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Programmable Read-Only Memory (ROM)

Programmable read-only memory, a read-only memory (ROM)of merely one-time modification by the user, is a kind of computer storage memory chip that allows the hardware called the PROM programmer to write data into the device.


It is only allowed to write once, so it is also called "one-time programmable" device. When it is shipped from the factory, the contents of the programmable read-only memory are all 1s. The user can write some of these units to the data 0 as needed to realize their "programming" purpose. The typical product of PROM is a "bipolar fuse structure". If we want to rewrite some units, we can give these units a current large enough and maintain it for some time to fuse the wire, so that the effect of rewriting some bits is achieved. Another class of classic programmable read-only memory is the PROM that uses "Schottky diode". When leaving the factory,  the diode is in a reverse cut off state, or a large current method is added to the "Schottky diode" to cause the permanent breakdown.


The new programmable read-only memory chip is blank, but it's preloaded into the binary 1. The 1Mbit ROM chip used by the computer has 1 million (in fact 1048576 bits) bits, each holding 1 binary. The blank PROM is programmable or written to it. A special machine device is needed called a programmer, or a ROM programmer, or a ROM feeder, for writing. The process of programming PROM takes time from a few seconds to a few minutes, depending on the size of the chip and the use of the programming device.
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