Computer Memory

1. What is Computer Memory?

Computer memory is a physical device used to store data, instructions, and results temporarily or permanently.
It allows the computer to process information quickly and efficiently.

Why Memory is Required?

• To store program instructions
• To store input data
• To store intermediate results
• To store final output

Without memory, a computer cannot function.

?? 2. Memory Organization & Hierarchy

Computer memory is organized in a hierarchical manner based on:

• Speed
• Cost
• Storage capacity

Memory Hierarchy Order:

1. Register Memory (Fastest, Costliest)
2. Cache Memory
3. Primary Memory (RAM & ROM)
4. Secondary Memory (Slowest, Cheapest)

?? Faster memory = Higher cost & lower capacity

?? 3. Types of Computer Memory

Computer memory is mainly divided into:

1. Primary Memory
2. Secondary Memory
3. Cache Memory
4. Register Memory

?? 4. Primary Memory (Main Memory)

Primary memory is the memory that is directly accessed by the CPU.

Characteristics:

• High speed
• Limited storage
• Expensive
• Mostly volatile

Primary memory stores currently running programs and data.

?? 5. Types of Primary Memory

Primary memory is classified into:

1. RAM (Random Access Memory)
2. ROM (Read Only Memory)
3. Cache Memory

?? 6. RAM (Random Access Memory) 

RAM is a volatile memory used to store data and programs that are currently in use.

Key Features:

• Data lost when power OFF
• Fast read & write
• Supports multitasking
• Direct CPU access

How RAM Works:

• Programs load from storage to RAM
• CPU accesses RAM for execution
• More RAM = Better performance

?? 7. Types of RAM

(a) SRAM – Static RAM

• Very fast
• No refresh required
• Expensive
• Used as cache memory

(b) DRAM – Dynamic RAM

• Slower than SRAM
• Needs frequent refresh
• Cheap
• Used as main memory

(c) VRAM – Video RAM

• Dedicated graphics memory
• Used in GPUs
• Stores textures & frames

?? 8. SRAM vs DRAM (Important Theory)

?? 9. ROM (Read Only Memory) 

ROM is a non-volatile memory that stores permanent instructions needed to start a computer.

Key Features:

• Data retained after power OFF
• Mostly read-only
• Used in booting

?? 10. Types of ROM

(a) PROM

• Programmed once
• Cannot be changed

(b) EPROM

• Erased using UV light
• Reprogrammable

(c) EEPROM

• Electrically erasable
• Selective erase possible

(d) Flash ROM

• Faster version of EEPROM
• Used in USB, SSD, memory cards

?? 11. Cache Memory

Cache memory is a small, high-speed memory placed between CPU and RAM.

Purpose:

• Reduce access time
• Increase CPU speed
• Store frequently used data

?? 12. Levels of Cache Memory

Cache memory is divided into three levels:

L1 Cache

• Fastest
• Smallest
• Inside CPU core

L2 Cache

• Slower than L1
• Larger size

L3 Cache

• Largest
• Shared among cores

?? 13. Register Memory

Register memory is the fastest memory located inside the CPU.

Characteristics:

• Very small
• Extremely fast
• Stores instructions & addresses

Types of Registers:

• Program Counter (PC)
• Instruction Register (IR)
• Memory Address Register (MAR)
• Memory Data Register (MDR)

?? 14. Secondary Memory

Secondary memory stores data permanently and is not directly accessed by CPU.

Characteristics:

• Non-volatile
• Large capacity
• Slow but cheap

?? 15. Types of Secondary Memory

Magnetic Storage:

• Hard Disk Drive (HDD)
• Magnetic Tape

Optical Storage:

• CD
• DVD
• Blu-ray Disc

Flash Storage:

• SSD
• Pen Drive
• Memory Cards

Cloud Storage:

• Google Drive
• OneDrive
• Dropbox

?? 16. RAM vs ROM (Theory Comparison)

?? 17. Important Teaching Points

• Cache improves system speed
• RAM affects multitasking
• ROM stores firmware
• SSD is faster than HDD
• Memory hierarchy balances cost & speed