Twistor memory
Encyclopedia
Twistor is a form of computer memory
, similar to core memory, formed by wrapping or closing magnetic tape
around a current-carrying wire. Although the developers, Bell Labs
, had high hopes for Twistor, it was used for only a brief time in the marketplace between about 1968 and the mid-1970s. In this period all previous forms of memory were quickly replaced by semiconductor memory
chips, which were considerably faster and less expensive. Twistor is largely the brainchild of a single person, Andrew Bobeck, who later developed bubble memory
after generalizing some of the concepts used in Twistor.
s - the cores - are threaded by two crossed wires, X and Y, to make a matrix known as a plane. When one X and one Y wire are powered, a magnetic field is generated at a 45-degree angle
to the wires. The core magnets sit on the wires at a 45-degree angle, so the single core wrapped around the crossing point of the powered X and Y wires will pick up the induced field.
. This line is shared by all of the cores in a particular plane, meaning that only one bit can be read (or written) at once. Core planes were typically stacked in order to store one bit of a word per plane, and a word could be read or written in a single operation by working all of the planes at once.
, fast compared to earlier systems, and fairly dense. The main concern with core was the time needed to wire up all the small magnets, a task which grew in complexity as the density of the core planes was increased.
. The Y wires were replaced by solenoid
s wrapping a number of twistor wires. Selection of a particular bit was the same as in core, with one X and Y line being powered, generating a field at 45 degrees. The magnetic tape was specifically selected to only allow magnetization along the length of the tape, so only a single point of the twistor would have the right direction of field to become magnetized.
s can be read or written at the same time, because there is no need for a sense/inhibit line. Unlike core, the X and Y lines do not both have to be driven in order to read a bit, instead only the Y is used and the X can be used as the sense line. Each of the X lines in a stack of twistor can then be read at the same time, in a similar fashion to core.
Another advantage to twistor was mechanical; twistor elements could be built using completely automated machines. Typically the magnetic tape was wound around a copper wire, with a stack of such wires being embedded in a PET film
sheet. The sheet could then be folded accordion
-style to make a smaller block, and then inserted through a row of solenoids.
It was this reason that led Bell to spend so much time developing the system, because they believed twistor could lead to considerably lower cost memory systems, leaving them supplying the majority of computer makers. Instead, semiconductor memory systems
"came out of nowhere" as disruptive technology
, and twistor never had time to become established before all core-type systems disappeared.
project.
In the United States the Bell System
(AT&T
) also used twistors with permanent magnets as the "Program Store" or main memory in their first, groundbreaking, electronic telephone switching system, the 1ESS
as well as others in the ESS
series of electronic telephone switches, and did so up to the 4ESS switch
introduced in 1976 and sold into the 1980s.
In addition, Twistor was used in the Traffic Service Position System (TSPS)
, Bell's successor to cord telephone switchboard
s which controlled call handling and coin collection for local and international calls.
As of October, 2008 some remaining TSPS and ESS
installations continue to provide telephone service in rural areas of the United States, as well as Mexico
and Colombia
where many U.S. systems were sold and re-installed after being removed from service in the United States.
Computer memory
In computing, memory refers to the physical devices used to store programs or data on a temporary or permanent basis for use in a computer or other digital electronic device. The term primary memory is used for the information in physical systems which are fast In computing, memory refers to the...
, similar to core memory, formed by wrapping or closing magnetic tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
around a current-carrying wire. Although the developers, Bell Labs
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...
, had high hopes for Twistor, it was used for only a brief time in the marketplace between about 1968 and the mid-1970s. In this period all previous forms of memory were quickly replaced by semiconductor memory
Semiconductor memory
Semiconductor memory is an electronic data storage device, often used as computer memory, implemented on a semiconductor-based integrated circuit. Examples of semiconductor memory include non-volatile memory such as Read-only memory , magnetoresistive random access memory , and flash memory...
chips, which were considerably faster and less expensive. Twistor is largely the brainchild of a single person, Andrew Bobeck, who later developed bubble memory
Bubble memory
Bubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles or domains, each storing one bit of data...
after generalizing some of the concepts used in Twistor.
