Know and understand characteristics of ROM and RAM

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Cambridge IGCSE ICT 0417 – Types and Components of Computer Systems

1. Types and Components of Computer Systems

Objective: Know and understand characteristics of ROM and RAM

In this section we explore two fundamental types of computer memory: Read‑Only Memory (ROM) and Random‑Access Memory (RAM). Understanding their characteristics is essential for grasping how computers store and retrieve data.

1.1 Read‑Only Memory (ROM)

ROM is non‑volatile memory that retains its contents even when the power is turned off. It is primarily used to store firmware and system instructions that must not be altered during normal operation.

  • Volatility: Non‑volatile – data persists without power.
  • Writeability: Typically write‑once or read‑only; some types can be rewritten under special conditions.
  • Typical Use Cases: BIOS/UEFI firmware, embedded system boot code, device drivers.
  • Speed: Generally slower to access than RAM.
  • Capacity: Usually smaller than RAM; ranges from a few kilobytes to several megabytes.
  • Examples: Mask ROM, PROM, EPROM, EEPROM, Flash ROM.

1.2 Random‑Access Memory (RAM)

RAM is volatile memory that is used for temporary storage of data and program instructions while a computer is running. It allows fast read and write operations.

  • Volatility: Volatile – data is lost when power is removed.
  • Writeability: Read/write; data can be modified at any time.
  • Typical Use Cases: Operating system memory, application data, cache, temporary buffers.
  • Speed: Very fast access times, typically measured in nanoseconds.
  • Capacity: Larger than ROM; ranges from a few gigabytes to tens of gigabytes in modern systems.
  • Types: Dynamic RAM (DRAM), Static RAM (SRAM), Synchronous DRAM (SDRAM).

1.3 Comparison of ROM and RAM

Feature ROM RAM
Volatility Non‑volatile Volatile
Writeability Write‑once or limited rewrite Read/write at any time
Primary Purpose Store firmware and permanent data Store temporary working data
Speed Slower access Fast access
Capacity Low to moderate (KB–MB) High (GB–TB)
Typical Example BIOS firmware System memory (e.g., 8 GB)

1.4 Key Takeaways

  • ROM holds essential instructions that must survive power cycles; it is not meant for frequent updates.
  • RAM provides the working space for the CPU, enabling rapid data manipulation during program execution.
  • The combination of ROM and RAM allows a computer to boot, run applications, and maintain performance.

1.5 Suggested Diagram

Suggested diagram: A block diagram showing the computer system with ROM connected to the CPU for boot instructions, and RAM connected to the CPU for active data processing.

1.6 Quick Quiz

  1. Which type of memory retains data when the computer is powered off?
  2. What is the main reason RAM is considered volatile?
  3. Give two examples of ROM types.
  4. Why is RAM faster than ROM?

Answers:

  • ROM
  • Because its contents are stored in capacitors that discharge when power is removed.
  • Mask ROM, EEPROM, Flash ROM, etc.
  • RAM uses dynamic or static circuits that allow rapid read/write operations, whereas ROM is typically fabricated with slower, non‑volatile storage mechanisms.