Friday, November 23, 2007


ROM, Read only Memory
The data or information stored in these types of memories is not changeable. It therefore does not require electrical power to retain information. The ROM chip or IC contains rows and columns of diodes. The presence or absence of diode in a particular row defines weather it is a binary one or zero. The content of a ROM is permanent and care has to be taken while designing it. It is not possible to rewrite a ROM. If change is necessitated, the whole chip has to be discarded. But once properly designed, they are robust , consume less power and cheap to manufacture.
The different types of ROM are:
1.PROM , Programmable Read only MemoryThe design of ROM is made easier by the PROM. PROM contains a fuse at the junction of each row and column of the grid. In the initial stage the complete grid represents a binary one. When an electric charge is passed through it, it ruptures the fuse and becomes a zero.
2.EPROM Erasable Programmable Read only MemoryThis is an improvement on PROM. Ultraviolet light is used to erase the information. This is a tedious process and excess exposure may lead to destruction of the ROM.
3.EEPROM , Electrical Erasable Programmable Read only MemoryThis kind of ROM is popular in memory sticks. The required portion of the memory can be erased or written on in a selective basis.
By: Victor Epand

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