1.5.1 Definition and function of memory
Memory is a computer storage system
used to store data, instructions, and results either temporarily or
permanently during processing.
The function of
memory is to store data, instructions, and results for use by the CPU during
processing so that the CPU can work efficiently.
Type of Memory
a. Primary memory and
b. Secondary memory
1.5.2 Units of
memory measurement
Computer memory and storage are
measured in bits and bytes.
|
Unit |
Symbol |
Description |
|
Bit |
b |
The smallest unit
of memory, stores either 0 or 1 |
|
Nibble |
— |
A group of 4
bits. |
|
Byte |
B |
A group of 8
bits, represents one character (e.g., a letter/number). |
|
Kilobyte |
KB |
1024 bytes |
|
Megabyte |
MB |
1024 KB |
|
Gigabyte |
GB |
1024 MB |
|
Terabyte |
TB |
1024 GB |
1.5.3 Types of
memory: primary and secondary memory and their comparison.
Primary memory
(Main Memory / Internal Memory)
Primary memory is the main memory of a
computer system that stores data and instructions currently being used
by the CPU. It is directly accessed by the CPU and is used during
the processing of data.
Secondary memory,
(Storage devices or auxiliary or backup memory)
Secondary memory is a type of memory used to store
data and instructions permanently for future use. It has a large storage
capacity, is not directly accessed by the CPU, and retains data even
when the power is switched off.
|
Primary Memory |
Secondary Memory |
|
Primary memory is
the main memory of a computer used to store data and instructions currently
needed by the CPU. |
Secondary memory is
used to store data and instructions permanently for future use. |
|
Directly accessed
by the CPU |
Not directly
accessed by the CPU |
|
Very fast |
Slower compared to
primary memory |
|
Limited storage
capacity |
Very large storage
capacity |
|
Mostly volatile
(data is lost when power is off) |
Non-volatile (data
is not lost when power is off) |
|
Examples: RAM, ROM,
Cache, Register |
Examples: Hard
Disk, SSD, Pen Drive, CD/DVD |
1.5.4 Example of
primary memory: RAM, ROM, Cache, Register
Types of Primary
Memory:
1. RAM (Random
Access Memory)
RAM is a temporary memory that stores data
and instructions currently being used by the CPU. It is volatile in
nature, so data is lost when the power is switched off.
2. ROM (Read Only
Memory)
ROM (Read Only
Memory) is a non-volatile memory that permanently stores instructions needed to
start the computer and load the operating system. It is non-volatile,
meaning data is not lost when the power is turned off.
Programs stored in
ROM are written during manufacturing and are known as firmware, such as
the BIOS (Basic Input Output System), which helps in booting the
computer.
3. Cache Memory
Cache memory is a very fast memory that
stores frequently used data and instructions to improve the performance
of the CPU. It is located between the CPU and main memory and reduces
the time required to access data.
4. Register
Registers are the
smallest and fastest memory units located inside the CPU that temporarily store
data and instructions during processing.
|
RAM (Random
Access Memory) |
ROM (Read Only
Memory) |
|
RAM is a temporary
memory that stores data and instructions currently used by the CPU. |
ROM is a permanent
memory that stores instructions needed to start the computer and load the
operating system. |
|
It is volatile
in nature, so data is lost when the power is switched off. |
It is non-volatile,
meaning data is not lost when the power is turned off. |
|
Used during
processing |
Used during startup |
|
Faster than ROM |
Slower than RAM |
|
Data can be read
and written |
Data is mostly
read-only |
Types of RAM
1. DRAM (Dynamic
Random Access Memory)
DRAM is a type of RAM
that stores data temporarily and needs to be refreshed repeatedly
to retain data. It is slower than SRAM but has a larger storage
capacity and is commonly used as the main memory of a computer.
