Cambridge IGCSE ICT 0417 – Types and Components of Computer Systems
Topic: Types and Components of Computer Systems
Objective
Know and understand internal memory, including Random Access Memory (RAM) and Read‑Only Memory (ROM).
1. Overview of Internal Memory
Internal memory, also called primary or main memory, is the part of a computer that stores data and instructions that the CPU can access directly. It is essential for the speed and performance of the system.
Volatile memory – loses its contents when power is removed (e.g., RAM).
Non‑volatile memory – retains data without power (e.g., ROM, flash memory).
2. Random Access Memory (RAM)
RAM is the working memory of a computer. It holds data and program instructions that are currently being used.
Read and write operations are possible.
Provides fast access – typical access time is a few nanoseconds.
Capacity is expressed in megabytes (MB) or gigabytes (GB).
Types of RAM:
Dynamic RAM (DRAM) – needs periodic refreshing.
Static RAM (SRAM) – faster, does not need refreshing, used for cache.
When the computer is switched off, all data stored in RAM is lost.
3. Read‑Only Memory (ROM)
ROM stores permanent instructions that are required for the computer to start and operate.
Data is written during manufacturing and cannot be easily altered.
Provides the firmware, such as the BIOS or UEFI, which performs the Power‑On Self‑Test (POST) and loads the operating system.
Types of ROM:
Masked ROM – programmed during chip fabrication.
Programmable ROM (PROM) – can be written once after manufacturing.
Erasable PROM (EPROM) – can be erased with U \cdot light and re‑programmed.
Electrically Erasable PROM (EEPROM) – can be erased and re‑programmed electrically.
Non‑volatile – retains its contents even when power is removed.
4. Comparison of RAM and ROM
Feature
RAM
ROM
Purpose
Temporary storage for active data and programs
Permanent storage for system firmware and boot instructions
Volatility
Volatile (data lost when power is off)
Non‑volatile (data retained without power)
Read/Write Capability
Both read and write
Typically read‑only; some types can be re‑programmed
Speed
Very fast (nanoseconds)
Slower than RAM
Typical Capacity
4 GB – 64 GB (or more) for modern PCs
Few kilobytes to several megabytes
Examples
DDR4, DDR5 modules
BIOS chip, firmware in embedded devices
5. How RAM and ROM Work Together
When a computer is powered on, the CPU reads the boot instructions from ROM. These instructions locate and load the operating system into RAM, where it can be accessed quickly while the system runs.
During operation, the CPU continuously reads from and writes to RAM, while ROM remains unchanged, providing a stable reference for essential system functions.
Suggested diagram: Block diagram showing the CPU connected to both RAM and ROM, illustrating the flow of data during the boot process and normal operation.
6. Quick Revision Questions
What is the main difference between volatile and non‑volatile memory?
Explain why RAM is considered “random access”.
List two types of ROM and describe how they can be re‑programmed.
Why is it important for the BIOS to be stored in ROM rather than RAM?
Match the following capacities with the correct memory type: