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Programmable read-only memory

 
Programmable Read Only Memory

 
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Programmable read-only memory
 
 
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A programmable read-only memory (PROM) or field programmable read-only memory (FPROM) is a form of digital memory where the setting of each bit is locked by a fuse
Fuse (electrical)

In electronics and electrical engineering a fuse is a type of overcurrent protection device. Its essential component is a metal wire or strip that melts when too much current flows, which breaks the electrical network in which it is connected, thus protecting the circuit's other components from damage due to excessive current....
 or antifuse
Antifuse

An antifuse is an electrical device that performs the opposite function to a Fuse . Whereas a fuse starts with a low resistance and is designed to permanently break an Electrical conduction path , an antifuse starts with a high resistance and is designed to permanently create an electrically conductive path ....
. Such PROMs are used to store programs permanently. The key difference from a strict ROM
Read-only memory

Read-only memory is a class of computer storage media used in computers and other electronic devices. Because data stored in ROM cannot be modified , it is mainly used to distribute firmware ....
 is that the programming is applied after the device is constructed.






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D23128c Prom
A programmable read-only memory (PROM) or field programmable read-only memory (FPROM) is a form of digital memory where the setting of each bit is locked by a fuse
Fuse (electrical)

In electronics and electrical engineering a fuse is a type of overcurrent protection device. Its essential component is a metal wire or strip that melts when too much current flows, which breaks the electrical network in which it is connected, thus protecting the circuit's other components from damage due to excessive current....
 or antifuse
Antifuse

An antifuse is an electrical device that performs the opposite function to a Fuse . Whereas a fuse starts with a low resistance and is designed to permanently break an Electrical conduction path , an antifuse starts with a high resistance and is designed to permanently create an electrically conductive path ....
. Such PROMs are used to store programs permanently. The key difference from a strict ROM
Read-only memory

Read-only memory is a class of computer storage media used in computers and other electronic devices. Because data stored in ROM cannot be modified , it is mainly used to distribute firmware ....
 is that the programming is applied after the device is constructed. They are frequently seen in video game console
Video game console

A video game console is an game development that produces a video signal which can be used with a display device to display a video game. The term "video game console" is used to distinguish a machine designed for consumers to buy and use solely for playing video games from a personal computer, which has many other functions, or arcade machi...
s, or such products as electronic dictionaries, where PROMs for different languages can be substituted.

Programming

A typical PROM comes with all bits reading as 1. Burning a fuse during programming causes its bit to read as 0. The memory can be programmed just once after manufacturing by "blowing" the fuses (using a PROM blower), which is an irreversible process. Blowing a fuse opens a connection while blowing an antifuse closes a connection (hence the name). Programming is done by applying high-voltage pulses which are not encountered during normal operation (typically 12 to 21 volt
Volt

The volt is the SI SI derived unit of electric potential difference or electromotive force, commonly known as voltage. It is named in honor of the Lombard physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery ....
s). Read-only means that, unlike the case with conventional memory, the programming cannot be changed (at least not by the end user).

Advantages
  • Reliability
  • Stores data permanently
  • Moderate price
  • Built using integrated circuits, rather than discrete components.
  • Fast: reading is between 35ns and 60ns.


Invention


PROM was invented in 1956 by Wen Tsing Chow
Wen Tsing Chow

Wen Tsing Chow , , was a Chinese people-born United States missile guidance scientist and a digital computer pioneer.He received a B.S. in Electrical Engineering from Shanghai Jiaotong University in 1940 and an M.S....
, working for the Arma Division of the American Bosch Arma Corporation in Garden City
Garden City, New York

Garden City is a Political subdivisions of New York State#Village in central Nassau County, New York, New York, in the United States, which was founded by multi-millionaire Alexander Turney Stewart in 1869....
, New York
New York

The State of New York is a U.S. state in the Mid-Atlantic States and Northeastern United States regions of the United States and is the nation's List of U.S....
. The invention was conceived at the request of the United States Air Force
United States Air Force

The United States Air Force is the aerial warfare branch of the Military of the United States and one of the uniformed services of the United States....
 to come up with a more flexible and secure way of storing the targeting constants in the Atlas E/F ICBM's airborne digital computer. The patent and associated technology was held under secrecy order for several years while the Atlas E/F was the main operational missile of the United States ICBM force. The term "burn," referring to the process of programming a PROM, is also in the original patent, as one of the original implementations was to literally burn the internal whiskers of diodes with a current overload to produce a circuit discontinuity. The first PROM programming machines were also developed by Arma engineers under Mr. Chow's direction and were located in Arma's Garden City lab and Air Force Strategic Air Command
Strategic Air Command

The Strategic Air Command was both a major command in the United States Air Force and a "specified command" in the United States Department of Defense....
 (SAC) headquarters.

External links


  • View the US "Switch Matrix" Patent #3028659 at or