2. SRAM (Static
Random Access Memory)
SRAM is a type of RAM
that stores data without frequent refreshing. It is faster and more
reliable than DRAM but has a smaller capacity and is more
expensive, so it is mainly used as cache memory.
|
SRAM (Static
Random Access Memory) |
DRAM (Dynamic
Random Access Memory) |
|
SRAM is a type of
RAM that stores data without the need for frequent refreshing. |
DRAM is a type of
RAM that stores data temporarily and needs continuous refreshing. |
|
Very fast and more
expensive |
Slower than SRAM
and less expensive |
|
Smaller storage
capacity |
Larger storage
capacity |
|
Consumes less power
and more reliable |
Consumes more power
due to refreshing and less reliable compared to SRAM |
Types of ROM:
1. PROM (Programmable Read Only Memory)
PROM is a type of ROM
that is programmed only once after manufacturing. Once data is written
into PROM, it cannot be changed or erased. It is used when permanent
data storage is required.
2. EPROM (Erasable Programmable Read Only
Memory)
EPROM is a type of ROM
that can be erased using ultraviolet (UV) light and reprogrammed. It
allows data to be modified, but the chip must be removed from the computer for
erasing.
3. EEPROM (Electrically Erasable
Programmable Read Only Memory)
EEPROM is a type of ROM
that can be erased and reprogrammed electrically without removing it
from the computer. It is more flexible and commonly used in modern systems.
|
PROM |
EPROM |
EEPROM |
|
Programmable Read Only Memory |
Erasable Programmable Read Only Memory |
Electrically Erasable Programmable Read Only Memory |
|
PROM is a type of ROM that can be programmed only once
after manufacturing. |
EPROM is a type of ROM that can be erased and
reprogrammed using ultraviolet light. |
EEPROM is a type of ROM that can be erased and
reprogrammed electrically. |
|
Programmed only once |
Can be programmed multiple times |
Can be programmed multiple times |
|
Cannot be erased |
Erased using UV (ultraviolet) light |
Erased using electrical signals |
|
Not reusable |
Reusable after erasing |
Highly reusable |
|
Not applicable |
Must be removed from the computer for erasing |
No need to remove from the computer |
1.5.5 Example of
secondary memory (Storage devices): Hard disk drive (HDD), Solid State Drive
(SDD), Optical Discs (CD/DVD), Flash Memory
Hard Disk Drive
(HDD)
A Hard Disk Drive
(HDD) is a secondary storage device used to store data, programs,
and files permanently in a computer system. It is a non-volatile memory,
so data is not lost when the power is switched off. HDD stores data on magnetic
disks and has a large storage capacity, making it suitable for
long-term data storage.
The speed of a hard disk is measured in Revolutions
Per Minute (RPM), which usually ranges
from 5400 to 7200 rpm in common computers.
SSD (Solid State Drive)
A Solid State Drive
(SSD) is a secondary storage device used to store data, programs,
and files permanently in a computer system. It is a non-volatile memory
and stores data using flash memory instead of magnetic disks. SSDs are faster,
quieter, and more reliable than hard disk drives.
SSDs are widely used in laptops, notebooks, and
ultrabooks for high performance.
|
HDD (Hard Disk Drive) |
SSD (Solid State Drive) |
|
HDD is a secondary storage device that stores data
using magnetic disks. |
SSD is a secondary storage device that stores data
using flash memory. |
|
Has moving parts like rotating disks |
Has no moving parts |
|
Slower data access and consumes more power |
Faster data access and consumes less power |
|
Less durable, produce noise, cheaper |
More durable, silent, more expensive |
Optical Storage Disc
An Optical Storage Disc is a secondary storage
device used to store data permanently using laser light
technology. Data is read and written on the disc with the help of a laser
beam. It is a non-volatile storage, so data is not lost when the
power is switched off.
Common examples include CDs
(Compact Discs), DVDs (Digital Versatile Discs), and Blu-ray Discs.
CD (Compact Disc)
A CD (Compact Disc) is an optical
storage disc used to store data permanently. It uses laser
technology to read and write data. A CD is a non-volatile storage device,
so the data stored on it is not lost when the power is switched off.
