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For offer is a magnetic core memory plane from a 1965-vintage Burroughs main frame computer. It is an array of 60 by 80 cores. So it can store 4800 bits. Physically it's 4-1/2" x 5-3/4".
It's mounted in a plastic holder that can sit on your desk. It's held between two sheets of clear plastic to protect it from dust and still be easily visible. If you desire, the memory plane can be easily removed for close examination. On the back of the memory plane is attached a description of what it is.
Every large computer system from 1955 to 1975 contained a number of memory storage planes similar to this one. This one was made in the USA unlike others on that were made in the USSR one or two decades later. As such this plane is worthy of exhibition in any museum or on your desk.
This core memory plane is in mint-condition and is completely clean. It has sat in a closet since 1969. It wasn't extracted from a piece of equipment that was stored in a dirty humid warehouse for decades.So How Does Magnetic Core Memory Work
Magnetic core memory uses tiny magnetic rings called cores, through which wires are threaded to write and read information. Each core represents one bit of information. The cores can be magnetized in two different ways (clockwise or counterclockwise) and the bit stored in a core is zero or one depending on that core's magnetization direction.
Each core is addressed by an x and a y wire. These are the green wires visible in the photos. A sense wire (orange) detects a change of state and a write inhibit wire (also orange) is used to set a bit to 0 or 1 when written. Cycle time was generally between 6 microseconds and 1 microsecond. See Wikipedia for a good detailed description.
Originally core memory was all handmade at a cost of about $1 per bit. However, the manufacturing process became semi-automated, and the cost declined significantly. Because this memory plane holds 4800 bits, cost might have been as much as $48,000 in today's dollars accounting for inflation. Most likely Burroughs charged something around $4,000 in current dollars new.
History of Magnetic Core Memory
Magnetic core memory was perfected in the 1950's, and it was the predominant large-system memory from 1955 to 1975. Early core memory was handmade and was somewhat irregular in appearance. This core memory is compact and regular indicating that manufacture was semi-automated. Each core is about 1 mm in diameter. Later, core diameter was reduced to 0.8 mm or less to give a faster switching speed.
Core memory was replaced by semiconductor RAM about 1975. Semiconductor RAM is much faster, much more compact, and much less expensive. However unlike semiconductor RAM, magnetic core memory is non-volatile and was used in special systems until flash memory became available.
Burroughs Computers
Someone who worked at Burroughs during the 1960's saw this memory plane and believes that it was used in a B300 or B500 system. These computers supported memory in 4800-character increments. The line started with the B100 system about 1961 and eventually grew into the B100/B200/B300/B500 versions.
The Burroughs B500 was a smaller low-cost general-purpose electronic data processing system with unusually productive capabilities for its size. It was primarily aimed at the business applications market. A typical B500 might have 192 kilobytes of memory, which corresponds to 280 memory planes such as the one offered here. No wonder that a computer back then would fill an entire room.
These computers used character/decimal system (binary coded decimal or BCD) like the IBM 1401. That's why a memory assembly would have seven planes and not eight. This approach made for slight inefficiencies in memory utilization that were compensated for by the resultant simplification of the circuitry and software. Four bits of the seven expressed numbers from 0 to 9. One bit was used as a parity bit, and two bits were available for alphanumeric representation.
This memory plane was purchased from C & H Surplus in Pasadena, California in 1969. Box markings identify it as coming from the Burroughs Corporation at 460 Sierra Madre Villa in Pasadena, California. The Electrodata Division of Burroughs was at this address until it was it was closed about then. Most likely, Burroughs sold out unused parts to C & H Surplus. Probably it was a never-used backup unit intended for system repair.
This your chance to own a piece of computing history
What you see is what you get. Please feel free to contact me for more information or to comment.

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