MEMORY & STORAGE
Memory is one of the most essential components of a computer. A computer cannot perform even simple tasks without memory. The performance of a computer mainly depends on the CPU and memory.
Computer memory is an internal storage medium used to store data, instructions, and information. It is broadly classified into two major types:
COMPUTER MEMORY
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┌────────────┴────────────┐
│ │
PRIMARY MEMORY SECONDARY MEMORY
(Main Memory) (Auxiliary Memory)
- Main Memory / Primary Memory
- Secondary Memory
1. PRIMARY MEMORY
Primary memory is the memory that the CPU or processor accesses directly or first. It stores the data, instructions, and programs that are currently being used or processed by the computer.
Primary memory is also known as:
- Main Memory
- Primary Storage
- Internal Memory
It is mainly divided into:
PRIMARY MEMORY
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┌─────────┴─────────┐
│ │
RAM ROM
(Volatile) (Non-Volatile)
- RAM – Random Access Memory
- ROM – Read Only Memory
RANDOM ACCESS MEMORY (RAM)
RAM is a volatile memory. This means that it does not store data or instructions permanently.
It is a read/write memory that temporarily stores data and instructions while the computer is operating.
Working of RAM
When a computer is switched on and a task is performed:
HARD DISK / STORAGE
│
▼
RAM
│
▼
CPU
│
▼
PROCESSING
The data and instructions required for processing are transferred from secondary storage to RAM. The CPU then accesses the data from RAM to perform the required tasks.
Important: When the computer is switched off, the data stored in RAM is lost.
Types of RAM
1. DRAM (Dynamic Random Access Memory)
- DRAM must be constantly refreshed to retain its contents.
- It is relatively economical.
- It is widely used as a type of main memory.
2. SRAM (Static Random Access Memory)
- SRAM is faster than DRAM.
- It does not require constant refreshing like DRAM.
- It requires more power.
- It is more expensive than DRAM.
3. SDRAM (Synchronous Dynamic Random Access Memory)
- SDRAM is a type of DRAM.
- It operates synchronously with the computer’s system clock.
- It can operate at much higher clock speeds than conventional DRAM.
READ ONLY MEMORY (ROM)
ROM is a non-volatile memory. This means that it retains its data and instructions even when the power supply is switched off.
ROM generally contains important instructions required for essential computer operations, including the boot process.
ROM
│
┌───────┼────────┐
│ │ │
PROM EPROM EEPROM
Types of ROM
1. PROM (Programmable Read Only Memory)
- PROM can be programmed by the user.
- Data can be written to it only once.
- Once programmed, the data cannot normally be erased or modified.
2. EPROM (Erasable Programmable Read Only Memory)
- EPROM can be erased and reprogrammed.
- The stored data can be erased using ultraviolet (UV) light.
- After erasing, the chip can be programmed again.
3. EEPROM (Electrically Erasable Programmable Read Only Memory)
- EEPROM can be erased and reprogrammed electrically.
- Unlike EPROM, it does not require ultraviolet light for erasing data.
OTHER TYPES OF MEMORY
1. REGISTER MEMORY
Register memory is the smallest and fastest memory in a computer.
It is located inside the CPU in the form of registers.
A register temporarily stores:
- Frequently used data
- Instructions
- Memory addresses
These can be accessed very quickly by the CPU.
CPU
│
REGISTERS
│
FASTEST MEMORY
2. CACHE MEMORY
Cache memory is small in size but faster than the main memory.
It stores frequently used data and instructions so that the CPU can access them quickly.
Working of Cache Memory
CPU
│
▼
CACHE MEMORY
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Data Found?
┌──┴──┐
YES NO
│ │
▼ ▼
Use Data Access RAM
If the CPU finds the required data or instructions in the cache memory, it does not need to access the slower primary memory.
Result: Cache memory helps improve the overall performance of the computer.
3. SEMI-VOLATILE MEMORY
Semi-volatile memory is a type of memory that retains data for a limited period after the power supply is removed.
However, the data is eventually lost.
It aims to provide some of the performance and durability benefits of volatile memory while also offering some advantages associated with non-volatile memory.
4. VIRTUAL MEMORY
Virtual memory is a memory-management system controlled by the operating system.
When a program requires memory, it requests memory from the operating system. The operating system then determines where the program’s data and instructions should be placed in physical memory.
Virtual memory allows a computer to handle programs that may require more memory than the available physical RAM.
5. PROTECTED MEMORY
Protected memory is a system in which each program is assigned a specific area of memory.
