ICT Lecture 2: Memory Unit
A memory unit is the collection of storage
units or devices together. The memory unit stores the binary information in the
form of bits. Generally, memory is classified into two categories:
·
Volatile Memory: This loses its data, when power is switched off.
Figure1 : Memory Hierarchy
Important Points:
The
speed and cost increases from bottom to top i.e. from secondary memory to
register.
The
size and access time increases from top to bottom i.e. from register to
secondary memory.
Cache Memory
It is used to store programs or data currently being
executed or temporary data frequently used by the CPU. It has very high speed. Its
size is normally kept small because bigger size of cache memory is very
expensive.
Registers
These are local to CPU to processes data and instruction
with high speed. So, the computer uses a number of special memory units called
registers. They are not part of the main memory but they store data or
information temporarily and pass it on as directed by the control unit.
Types of Memory
Memory
can be primary or secondary.
Primary
memory includes RAM and ROM. Secondary Memory includes magnetic tape, hard
disk, Floppy Disk, CD (Compact Disk) /DVD (Digital Versatile Disc) ROM, Flash
Drive.
Figure
2: Types of Primary Memory
RAM
(Random Access Memory)
It is volatile (or
temporary) memory which means data in RAM
disappears from it as soon as the power to the computer is switched off. It has two types: Static RAM (SRAM) or Dynamic RAM (DRAM).
ROM
(Read Only Memory)
It is non-volatile memory
which means the storage of program and data in the
ROM is permanent. The contents of ROM can only be read by the CPU but it cannot
be changed. It can be further
classified as PROM, EPROM, EEPROM.
PROM (Programmable Read Only Memory)
It is possible to store
your program in PROM chip. Once the programs are written it cannot be changed.
As it is non-volatile memory, so content remain intact even if power is
switched off.
EPROM (Erasable
Programmable Read Only Memory)
EPROM overcomes the problem
of ROM and PROM. EPROM chip can be programmed time and again by erasing the
information stored earlier in it by using Ultraviolet light.
EEPROM (Electrically Erasable Programmable Read Only Memory)
EEPROM provides the same facility as provided by EPROM. The
only difference is that the information is deleted by electrical signals
instead of ultraviolet light.
Previous Year Question from topic discussed above:
1. Which of the following correctly lists computer memory types from
highest to lowest speed ? (January 2017)
(1) Secondary Storage; Main Memory
(RAM); Cache Memory; CPU Registers
(2) CPU Registers; Cache Memory;
Secondary Storage; Main Memory (RAM)
(3) CPU Registers; Cache Memory;
Main Memory (RAM); Secondary Storage
(4) Cache Memory; CPU Registers; Main
Memory (RAM); Secondary Storage
Answer:
Option (3) is correct
2. Random Access Memory
(RAM), a form of computer storage, is a ______ memory. (August 2016)
(1) Non-volatile (2)
Volatile
(3) Permanent (4) Secondary
(3) Permanent (4) Secondary
Answer:
Option (2) is correct
3. _________ is a type of memory circuitry that holds the computer’s
start-up routine. (July 2016)
(1) RIM (Read
Initial Memory)
(2) RAM (Random Access Memory)
(3) ROM (Read Only Memory)
(4) Cache Memory
(2) RAM (Random Access Memory)
(3) ROM (Read Only Memory)
(4) Cache Memory
Answer: Option (3) is correct
4. RAM means: (Dec
2007)
(A) Random Access Memory
(B) Rigid Access Memory
(C) Rapid Access Memory
(D) Revolving Access Memory
Answer: Option (A) is correct
5. CD ROM stands for: (Dec 2007)
(A) Computer Disk Read Only Memory
(B) Compact Disk Read Over Memory
(C) Compact Disk Read Only Memory
(D) Computer Disk Read Over Memory
Answer: Option (C) is correct
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