Lecture-7
Characteristics of Memory:
In the broad sense, a microcomputer memory system can be
logically divided into three groups:
1) Processor memory
2) Primary or main memory
3) Secondary memory
Processor memory refers to a set of internal registers. These
registers hold temporary results when computation is in progress.
There is no speed disparity between these internal registers and the
microprocessor because they are fabricated on the same chip using
the same technology.
Primary memory or the main memory is the external memory to
store both program and data. The processor can access these
memories directly. In earlier days, the primary memory was designed
using magnetic cores. In modern microprocessors, MOS technology
is employed in the primary memory design. Usually, the size of
primary memory is much larger than the processor memory but its
operating speed is slower than that of the processor registers by a
factor of 25 or 30.
Secondary memory refers to the storage medium compositing
slow devices such as hard disks and floppies. These devices are
used to hold large data and huge program that are not needed by the
processor frequently. Sometimes, secondary memories are also
referred to as auxiliary or back up storage.
In order to design an efficient memory system, the following
characteristics of memory must be known:
, 1. Volatile or Non-volatile
2. Cost
3. Access time and cycle time
4. Access mode
5. Storage type
An important characteristic of a memory is whether it is volatile or
non volatile. The contents of volatile memory are lost if the power is
turned off. On the other hand, a non volatile memory retains its
contents after the power is switched off. The best known non volatile
memory is magnetic core.
The most important factor of a memory system is its cost,
expressed in dollars per bit. A good design implies a very low cost
per bit. Earlier the cost of memory was high but with the development
in VLSI the cost has drastically reduced.
There are two parameters that will indicate the speed with
which information can be transferred in and out of a memory.
1) Access time, tA
2) Cycle time, tC
The access time ‘tA’ is defined as the average time taken to
read a unit of information from the memory. Sometimes the access
time is also referred to as read access time. Similarly, one can define
write access time. Usually, the write access time will be equal to read
access time. The cycle time ‘tC’ of a memory unit is defined as the
average time lapse between two successive read/write operations.
The reciprocal of access time is called the access rate (=1/t A),
which is expressed in bits per second. Similarly, the reciprocal of
Characteristics of Memory:
In the broad sense, a microcomputer memory system can be
logically divided into three groups:
1) Processor memory
2) Primary or main memory
3) Secondary memory
Processor memory refers to a set of internal registers. These
registers hold temporary results when computation is in progress.
There is no speed disparity between these internal registers and the
microprocessor because they are fabricated on the same chip using
the same technology.
Primary memory or the main memory is the external memory to
store both program and data. The processor can access these
memories directly. In earlier days, the primary memory was designed
using magnetic cores. In modern microprocessors, MOS technology
is employed in the primary memory design. Usually, the size of
primary memory is much larger than the processor memory but its
operating speed is slower than that of the processor registers by a
factor of 25 or 30.
Secondary memory refers to the storage medium compositing
slow devices such as hard disks and floppies. These devices are
used to hold large data and huge program that are not needed by the
processor frequently. Sometimes, secondary memories are also
referred to as auxiliary or back up storage.
In order to design an efficient memory system, the following
characteristics of memory must be known:
, 1. Volatile or Non-volatile
2. Cost
3. Access time and cycle time
4. Access mode
5. Storage type
An important characteristic of a memory is whether it is volatile or
non volatile. The contents of volatile memory are lost if the power is
turned off. On the other hand, a non volatile memory retains its
contents after the power is switched off. The best known non volatile
memory is magnetic core.
The most important factor of a memory system is its cost,
expressed in dollars per bit. A good design implies a very low cost
per bit. Earlier the cost of memory was high but with the development
in VLSI the cost has drastically reduced.
There are two parameters that will indicate the speed with
which information can be transferred in and out of a memory.
1) Access time, tA
2) Cycle time, tC
The access time ‘tA’ is defined as the average time taken to
read a unit of information from the memory. Sometimes the access
time is also referred to as read access time. Similarly, one can define
write access time. Usually, the write access time will be equal to read
access time. The cycle time ‘tC’ of a memory unit is defined as the
average time lapse between two successive read/write operations.
The reciprocal of access time is called the access rate (=1/t A),
which is expressed in bits per second. Similarly, the reciprocal of
