Computer Hardware
This domain tests the physical organisation of a computer: CPU, memory hierarchy, buses, storage and peripherals.
The stored-program model
Hardware is the physical part of a computer. The CPU executes instructions in a fetch–decode–execute cycle: it fetches an instruction from memory using the program counter, decodes the operation, then executes it in the ALU or control unit, writing results to registers or memory. Registers are the fastest storage; cache (L1/L2/L3) is next; RAM is volatile main memory; SSD/HDD provide non-volatile secondary storage.
Buses, boards and peripherals
A bus carries data, addresses and control signals. The motherboard connects CPU, RAM slots, expansion slots and controllers. Input devices send data in; output devices present results. Ports and interfaces such as USB, HDMI and Ethernet follow standards that determine speed and compatibility.
Worked example
A system has a 12-bit address bus and 8-bit words. Addressable locations = 2^12 = 4096. With one byte per location, memory capacity = 4096 bytes = 4 KB. Doubling the address bus to 13 bits doubles locations to 8192 and capacity to 8 KB; adding data-bus width instead changes word size, not the number of addresses.
Traps that cost marks
- Calling RAM non-volatile; RAM loses contents on power-off.
- Assuming a higher clock speed always means a faster CPU; cores, cache and instruction mix matter.
- Confusing storage capacity with memory capacity.
- Treating a device driver as hardware rather than software.
Key hardware distinctions
ROM holds firmware such as the boot loader; RAM holds running programs and data. SSD has no moving parts, while HDD uses magnetic platters. A GPU accelerates parallel graphics or general compute but does not replace the CPU.