Core rope memory
Encyclopedia
Core rope memory is a form of read-only memory
(ROM) for computer
s, first used by early NASA
Mars
probe
s and then in the Apollo Guidance Computer (AGC)
designed and programmed by the MIT
Instrumentation Lab and built by Raytheon
.
Contrary to ordinary coincident-current magnetic core memory
, which was used for RAM at the time, the ferrite
cores in a core rope are just used as transformer
s. The signal from a word line wire passing through a given core is coupled to the bit
line wire and interpreted as a binary "one" while a word line wire that bypasses the core is not coupled to the bit line wire and is read as a "zero". In the AGC, up to 64 wires could be passed through a single core.
Software written by MIT programmers was woven into core rope memory by female workers in factories. Some programmers nicknamed the finished product LOL memory, for Little Old Lady memory.
Read-only memory
Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
(ROM) for computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
s, first used by early NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
probe
Space probe
A robotic spacecraft is a spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe. Many space missions are more suited to telerobotic rather than crewed operation, due to...
s and then in the Apollo Guidance Computer (AGC)
Apollo Guidance Computer
The Apollo Guidance Computer provided onboard computation and control for guidance, navigation, and control of the Command Module and Lunar Module spacecraft of the Apollo program...
designed and programmed by the MIT
Massachusetts Institute of Technology
The Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
Instrumentation Lab and built by Raytheon
Raytheon
Raytheon Company is a major American defense contractor and industrial corporation with core manufacturing concentrations in weapons and military and commercial electronics. It was previously involved in corporate and special-mission aircraft until early 2007...
.
Contrary to ordinary coincident-current magnetic core memory
Magnetic core memory
Magnetic-core memory was the predominant form of random-access computer memory for 20 years . It uses tiny magnetic toroids , the cores, through which wires are threaded to write and read information. Each core represents one bit of information...
, which was used for RAM at the time, the ferrite
Ferrite (magnet)
Ferrites are chemical compounds consisting of ceramic materials with iron oxide as their principal component. Many of them are magnetic materials and they are used to make permanent magnets, ferrite cores for transformers, and in various other applications.Many ferrites are spinels with the...
cores in a core rope are just used as transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...
s. The signal from a word line wire passing through a given core is coupled to the bit
Bit
A bit is the basic unit of information in computing and telecommunications; it is the amount of information stored by a digital device or other physical system that exists in one of two possible distinct states...
line wire and interpreted as a binary "one" while a word line wire that bypasses the core is not coupled to the bit line wire and is read as a "zero". In the AGC, up to 64 wires could be passed through a single core.
Software written by MIT programmers was woven into core rope memory by female workers in factories. Some programmers nicknamed the finished product LOL memory, for Little Old Lady memory.
Memory density
A relatively large (by the standards of the time) amount of data could be stored in a small installed volume of core rope memory (72 kilobytes per cubic foot; roughly 2.5 megabytes per cubic meter); about 18-fold the amount of data per volume compared to standard read-write core memory.| Memory technology |
Data units per cubic foot | Data units per cubic meter | ||
|---|---|---|---|---|
| Bytes | Bits | Bytes | Bits | |
| Core rope ROM | 72 KB | 576 Kbit | ~2.5 MB | ~20 Mbit |
| Magnetic core RAM | 4 KB | 32 Kbit | ~140 KB | ~1 Mbit |
External links
- Visual Introduction to the Apollo Guidance Computer, part 3: Manufacturing the Apollo Guidance Computer. – By Raytheon; hosted by the Library of the California Institute of Technology's History of Recent Science & Technology site (originally hosted by the Dibner Institute)
- Computers in Spaceflight: The NASA Experience – By James Tomayko (Chapter 2, Part 5, "The Apollo guidance computer: Hardware")