Construction
In core memory, small annular magnetMagnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
s - the cores - are threaded by two crossed wires, X and Y, to make a matrix known as a plane. When one X and one Y wire are powered, a magnetic field is generated at a 45-degree angle
Angle
In geometry, an angle is the figure formed by two rays sharing a common endpoint, called the vertex of the angle.Angles are usually presumed to be in a Euclidean plane with the circle taken for standard with regard to direction. In fact, an angle is frequently viewed as a measure of an circular arc...
to the wires. The core magnets sit on the wires at a 45-degree angle, so the single core wrapped around the crossing point of the powered X and Y wires will pick up the induced field.
Data Retrieval
In core memory, a third wire - the sense/inhibit line - is needed to write or read a bitBit
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...
. This line is shared by all of the cores in a particular plane, meaning that only one bit can be read (or written) at once. Core planes were typically stacked in order to store one bit of a word per plane, and a word could be read or written in a single operation by working all of the planes at once.
Advantages and disadvantages
Core was non-volatileNon-volatile memory
Non-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...
, fast compared to earlier systems, and fairly dense. The main concern with core was the time needed to wire up all the small magnets, a task which grew in complexity as the density of the core planes was increased.
Twistor
Twistor was similar in concept, but instead replaced the circular magnets with magnetic tape to store the patterns. The tape was wrapped around one set of the wires, say X, in such a way that it formed a 45-degree helixHelix
A helix is a type of smooth space curve, i.e. a curve in three-dimensional space. It has the property that the tangent line at any point makes a constant angle with a fixed line called the axis. Examples of helixes are coil springs and the handrails of spiral staircases. A "filled-in" helix – for...
. The Y wires were replaced by solenoid
Solenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
s wrapping a number of twistor wires. Selection of a particular bit was the same as in core, with one X and Y line being powered, generating a field at 45 degrees. The magnetic tape was specifically selected to only allow magnetization along the length of the tape, so only a single point of the twistor would have the right direction of field to become magnetized.
Advantages
One major advantage of twistor is that the entire row of twistors enclosed by one of the Y solenoidSolenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
s can be read or written at the same time, because there is no need for a sense/inhibit line. Unlike core, the X and Y lines do not both have to be driven in order to read a bit, instead only the Y is used and the X can be used as the sense line. Each of the X lines in a stack of twistor can then be read at the same time, in a similar fashion to core.
Another advantage to twistor was mechanical; twistor elements could be built using completely automated machines. Typically the magnetic tape was wound around a copper wire, with a stack of such wires being embedded in a PET film
PET film (biaxially oriented)
BoPET is a polyester film made from stretched polyethylene terephthalate and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties and electrical insulation.A variety of companies manufacture boPET and other...
sheet. The sheet could then be folded accordion
Accordion
The accordion is a box-shaped musical instrument of the bellows-driven free-reed aerophone family, sometimes referred to as a squeezebox. A person who plays the accordion is called an accordionist....
-style to make a smaller block, and then inserted through a row of solenoids.
It was this reason that led Bell to spend so much time developing the system, because they believed twistor could lead to considerably lower cost memory systems, leaving them supplying the majority of computer makers. Instead, semiconductor memory systems
Random-access memory
Random access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...
"came out of nowhere" as disruptive technology
Disruptive technology
A disruptive technology or disruptive innovation is an innovation that helps create a new market and value network, and eventually goes on to disrupt an existing market and value network , displacing an earlier technology there...
, and twistor never had time to become established before all core-type systems disappeared.
