the pulse transfer controlling device in 1949. The patent described a type of memory that would today be known as a delay-line or shift-register system. MIT computer engineer Jay Forrester received the principal patent for his invention of the coincident-current core memory that enabled the 3D storage of information. The first core memory of 32 × 32 × 16 bits was installed on the Whirlwind computer in the summer of 1953. William Papian stated: 'Magnetic-Core Storage has two big advantages: (1) greater reliability with a consequent reduction in maintenance time devoted to storage; (2) shorter access time (core access time is 9 microseconds: tube access time is approximately 25 microseconds), thus increasing the speed of computer operation.'

In Their Own Story

The helmet light cut through the murky darkness of the Archives, illuminating floating dust motes in the stagnant water. A low hum vibrated against the suit's hull as the terminal flickered to life, its interface displaying an ancient language that slowly translated on the PDA screen. There, suspended in a magnetic field, was the core—a pulsing blue crystal containing the final thoughts of a dead race. The survivor reached out, knowing this single object held the key to survival, and perhaps, redemption.

Reader's Guide

Magnetic-core memory was almost universal until the introduction of the first semiconductor memory chips in the late 1960s, and especially dynamic random-access memory (DRAM) in the early 1970s. Initially around the same price as core, DRAM was smaller and simpler to use. Core was driven from the market gradually between 1973 and 1978. Even after magnetic-core memory was replaced by semiconductor memory, main memory was often still referred to as 'core', particularly by people used to the term who worked on older machines with magnetic-core memory. The process of copying the entire content of a computer's main memory to a disk file for further inspection by a system programmer is still called a 'core dump'. When core memory used for calculations was expensive and a scarce resource, technologies were developed to swap blocks of data 'out of core' onto larger, slower storage. Algorithms whose working set size exceeds main memory came to be called out-of-core algorithms, while in-core algorithms fit in main memory. Using smaller cores and wires, the memory density of core slowly increased. By the late 1960s, a density of about 32 kilobits per cubic foot (about 0.9 kilobits per litre) was typical. The cost declined from about $1 per bit to about 1 cent per bit. Reaching this density requires extremely careful manufacturing, which was almost always carried out by hand in spite of repeated major efforts to automate the process.

Did You Know?

• The first core memory of 32 × 32 × 16 bits was installed on the Whirlwind computer in the summer of 1953.
• Core memory is a type of non-volatile memory; when not being read or written, the cores maintain the last value they had, even if the power is turned off.
• Read-only core rope memory was used on the mission-critical Apollo Guidance Computer essential to NASA's successful Moon landings.
• By the late 1960s, a density of about 32 kilobits per cubic foot (about 0.9 kilobits per litre) was typical for core memory.
• The cost of core memory declined from about $1 per bit to about 1 cent per bit over its production period.