Computer Systems and Hardware
What the exam tests
This domain covers the physical and logical building blocks of a computer: CPU, main memory, secondary storage, input/output devices, motherboard, buses and performance measurement. Questions often ask you to classify a component, explain the fetch–decode–execute cycle, or compare technologies.
Core rules
- The CPU contains the control unit, arithmetic logic unit (ALU) and registers. Registers are fastest; cache is next; RAM is main memory; secondary storage is persistent.
- RAM is volatile and holds programs/data in use; ROM is non-volatile and holds firmware such as the bootstrap loader.
- Buses carry addresses, data and control signals. The width of the address bus limits addressable memory; data bus width affects word size.
- Solid-state drives have no moving parts, lower latency and better shock resistance than magnetic hard disks, but cost per gigabyte is usually higher.
Worked example
A CPU runs at 2 GHz and executes a program of 1,000,000,000 instructions with an average of 4 clock cycles per instruction. Time = instructions × CPI ÷ clock rate = 1×10^9 × 4 ÷ 2×10^9 = 2 seconds. Reasoning: clock rate alone does not determine speed; CPI and instruction count matter. A 3 GHz CPU with CPI 8 would take 2.67 seconds, so it is slower on this program.
Traps that cost marks
Do not treat GHz as a complete performance measure. Do not say RAM stores files permanently. Distinguish cache (small, fast, hardware-managed) from RAM. In storage questions, 1 TB is decimal for manufacturers but binary in many OS displays. Do not confuse input devices with output devices: a touchscreen is both.
Exam focus
Expect component-function matching, memory hierarchy ordering and simple performance calculations.