A program is not permitted to access the memory area assigned to another program without proper permission.
┌──────────────┐
│ PROGRAM A │
├──────────────┤
│ PROGRAM B │
├──────────────┤
│ OPERATING │
│ SYSTEM │
└──────────────┘
Protected memory improves:
- System reliability
- Computer security
- Program stability
2. SECONDARY MEMORY
Secondary memory refers to storage devices that are present inside or connected to a computer.
It is non-volatile, meaning that it permanently stores data even when the computer is switched off.
The CPU cannot directly access data stored in secondary memory. The data must first be transferred to primary memory, after which the CPU can access and process it.
SECONDARY MEMORY
(Hard Disk, SSD)
│
▼
PRIMARY MEMORY
(RAM)
│
▼
CPU
Secondary memory generally has a much larger storage capacity than primary memory.
TYPES OF SECONDARY STORAGE
There are three major types of secondary storage:
1. SOLID-STATE STORAGE
Examples include:
- USB Memory Sticks
- Solid-State Drives (SSDs)
- Flash Memory Devices
Solid-state storage stores data electronically in semiconductor chips.
It is generally faster than traditional hard disk drives because it does not contain moving mechanical parts.
2. OPTICAL STORAGE
Examples include:
- CD
- DVD
- Blu-ray Disc
Optical storage devices use a laser to read or write data on the surface of a disc.
The surface of an optical disc contains tracks with:
- Lands – Flat areas
- Pits – Hollow areas
LASER
│
▼
┌─────────────┐
│ OPTICAL DISC│
│ PITS/LANDS │
└─────────────┘
3. MAGNETIC STORAGE
Examples include:
- Hard Disk Drives
- Magnetic Tapes
- Floppy Disks
Magnetic storage devices use magnetic fields to store data on magnetic surfaces.
Each small section represents a bit:
- Magnetised section → Binary 1
- Demagnetised section → Binary 0
HARD DISK DRIVE
A hard disk drive (HDD) is a non-removable storage device containing magnetic disks or platters that rotate at high speeds.
Data is stored in segments of concentric circles on the platters.
A hard disk may rotate at speeds ranging from approximately 5,400 to 15,000 RPM, depending on the type of drive.
OPTICAL DISK
An optical disk is an electronic data storage medium that can be read and, in some cases, written using a low-powered laser beam.
Types of Optical Discs
CD-ROM
- Stands for Compact Disc Read-Only Memory.
- Data can only be read.
- Commonly used for distributing software and other information.
- Traditional standard capacity: approximately 640 MB.
CD-R
- Stands for Compact Disc Recordable.
- Also known as WORM – Write Once, Read Many.
- Data can be written once and read multiple times.
CD-RW
- Stands for Compact Disc Rewritable.
- Data can be erased and rewritten multiple times.
DVD
- Stands for Digital Versatile Disc.
- Similar to a CD but has a significantly larger storage capacity.
- A common single-layer DVD has a capacity of approximately 4.7 GB.
WORM
WORM stands for Write Once, Read Many.
It refers to a data storage system in which information, once written, cannot be modified.
FLOPPY DISK
A floppy disk consists of a thin, flexible magnetic disk enclosed in a square plastic casing.
Floppy disks were widely used for:
- Distributing software
- Transferring files
- Creating backup copies of data
A computer required a Floppy Disk Drive (FDD) to read and write data from a floppy disk.
MAGNETIC TAPE
Magnetic tape is a magnetic storage medium used for recording:
- Sound
- Pictures
- Computer data
It has traditionally been used for data storage and backup purposes.
FLASH MEMORY
Flash memory is a type of memory that retains data even when the power supply is removed.
Examples include:
- USB flash drives
- Memory cards
- Solid-state storage devices
PRIMARY MEMORY VS SECONDARY MEMORY
| Primary Memory | Secondary Memory |
| It includes volatile and non-volatile memory. | It is generally non-volatile. |
| Also known as internal or main memory. | Also known as auxiliary, backup, or additional memory. |
| Data can be accessed directly by the processing unit. | Data cannot be directly accessed by the processor. |
| Data is transferred to the CPU through primary memory. | Data must first be transferred to primary memory before the CPU can process it. |
| Stores data and information currently being used by the processing unit. | Stores large amounts of data and information for long-term use. |
| Generally has lower storage capacity. | Generally has much higher storage capacity. |
| Can be accessed through the data bus. | Accessed through I/O channels. |
| More expensive than secondary memory. | Less expensive than primary memory. |
MEMORY UNITS
A memory unit represents the amount of data that can be stored in a computer’s memory or storage device.
