Know and understand differences between ROM and RAM

Types and Components of Computer Systems

Objective

Know and understand the differences between ROM (Read‑Only Memory) and RAM (Random‑Access Memory).

Key Concepts

• Memory is a fundamental component of any computer system. It stores data and instructions that the CPU needs to process.
• Memory can be broadly classified into two categories:
  • Primary (or main) memory – directly accessed by the CPU.
  • Secondary (or auxiliary) memory – used for long‑term storage.
• Within primary memory, the two most important types are ROM and RAM.

ROM – Read‑Only Memory

ROM is a non‑volatile memory that retains its contents even when the power is switched off. It is used to store firmware – the essential programs that start the computer and perform basic hardware control.

RAM – Random‑Access Memory

RAM is a volatile memory that loses its data when power is removed. It provides the workspace for the CPU to read and write data quickly while programs are running.

Comparison of ROM and RAM

Feature	ROM	RAM
Volatility	Non‑volatile – retains data without power	Volatile – data lost when power is removed
Purpose	Stores firmware, boot instructions, and permanent system software	Stores temporary data and program instructions while the computer is operating
Read/Write Capability	Primarily read‑only; writing is rare and usually done only by manufacturers or during firmware updates	Read and write operations are frequent and rapid
Speed	Slower than RAM (access times measured in microseconds)	Very fast (access times measured in nanoseconds)
Typical Capacity	Usually a few megabytes (e.g., BIOS chip 2–16 MB)	Typically several gigabytes (e.g., 4 GB, 8 GB, 16 GB, …)
Location on Motherboard	Integrated chips (e.g., BIOS/UEFI chip) or separate ROM modules	DIMM or SODIMM slots for RAM modules
Examples	BIOS/UEFI firmware, embedded system firmware, read‑only lookup tables	DDR4, DDR5 memory modules, video RAM (VRAM) on graphics cards

Why Both Types Are Needed

1. Boot Process: When the computer is switched on, the CPU fetches the initial instructions from ROM to start the system.
2. Program Execution: Once the operating system is loaded, RAM provides the fast, temporary workspace required for running applications.
3. Data Preservation: ROM ensures essential system software is always available, while RAM allows users to work with data that can be saved later to secondary storage (e.g., hard drive, SSD).

Summary

ROM and RAM serve distinct but complementary roles in a computer system. ROM provides permanent, non‑volatile storage for critical startup instructions, whereas RAM offers high‑speed, volatile memory for active processing. Understanding their differences helps learners appreciate how computers manage both permanent and temporary data.