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Unformatted text preview: stored in a PROM chip, they can usually be executed in a fraction of
the time previously required. PROMs are ; programmed to record information using a
special device known as PROM-programmer. However, once the chip has been
programmed, the recorded information cannot be changed, i.e., the PROM becomes a
ROM and it/Is only possible to read the stored information. PROM is also non-volatile
storage, i.e., the stored information remains intact even if power is switched off.
Once information is stored in a ROM chip or a PROM chip it cannot be altered.
However, there is another type of memory chip called Erasable Programmable ReadOnly Memory (EPROM) that overcomes this problem. As the name implies, it is possible
to erase information stored in an EPROM chip and the chip can be reprogrammed to store
new information. EPROMs are often used by R&D personnel (experimenters) who
frequently change the microprograms to test the efficiency of the computer system with
new programs. EPROMs are also useful in case of those applications where one may like
to store a program in a ROM, which would normally not change, but under some
unforeseen conditions one may like to alter it. When an EPROM is in use, information
stored in it can only be "read" and the information remains in the chip until it is erased.
EPROM chips are of two types - one in which the stored information is erased by
exposing the chip for some time to ultraviolet light, and the other one in which the stored
information is erased by using high voltage electric pulses. The former is known as Ultra
Voilet EPROM (UVEPROM) and the latter is known as Electrically EPROM
(EEPROM). It is easier to alter information stored in an EEPROM chip as compared to
an UVEPROM chip. This is because to alter information stored in an UVEPROM chip,
the chip has to be removed from the computer, erased using a special ultra-violet rays
emitting device, and then reprogrammed. On the other hand in case of an EEPROM chip,
stored programs can be altered electrically by using special programs, without the chip
being removed from the computer. Due to the ease with which stored programs can be
altered, EEPROM is also known as flash memory. Flash memory is used in many new
I/O and storage devices. The intelligence of these devices can be upgraded by simp...
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This document was uploaded on 04/07/2014.
- Spring '14