CISSE Foundation Level
Computing Systems cheat sheet
Every chapter's key points, formulas and definitions on one page, for the last week before the exam. Each heading links to the chapter that explains it.
Overview of computing systems
- A computer accepts data as input, processes it under a stored program and produces output, while storing data and instructions for later use; a computer system is the whole combination of hardware, software, data and people.
- A computer's five characteristics are speed, accuracy, diligence, storage and versatility, and its accuracy holds only when the input and instructions are correct: garbage in, garbage out.
- The CPU is made up of the ALU, which calculates and compares, the Control Unit, which fetches, decodes and directs instructions, and registers, very small and very fast storage.
- RAM is volatile and holds the programs and data running now; ROM is non-volatile and holds firmware such as the BIOS/UEFI; secondary storage is larger and cheaper per byte but slower.
- System software manages the hardware and gives other software a platform, application software does the user's tasks, and utility software keeps the system running well.
Key terms
- Speed
- Processes millions of instructions per second, far beyond manual capability.
- Accuracy
- Produces error-free results provided the input data and instructions are themselves correct ("garbage in, garbage out").
- Diligence
- Performs the same operation repeatedly without fatigue or loss of consistency.
- Storage
- Retains vast quantities of data and instructions for later retrieval (the memory hierarchy, below).
- Versatility
- The same machine can process payroll, mark examinations, or route a phone call, depending only on which program is loaded.
- Central Processing Unit (CPU)
- The "brain" of the computer, made up of the Arithmetic and Logic Unit (ALU, performs calculations and comparisons), the Control Unit (CU, fetches, decodes and directs execution of instructions), and registers (very small, very fast storage holding the instruction and data currently in use).
- Primary memory
- Directly accessible to the CPU: RAM (Random Access Memory, volatile, holds the programs and data currently running) and ROM (Read Only Memory, non-volatile, holds firmware such as the BIOS/UEFI that starts the machine).
- Secondary storage
- Non-volatile storage for data and programs not currently in use: hard disk drives (HDD), solid-state drives (SSD), optical discs, and flash/USB drives; far larger and cheaper per byte than primary memory, but slower to access.
- Input devices
- Feed data and instructions into the system: keyboard, mouse, scanner, microphone, touchscreen, barcode/QR reader.
- Output devices
- Present processed results to the user: monitor, printer, speaker, projector.
- Motherboard
- The main circuit board that physically connects and lets the CPU, memory, storage and peripherals communicate, via buses (data, address, control) and expansion slots/ports.
- System software
- Manages the hardware itself and provides the platform other software runs on: the operating system (e.g. Windows, Linux, macOS, Android), device drivers, and utility programs.
- Application software
- Performs specific tasks for the end user: word processors, spreadsheets, accounting packages, browsers, and custom business systems (the kind of solution covered in the chapter on developing information systems).
- Utility software
- A supporting category, often bundled with the operating system, that keeps the system running well rather than doing user work directly: antivirus software, disk defragmenters/cleanup tools, file compression tools, and backup utilities.
The rest of the sheet covers
- Data processing
- Computer networks
- Developing information systems
- Types of information systems
- Application areas of ICT
- The impact of ICT on society
- Elementary programming principles
- Exam technique and revision
- Glossary