A CD (Compact Disc) is an optical
storage disc used to store data permanently. It uses laser
technology to read and write data. A CD is a non-volatile storage device,
so the data stored on it is not lost when the power is switched off.
A standard CD is 12 cm in diameter,
1 mm thick, and weighs about 18 g. The
storage capacity of CD is 700MB.
DVD (Digital Versatile Disc)
A DVD (Digital Versatile Disc)
is an optical storage disc used to store data permanently. It
uses laser technology to read and write data. A DVD has a larger
storage capacity than a CD, making it suitable for storing videos,
software, and large data files.
A DVD is an optical storage disc
developed in 1995 by Philips, Sony, Toshiba, and Panasonic. A DVD drive
is required to read and write data on DVDs.
Storage Capacities:
- Single Side, Single Layer: 4.7 GB
- Single Side, Double Layer: 8.5 GB
- Double Side, Single Layer: 9.4 GB
- Double Side, Double Layer: 17.08 GB
|
CD (Compact Disc) |
DVD (Digital Versatile Disc) |
|
Uses laser technology to read and
write data |
Uses advanced laser technology to
read and write data |
|
Stores about 700 MB of
data |
Stores 4.7 GB or more of
data |
|
Lower data density and Slower
data access speed |
Higher data density and Faster
data access speed |
|
Usually single layer |
Can be single-layer or
double-layer |
|
Used for music, small software,
and documents |
Used for movies, videos, large
software, and data |
|
Lower video quality and Older
technology |
Better video quality and More
advanced than CD |
Blu-ray Disc
A Blu-ray Disc is an
optical storage disc used to store large amounts of data permanently. It uses a
blue-violet laser, which allows it to store more data than CDs and DVDs. It is
commonly used for high-definition videos and large data storage.
Flash Memory
Flash memory is a type of non-volatile
memory used to store data permanently. It stores data in electronic
form and does not require power to retain data. Flash memory is widely
used in devices such as pen drives, memory cards, and solid state drives
(SSD).
Pen Drive
A pen drive is
a portable secondary storage device that uses flash memory to store
data permanently. It is a non-volatile memory, so data is not lost
when power is switched off. A pen drive connects to a computer through a USB
port and is used for storing and transferring data.
