Computer Fundamentals and Hardware
This domain of the PSEB Matric Computer Science paper tests the block diagram of a computer, input and output devices, CPU, memory hierarchy, storage units, and hardware versus software. Questions often ask you to classify a device or convert storage units.
Core rules
- A computer follows input–process–output. The CPU contains the ALU (arithmetic logic unit) and CU (control unit); registers sit inside the CPU.
- Primary memory is directly accessed by the CPU: RAM is volatile and holds running programs; ROM is non-volatile and stores firmware such as BIOS.
- Secondary storage (hard disk, SSD, pen drive, DVD) is non-volatile and slower; cache is small, fast memory between CPU and RAM.
- Exam convention: 1 byte = 8 bits; 1 KB = 1024 bytes; 1 MB = 1024 KB; 1 GB = 1024 MB; 1 TB = 1024 GB.
- Input devices send data in (keyboard, mouse, scanner, barcode reader, microphone); output devices send results out (monitor, printer, plotter, speaker). A touchscreen is both.
Worked example
A 16 GB pen drive stores photos of 4 MB each. Convert: 16 GB = 16 × 1024 MB = 16,384 MB. Divide by 4 MB: 16,384 ÷ 4 = 4,096 photos. Reasoning: the exam uses binary multiples (1024), not decimal (1000), and the units must match before dividing. If the question said 16,000 MB, you would divide 16,000 by 4 instead.
Traps that cost marks
- Calling RAM non-volatile, or saying ROM is wiped on shutdown.
- Mixing MB (megabyte) with Mb (megabit): 1 MB = 8 Mb.
- Treating the CPU as the whole system box; the CPU is the processor chip.
- Forgetting that a device can be both input and output.
- Writing 1000 instead of 1024 in storage conversions.