Data Retrieval
Twistor typically included a single plane of core used to select which solenoid to power, as opposed to being used as memory; the single magnetized core fed power into a particular solenoid. This is actually the original purpose of core, to select a single element out of an X and Y grid of powered lines; the concept of using the generated magnetic field as a storage system developed later.Applications
Twistor was used in a number of applications. Much of the development funding was supplied by the US Air Force, as twistor was to be used as the main memory in the Nike XProject Nike
Project Nike was a U.S. Army project, proposed in May 1945 by Bell Laboratories, to develop a line-of-sight anti-aircraft missile system. The project delivered the United States' first operational anti-aircraft missile system, the Nike Ajax, in 1953...
project.
In the United States the Bell System
Bell System
The Bell System was the American Bell Telephone Company and then, subsequently, AT&T led system which provided telephone services to much of the United States and Canada from 1877 to 1984, at various times as a monopoly. In 1984, the company was broken up into separate companies, by a U.S...
(AT&T
AT&T
AT&T Inc. is an American multinational telecommunications corporation headquartered in Whitacre Tower, Dallas, Texas, United States. It is the largest provider of mobile telephony and fixed telephony in the United States, and is also a provider of broadband and subscription television services...
) also used twistors with permanent magnets as the "Program Store" or main memory in their first, groundbreaking, electronic telephone switching system, the 1ESS
1ESS switch
The Number One Electronic Switching System, the first large-scale Stored Program Control telephone exchange or Electronic Switching System in the Bell System, was introduced in Succasunna, New Jersey, in May 1965. The switching fabric was composed of reed matrixes controlled by wire spring relays...
as well as others in the ESS
Electronic switching system
In telecommunications, an electronic switching system is:* A telephone exchange based on the principles of time-division multiplexing of digitized analog signals. An electronic switching system digitizes analog signals from subscriber loops, and interconnects them by assigning the digitized...
series of electronic telephone switches, and did so up to the 4ESS switch
4ESS switch
The 4ESS switch is a Class 4 telephone Electronic Switching System that was the first digital electronic toll switch introduced by Western Electric for long distance switching. It was introduced in 1976 in Chicago, Illinois to replace the 4a crossbar switch. The last of 145 in the AT&T network was...
introduced in 1976 and sold into the 1980s.
In addition, Twistor was used in the Traffic Service Position System (TSPS)
Traffic Service Position System
Traffic Service Position System was developed by Bell Labs in Columbus, Ohio to replace traditional cord switchboards. The first TSPS was deployed in 1969 and used the Stored Program Control-1A CPU, "Piggyback" twistor memory and IGFET Insulated Gate Field Effect Transistor solid state memory...
, Bell's successor to cord telephone switchboard
Telephone switchboard
A switchboard was a device used to connect a group of telephones manually to one another or to an outside connection, within and between telephone exchanges or private branch exchanges . The user was typically known as an operator...
s which controlled call handling and coin collection for local and international calls.
As of October, 2008 some remaining TSPS and ESS
Electronic switching system
In telecommunications, an electronic switching system is:* A telephone exchange based on the principles of time-division multiplexing of digitized analog signals. An electronic switching system digitizes analog signals from subscriber loops, and interconnects them by assigning the digitized...
installations continue to provide telephone service in rural areas of the United States, as well as Mexico
Communications in Mexico
Communications in Mexico are regulated by the Secretariat of Communication and Transportation , a federal executive cabinet ministry and by the Federal Telecommunications Commission .Mexico's communication services market is among the...
and Colombia
Communications in Colombia
Since being liberalized in 1991, the Colombian telecommunications sector has added new services, expanded coverage, improved efficiency, and lowered costs. The sector has had the second largest investment in infrastructure since 1997. However, the economic downturn between 1999 and 2002 adversely...
where many U.S. systems were sold and re-installed after being removed from service in the United States.
External links
- Stress insensitive permalloys for memory application
- Memory Units - a general discussion of computer memory systems written in the late 1960s, which includes a discussion of twistor.
- EETimes - Misunderstood Milestones