Cloud Storage
Cloud storage is a type of online storage
system that allows users to store data on remote servers accessed
through the internet instead of storing it on a local device. It enables
users to access, share, and manage data from anywhere using an internet
connection. Examples: Google Drive, Dropbox, Microsoft OneDrive, Amazon
S3
Comparison Between
HDD, SSD, and Flash Memory
|
HDD (Hard Disk
Drive) |
SSD (Solid State
Drive) |
Flash Memory |
|
HDD is a secondary
storage device that stores data using magnetic disks. |
SSD is a secondary
storage device that stores data using flash memory chips. |
Flash memory is a
type of non-volatile memory used to store data electronically. |
|
Magnetic storage
(rotating platters) |
Flash memory
(electronic chips) |
Flash memory
(electronic) |
|
Has moving parts |
No moving parts |
No moving parts |
|
Slower data access
speed |
Very fast data
access speed |
Faster than HDD but
slower than SSD |
|
Less durable due to
moving parts |
More durable and
shock-resistant |
Highly durable |
|
Consumes more power |
Consumes less power |
Consumes very
little power |
|
Not portable |
Less portable |
Highly portable |
|
Used in traditional
desktop computers |
Used in modern
laptops and high-speed systems |
Used in pen drives,
memory cards, USB devices |
1.5.6 Function and
characteristics of each type of memory
|
Type of Memory |
Function |
Characteristics |
|
Primary Memory |
Stores data and
instructions currently required by the CPU for processing. |
• Directly accessed
by CPU • Fast in speed • Limited storage
capacity • Mostly volatile |
|
RAM (Random
Access Memory) |
Temporarily stores
data and instructions during execution of programs. |
• Volatile memory • Data lost when
power is off • Fast access speed
• Used during
processing |
|
ROM (Read Only
Memory) |
Stores instructions
needed to start the computer and load the operating system. |
• Non-volatile
memory • Permanent storage
• Mostly read-only • Stores firmware
(BIOS) |
|
Cache Memory |
Stores frequently
used data and instructions to improve CPU performance. |
• Very fast memory • Located between
CPU and RAM • Small capacity • Expensive |
|
Register |
Stores data and
instructions temporarily inside the CPU during processing. |
• Smallest and
fastest memory • Located inside
CPU • Very limited
capacity |
|
Secondary Memory |
Stores data and
programs permanently for future use. |
• Non-volatile
memory • Large storage
capacity • Slower than
primary memory • Not directly
accessed by CPU |
1. Memory in a computer is used to
A. Control hardware B.
✓
Store data, instructions, and results
C. Perform calculations D.
Display output
2. The smallest unit of memory is
A. Byte B. Nibble C. ✓ Bit D. Word
3. A group of 4 bits is called
A. Byte B. ✓ Nibble C. Word D.
Register
4. A byte consists of
A. 4 bits B. 6 bits C. ✓ 8 bits D. 16 bits
5. 1 KB is equal to
A. 1000 bytes B. 512 bytes C. ✓
1024 bytes D. 2048 bytes
6. Which memory is directly
accessed by the CPU?
A. Secondary memory B. Optical
memory C. ✓ Primary memory D. Flash memory
7. Which memory loses data when
power is switched off?
A. ROM B. HDD C. SSD D. ✓
RAM
8. Which of the following is
non-volatile memory?
A. RAM B. Cache C. ✓ ROM D. Register
9. BIOS is stored in
A. RAM B. Cache C. ✓ ROM D. Register
10. Cache memory is used to
A. Store files permanently B.
Increase storage capacity
C. ✓
Speed up CPU processing D. Backup
data
11. Registers are
A. Secondary storage devices B.
✓
Located inside CPU
C. Slower than RAM D.
Used for permanent storage
12. Which memory has the fastest
access speed?
A. RAM B. Cache C. ✓ Register D. SSD
13. Which memory is mostly
read-only?
A. RAM B. ✓ ROM C. Cache D.
Register
14. Firmware refers to programs
stored in
A. RAM B. HDD C. ✓ ROM D. Cache
15. Which memory is volatile?
A. ROM B. HDD C. SSD D. ✓ RAM
16. DRAM stands for
A. Direct RAM B. ✓ Dynamic Random Access Memory
C. Digital RAM D.
Dual RAM
17. Which RAM needs refreshing?
A. SRAM B. ✓ DRAM C. ROM D.
Cache
18. Which RAM is faster?
A. DRAM B. ✓ SRAM C. ROM D.
Flash
19. PROM can be programmed
A. Multiple times B. ✓ Only once C. After UV erase D. Electrically
20. EPROM is erased using
A. Electrical signals B. Heat C. ✓ UV light D. Magnet
21. EEPROM is erased using
A. UV light B. Heat C. ✓ Electrical signals D. Magnet
22. Which memory is permanent?
A. RAM B. Cache C. Register D. ✓ ROM
23. Which is secondary memory?
A. Cache B. Register C. RAM D. ✓
Hard disk
24. HDD stores data using
A. Laser B. Flash
memory C. ✓ Magnetic disks D. Electric charge
25. HDD speed is measured in
A. Mbps B. GHz C. ✓ RPM D. ns
26. SSD stores data using
A. Magnetic disks B.
Laser C. ✓ Flash memory D. Registers
27. Which storage has no moving
parts?
A. HDD B. ✓ SSD C. CD D.
DVD
28. Optical discs use
A. Magnetism B. Electricity C. ✓ Laser technology D. Heat
29. Standard CD storage capacity is
A. 4.7 GB B. 8.5 GB C. ✓ 700 MB D. 1 TB
30. Which memory helps reduce CPU
access time?