Storage capacity is commonly expressed in terms of bits and bytes.
BIT
│
▼
NIBBLE
│
▼
BYTE
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▼
KB → MB → GB → TB → PB → EB → ZB → YB
Units of Memory
| Unit | Description |
| Bit | A binary digit represented by 0 or 1. |
| Nibble | A group of 4 bits. |
| Byte | A group of 8 bits. It is commonly used to represent a character or data item. |
| Kilobyte (KB) | 1 KB = 1024 Bytes |
| Megabyte (MB) | 1 MB = 1024 KB |
| Gigabyte (GB) | 1 GB = 1024 MB |
| Terabyte (TB) | 1 TB = 1024 GB |
| Petabyte (PB) | 1 PB = 1024 TB |
| Exabyte (EB) | 1 EB = 1024 PB |
| Zettabyte (ZB) | 1 ZB = 1024 EB |
| Yottabyte (YB) | 1 YB = 1024 ZB |
1. Which of the following is a volatile memory?
A. ROM
B. RAM
C. CD-ROM
D. Hard Disk
Answer: B. RAM
2. RAM stands for:
A. Read Access Memory
B. Random Access Memory
C. Rapid Access Memory
D. Readable Access Memory
Answer: B. Random Access Memory
3. What happens to the data stored in RAM when the computer is switched off?
A. It is permanently stored
B. It is transferred to ROM
C. It is lost
D. It is transferred to the hard disk automatically
Answer: C. It is lost
4. Which of the following is a non-volatile memory?
A. RAM
B. Cache
C. ROM
D. Register
Answer: C. ROM
5. ROM stands for:
A. Random Only Memory
B. Read Only Memory
C. Read Open Memory
D. Rapid Operating Memory
Answer: B. Read Only Memory
6. Which memory stores instructions required during the booting process?
A. RAM
B. ROM
C. Cache
D. Register
Answer: B. ROM
7. Which type of memory is the fastest?
A. Hard Disk
B. RAM
C. Cache Memory
D. Optical Disk
Answer: C. Cache Memory
8. Which is the smallest and fastest memory in a computer?
A. RAM
B. ROM
C. Register
D. Hard Disk
Answer: C. Register
9. Which type of RAM needs to be refreshed periodically?
A. SRAM
B. DRAM
C. PROM
D. EEPROM
Answer: B. DRAM
10. Which type of RAM is faster?
A. DRAM
B. SRAM
C. PROM
D. EPROM
Answer: B. SRAM
11. SRAM stands for:
A. Static Random Access Memory
B. System Random Access Memory
C. Static Read Access Memory
D. System Readable Access Memory
Answer: A. Static Random Access Memory
12. DRAM stands for:
A. Dynamic Random Access Memory
B. Digital Random Access Memory
C. Dynamic Read Access Memory
D. Direct Random Access Memory
Answer: A. Dynamic Random Access Memory
13. Which memory can be programmed only once?
A. RAM
B. PROM
C. EPROM
D. EEPROM
Answer: B. PROM
14. Which memory can be erased using ultraviolet light?
A. PROM
B. EPROM
C. EEPROM
D. RAM
Answer: B. EPROM
15. Which memory can be electrically erased and reprogrammed?
A. PROM
B. EPROM
C. EEPROM
D. ROM
Answer: C. EEPROM
16. Cache memory is located between:
A. Keyboard and Mouse
B. CPU and Main Memory
C. Monitor and Printer
D. Hard Disk and Keyboard
Answer: B. CPU and Main Memory
17. The main purpose of cache memory is to:
A. Store data permanently
B. Increase processing speed
C. Store backup files
D. Print documents
Answer: B. Increase processing speed
18. Which of the following is primary memory?
A. RAM
B. Hard Disk
C. CD-ROM
D. Pen Drive
Answer: A. RAM
19. Which of the following is secondary storage?
A. RAM
B. ROM
C. Cache Memory
D. Hard Disk
Answer: D. Hard Disk
20. Which memory is directly accessible by the CPU?
A. Primary Memory
B. Secondary Memory
C. Optical Disk
D. Magnetic Tape
Answer: A. Primary Memory
21. Which of the following is a magnetic storage device?
A. Hard Disk
B. CD-ROM
C. DVD
D. Blu-ray Disc
Answer: A. Hard Disk
22. A hard disk stores data using:
A. Magnetic technology
B. Laser technology only
C. Sound waves
D. Light signals only
