Read Only Memory(ROM)

Read Only Memory(ROM)

ROM is a permanent type of memory. Its contents are not lost even when power supply is switched off. However,the user cannot write into a ROM. Its contents are written into at manufacturing time. ROM stores permanent programs and other type of data which are needed by the computer to execute user programs. they store function, such as sine, cosine, logarithm, square root,exponential and code conversion table, etc.

Programmable Read Only Memory (PROM)

Programmable ROM are also available. Different types of PROM such as erasable PROM is called E PROM, while electrically erasable PROM is called E E PROM. User can write information in PROM, E PROM and E E PROM. Once programmed, the recorded information in an E PROM or E E PROM can be erased to record different information , whereas in a POM the information once written by the user cannot be changed. such information is needed while executing user program. 

Erasable Programmable Read Only Memory (E PROM)

The stored data in E PROM can be erased by exposing them to high-intensity short wave ultraviolet light for about 20 minutes. When an E PROM is exposed to ultraviolet light, the entire data is erased. E PROM are cheap, reliable and hence they are widely used. they can store programs which are permanent but need updating. The programs which are at the research and development stage also need to be stored in E PROM because they are modified several times. Where updating or changes in programs at the development stages are required, E PROM are far more economical than PROM because they can be reused.

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