A. RAM B. HDD C. ✓ Cache D. ROM
31. Data currently being processed
is stored in
A. ROM B. HDD C. ✓ RAM D. CD
32. Booting instructions are stored
in
A. RAM B. ✓ ROM C. Cache D.
HDD
33. Which memory is fastest but
smallest?
A. RAM B. Cache C. ✓ Register D. SSD
34. Which is NOT primary memory?
A. RAM B. Cache C. Register D. ✓ HDD
35. Which device is best for
portability?
A. HDD B. SSD C. ✓ Pen drive D. DVD
36. A laptop boots faster mainly
due to
A. RAM size B. ✓ SSD C. CD drive D.
Cache size
37. Which memory retains data
without power?
A. RAM B. Cache C. ✓ ROM D. Register
38. Which storage is used for HD
movies?
A. CD B. DVD C. ✓ Blu-ray D. Pen drive
39. Which memory is slower than
RAM?
A. Cache B. Register C. ✓ ROM D. SRAM
40. Which storage is cloud-based?
A. HDD B. SSD C. Pen drive D. ✓
Google Drive
41. Which memory consumes more
power due to refreshing?
A. SRAM B. ✓ DRAM C. ROM D.
Cache
42. Which is more durable?
A. HDD B. ✓ SSD C. CD D.
DVD
43. Which memory is used during
execution of programs?
A. ROM B. HDD C. ✓ RAM D. CD
44. Which memory is inside CPU?
A. RAM B. Cache C. ✓ Register D. HDD
45. Which optical disc has highest
capacity?
A. CD B. DVD C. ✓ Blu-ray D. Pen drive
46. Which memory is erased using UV
light?
A. PROM B. ✓ EPROM C. EEPROM D.
ROM
47. Which memory does not need
refreshing?
A. DRAM B. ✓ SRAM C. RAM D.
Cache
48. Which is correct order of speed
(fast → slow)?
A. RAM → Cache → Register B.
HDD → RAM → Cache
C. ✓
Register → Cache → RAM D.
Cache → Register → RAM
49. Which storage is best for
long-term backup?
A. RAM B. Cache C. ✓ HDD D. Register
50. Which memory is closest to CPU?
A. RAM B. Cache C. ✓ Register D. SSD
51. Which is true about SSD?
A. Uses magnetic disks B.
Has moving parts
C. ✓
Faster and silent D. Needs RPM
52. Which storage is accessed via
internet?
A. HDD B. SSD C. ✓ Cloud storage D. CD
53. Which memory is used only
during startup?
A. RAM B. ✓ ROM C. Cache D.
HDD
54. Which memory stores OS files
permanently?
A. RAM B. ✓ HDD / SSD C. Cache D.
Register
55. Which memory type balances
speed and cost best?
A. Register B. Cache C. ✓ RAM D. SSD
1.
(A1) Why is RAM called volatile
memory? Explain with a suitable example.
2.
(A1) How does cache memory improve the
performance of the CPU?
3.
Differentiate
between SRAM and DRAM based on working principle and usage.
4.
(A1) Why is ROM essential for booting a
computer system?
5.
(A1) Explain the role of cache memory
between CPU and RAM.
6.
(A1) A system crashes suddenly. Which
type of memory data will be lost and why?
7.
(A1) Define computer memory.
Explain its functions and importance in a computer system.
8.
(A1) Explain primary memory.
Describe its types with suitable examples.
9.
Define
secondary memory. Explain different types of secondary storage devices
with examples.
10. (A1) Explain RAM and ROM in
detail. Compare them.
11. (A1) Explain the types of RAM.
Describe SRAM and DRAM with differences.
12. Explain ROM and its types: PROM,
EPROM, EEPROM.
13. Explain Hard Disk Drive (HDD)
and Solid State Drive (SSD). Compare them.
14. Explain optical storage devices:
CD, DVD, Blu-ray Disc with capacities.
15. (A1) Compare Primary memory and
Secondary memory.
