Primary and Secondary Memory
Primary and Secondary Memory are two main types of computer memory. Primary memory is the computer’s main memory, used to store data and instructions while the computer is working.
It is fast but limited in size. Secondary memory, on the other hand, is used for permanent storage of data and programs. It is larger in capacity but slower than primary memory. Both types of memory are essential for the smooth functioning of a computer system.
1. Primary Memory
- Also called main memory or internal memory.
- It is the working memory of the computer.
- Stores data and instructions temporarily while the computer is in use.
- The CPU can directly access this memory.
Types of Primary Memory
a) RAM (Random Access Memory)
- Volatile memory → data is lost when power is turned off.
- Stores data and instructions that the CPU is currently processing.
- Two main types:
- SRAM (Static RAM) – faster and more expensive.
- DRAM (Dynamic RAM) – slower and cheaper.
Example:
When you open a program like MS Word, it loads from hard disk into RAM.
b) ROM (Read Only Memory)
- Non-volatile memory → data is permanent, even when power is off.
- Stores important instructions needed to start the computer (booting).
- Examples of ROM types:
- PROM (Programmable ROM) – can be written once.
- EPROM (Erasable Programmable ROM) – can be erased using UV light.
- EEPROM (Electrically Erasable PROM) – can be erased electronically.
c) Cache Memory
- A very high-speed memory located between CPU and RAM.
- Stores frequently used instructions for faster processing.
Advantages of Primary Memory
- Very fast access by the CPU.
- Essential for running programs.
Disadvantages of Primary Memory
- Limited storage capacity.
- Expensive compared to secondary memory.
- (RAM) loses data when power is off.
2. Secondary Memory
- Also called external memory or auxiliary storage.
- Used for permanent storage of data and programs.
- CPU cannot directly access it; data must first be loaded into primary memory.
Examples of Secondary Memory
- Hard Disk Drive (HDD)
- Solid State Drive (SSD)
- CDs / DVDs
- USB Flash Drives / Pen Drives
- Memory Cards
- Magnetic Tapes (older systems)
Characteristics of Secondary Memory
- Non-volatile → Data remains even after power is off.
- Large capacity → Can store terabytes of data.
- Slower than primary memory.
Advantages of Secondary Memory
- Low cost per unit of storage.
- Permanent data storage.
- Large capacity to store programs, files, videos, etc.
Disadvantages of Secondary Memory
- Slower access compared to primary memory.
- Requires primary memory for processing.
Difference between Primary and Secondary Memory
Feature | Primary Memory | Secondary Memory |
---|---|---|
Nature | Temporary (except ROM) | Permanent |
Speed | Very fast | Slower |
Cost | Expensive | Cheaper |
Capacity | Smaller (GBs) | Larger (GBs–TBs) |
Volatility | RAM is volatile | Non-volatile |
Examples | RAM, ROM, Cache | Hard Disk, SSD, USB, CD, DVD |
Quick Recap for Students
- Primary Memory: CPU’s working area → fast, temporary (RAM) or permanent (ROM).
- Secondary Memory: For permanent storage → hard disks, SSDs, USBs, CDs.
- Key Point: CPU works with primary memory first; secondary memory is used for long-term storage.
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