Page 46 - DCAP101_BASIC_COMPUTER_SKILLS

Unit 3: Memory

it is possible to erase information stored in an EPROM chip and the chip can be reprogrammed Notes
to store new information. EPROMs are often used by R&D personnel (experimenters) who
frequently change the micro-programs to test the efficiency of a computer system with new
programs. EPROMs are also useful for those applications in which one may like to store a
program in a ROM that 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 of ultraviolet light and the other one in which the stored information
is erased by using high voltage electric pulses is known as Ultra Violet EPROM ((UVEPROAM)
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. EPROM is also known as flash
memory because of the ease with which programs stored in it can be altered. Flash memory
is used in many new 1/O and storage devices like USB (Universal Serial Bus) pen drive and
MP3 music player.

Figure 3.4: Erasable Programmable Only Memory (EPROM)

3.2.5 Cache Memory

Use of main memory helps in minimizing disk-processor speed mismatch to a large extent
because the rate of data fetching by a computer’s CPU from its main memory is about 100
times faster than that from a high-speed secondary storage like disk. However, even with
the use of main memory, memory-processor speed mismatch becomes a bottleneck in the
speed with which the CPU can process instructions because there is a 1 to 10 speed mismatch
between the processor and memory. That is, the rate at which data can be fetched from
memory is about 10 times slower than the rate at which CPU can process data. Obviously,
the overall performance of a processor can be improved greatly by minimizing the memory-
processor speed mismatch. Cache memory (pronounced “cash” memory) is commonly used
for this purpose. It is an extremely fast, small memory between CPU and main memory
whose access time is closer to the processing speed of CPU. It acts as a high-speed buffer
between CPU and main memory and is used to temporarily store very active data and
instructions during processing. Since cache memory is faster than main memory, processing
speed is improved by making the data and instructions needed for current processing
available in the cache. Cache memory is an extremely fast and small memory between CPU
and main memory. Its access time is closer to the processing speed of CPU. It acts as a high-
speed buffer between CPU and main memory and is used to temporarily store very active
data and instructions during processing.

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