Memory in a computer is required
for storage and subsequent retrieval of the in the instruction and data . A
computer system uses variety of devices for storing these instructions and data
which are required for its operations.
“The storage devices along with the algorithm or information on how to control and manage these storage
devices constitute the memory system of a computer.”
Memory system
Memory system is a very simple system yet it exhibits a wide range of
technology and its types. The basic objective of a computer system is to
increase the speed of computation. Likewise the basic objective of a memory
system is to provide fast uninterrupted access by the processor to the memory such that the processor can
operate at the speed it is expected to work.
A memory system can be considered to consist of the three group of
memories. These are:
Secondary/auxiliary memory
Auxiliary memory infect is much
larger in size than main memory but is slower than main memory .It
normally stores system programs,
instructions and data files. Secondary memory can also be used as an overflow
memory in case the main memory capacity has been exceeded. Secondary memories
can not be accessed directly by a processor. First the information of these
memories is transferred to the main memory and then the information can be
accessed as the information of main memory.
Characteristics Terms of Memory Systems
The following terms are most commonly used for identifying
comparative behavior of various memory devices and technologies :
1)Storage Location:3 possible storage
locations are: a)Internal storage: We
define internal storage which is
needed all the time and located inside also called primary storage .
b)External storage: We define this storage
which is located outside of CUP but connected to CUP. It is also called
secondary storage.
2.Storage capacity:
It is the amount of data that can be stored in the storage
unit. The storage capacity can be expressed in terms of bytes.
a)Bit :A binary digit is local 0 or 1
representing called a passive or an active state of a component in an electric
circuit.
b)Nibble: A group of 4 bits is called a
nibble.
c) Byte: A group of 8 bits is called byte.
A byte is the smallest unit which can represent a data item or a character.
3) Unit of transfer:
Unit of transfer can a word or block. For internal memory, generally a
unit of transfer is equal to the word length. For external memory, data are
often transferred in much larger units than a word and these are referred to as
a blocks.
4)Performance : These are performance
parameters:
a)Access Time :Access time is defined as
time required to locate and retrieve a record.
b)Access rate: Access rate is defined as
no. of read/ write operations carried out per second.
5)Access Method:
Access refers to the way the memory can be addresses or recorded
information can be accessed.
6)Physical type:
A variety of physical types of memory have
been employed. The two most common types today are semiconductor or magnetic
memory.
7)Physical characteristic: various physical
characteristic are:
1)Destructive read out:
In this type the contents are read, they
are wiped out . This is called destructive read out. Magnetic core memories are
such memories.
2)Dynamic Memories: In this type ,memory
has the property that they tend to decay. Some semiconductor memory come into
this category. The soln is Refreshing
3)Volatile memories: These are those where
information are lost when power is turned off. Semiconductor memories are of
this type. The solution to the problem is using of UPS.
Submitted by:kamaljeet kaur
Class:B.Sc.(com.sci.)1st
Roll no.:4214
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