Computer Systems: Hardware, Software and Data Representation
Domain 2 - Computer systems: hardware, software and data representation
Tests von Neumann architecture, CPU/memory/storage, system vs application software, and how text, images and sound are encoded.
Core rules
- CPU fetch–decode–execute; registers include PC, MAR, MDR, CIR and accumulator; ALU, control unit, clock speed, cores and cache affect performance.
- Memory hierarchy: registers → cache → RAM → SSD/HDD; RAM is volatile, ROM is non-volatile.
- System software manages hardware (OS, utilities, drivers); application software serves user tasks.
- Data are bits; 8 bits = 1 byte. Decimal prefixes differ from binary: 1 KiB = 1024 B.
- Text: ASCII uses 7-bit codes; Unicode covers multilingual text. Images: resolution × colour depth. Audio: sampling rate × bit depth × channels × time.
Worked example
Estimate an uncompressed 800 × 600 image at 24-bit colour. Pixels = 800 × 600 = 480,000. Bits = 480,000 × 24 = 11,520,000 bits. Bytes = 11,520,000 / 8 = 1,440,000 B. In MiB = 1,440,000 / 1,048,576 ≈ 1.37 MiB. Reasoning: multiply pixel count by bits per pixel, divide by 8 for bytes, then by 1,024² for MiB. Compression reduces this, but lossy JPEG may discard detail.
Traps
Do not mix bits and bytes or MB and MiB. RAM is not long-term storage. “Software” is not only apps. Higher resolution alone does not guarantee better quality if colour depth or compression is poor.