Answer: A. Magnetic technology
23. Which of the following is an optical storage device?
A. Hard Disk
B. CD-ROM
C. RAM
D. Pen Drive
Answer: B. CD-ROM
24. Optical disks are read and written using:
A. Magnetic fields
B. Laser beams
C. Radio waves
D. Electrical wires
Answer: B. Laser beams
25. CD-ROM stands for:
A. Compact Disc Read Only Memory
B. Computer Disc Random Operating Memory
C. Compact Data Read Only Machine
D. Computer Data Read Only Memory
Answer: A. Compact Disc Read Only Memory
26. Which of the following can be rewritten multiple times?
A. CD-ROM
B. CD-R
C. CD-RW
D. WORM
Answer: C. CD-RW
27. CD-R stands for:
A. Compact Disc-Recordable
B. Computer Disc-Readable
C. Compact Data-Read
D. Computer Data Recorder
Answer: A. Compact Disc-Recordable
28. Which storage device generally has greater capacity than a CD?
A. DVD
B. Floppy Disk
C. Magnetic Tape
D. RAM
Answer: A. DVD
29. DVD stands for:
A. Digital Video Device
B. Digital Versatile Disc
C. Direct Video Disc
D. Digital Visual Data
Answer: B. Digital Versatile Disc
30. Which of the following uses a laser to read and write data?
A. Optical Disk
B. RAM
C. Register
D. Magnetic Tape only
Answer: A. Optical Disk
31. A floppy disk is a:
A. Magnetic storage device
B. Optical storage device
C. Semiconductor memory
D. Primary memory
Answer: A. Magnetic storage device
32. The device used to read and write data on a floppy disk is called:
A. CD Drive
B. Floppy Disk Drive
C. Hard Disk Drive
D. Tape Drive
Answer: B. Floppy Disk Drive
33. A floppy disk is made up of:
A. A thin magnetic disk
B. A laser disc
C. Silicon chips only
D. Magnetic tape only
Answer: A. A thin magnetic disk
34. Which of the following is an older removable storage medium?
A. Floppy Disk
B. RAM
C. Cache
D. Register
Answer: A. Floppy Disk
35. Which type of memory retains data even when power is removed?
A. Volatile memory
B. Flash memory
C. Cache memory only
D. Register memory
Answer: B. Flash memory
36. A pen drive generally uses:
A. Flash memory
B. Vacuum tubes
C. Magnetic tape only
D. Cache memory
Answer: A. Flash memory
37. Which of the following is a solid-state storage device?
A. SSD
B. Floppy Disk
C. Magnetic Tape
D. CD-ROM
Answer: A. SSD
38. SSD stands for:
A. Solid State Drive
B. System Storage Device
C. Secure Storage Disk
D. Solid Storage Data
Answer: A. Solid State Drive
39. Compared with a traditional HDD, an SSD generally:
A. Has moving magnetic platters
B. Uses no moving parts
C. Uses floppy disks
D. Uses vacuum tubes
Answer: B. Uses no moving parts
40. Which of the following is commonly used for backup storage?
A. Secondary Memory
B. Register
C. Cache
D. ALU
Answer: A. Secondary Memory
41. The smallest unit of data in a computer is:
A. Byte
B. Bit
C. Nibble
D. Word
Answer: B. Bit
42. One byte is equal to:
A. 2 bits
B. 4 bits
C. 8 bits
D. 16 bits
Answer: C. 8 bits
43. One nibble is equal to:
A. 2 bits
B. 4 bits
C. 8 bits
D. 16 bits
Answer: B. 4 bits
44. 1 KB is generally equal to:
A. 100 Bytes
B. 512 Bytes
C. 1024 Bytes
D. 2048 Bytes
Answer: C. 1024 Bytes
45. 1 MB is equal to:
A. 1024 KB
B. 1024 GB
C. 100 KB
D. 1000 GB
Answer: A. 1024 KB
46. 1 GB is equal to:
A. 1024 KB
B. 1024 MB
C. 1024 TB
D. 100 MB
Answer: B. 1024 MB
47. Arrange the following in ascending order of storage capacity:
A. GB, MB, KB, TB
B. KB, MB, GB, TB
C. MB, KB, TB, GB
D. TB, GB, MB, KB
Answer: B. KB, MB, GB, TB
48. Which of the following memories is termed as the working memory of the computer?
(A) RAM
(B) ROM
(C) Cache
(D) None of the above
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