ZIMSEC O-Level Computer Science (4021)

Hardware and Software: notes

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Hardware: the parts you can touch

Input devices send data into the computer: keyboard, mouse, scanner, microphone, webcam, barcode reader, touch screen.
Output devices show or send results out: monitor, printer, speakers, projector.
Storage devices keep data when the power is off: hard disk drive (HDD), solid state drive (SSD), USB flash drive, memory card, optical disc (CD, DVD).
Processing happens in the CPU (central processing unit). It fetches an instruction from memory, decodes it, then executes it. This is the fetch-decode-execute cycle.

RAM (random access memory) holds the programs and data in use right now. It is volatile: switch off and it is empty.
ROM (read only memory) holds the start-up instructions (BIOS). It is non-volatile: it keeps its contents with no power.
Main memory is fast but small. Backing storage (HDD, SSD) is slower but much bigger.

System software runs the computer itself: the operating system (Windows, Linux, Android), utility programs (antivirus, disk defragmenter, backup) and device drivers.
Application software does a job for the user: word processor, spreadsheet, web browser, accounting package.
An operating system manages memory, files, users, security, and input and output devices, and gives the user an interface (GUI or command line).

Hardware maintenance: keep machines dust free, use a UPS (uninterruptible power supply) against power cuts, replace worn parts.
Software maintenance: install updates and patches, keep antivirus current, remove programs you no longer use.

Gotcha: a touch screen is both an input and an output device. RAM loses its contents when power goes; ROM does not.