Chapter 1

Part A: Computer systems and data

Overview of computing systems

Last updated November 20264 sectionsabout 7 min read

Key takeaways

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.

This opening chapter fixes the vocabulary the rest of CISSE Foundation builds on: what a computer system actually is, the physical parts that make it up, the instructions that drive those parts, and how the two sides depend on each other.

The computer and its characteristics

A computer is an electronic device that accepts data as input, processes it under the control of a stored set of instructions (a program), and produces output, while retaining the ability to store data and instructions for later use. A computer system is the whole working combination: hardware, software, data, and the people (users, operators, programmers) who direct it.

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.

Hardware

Hardware is every physical, touchable component of a computer system, organised around one central processing loop: data enters through input, is manipulated by the processor, and leaves through output, with memory holding both data and instructions at every stage.

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.

Software

Software is the set of instructions (programs) that tells hardware what to do. Every computer needs software in two broad categories:

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.

How hardware and software interact

Hardware and software are interdependent: hardware without software is inert, it has no instructions to execute, and software without hardware has nothing to run on. The operating system is the bridge between the two, translating a user's or an application's requests into the low-level operations the CPU, memory and peripherals actually understand, while firmware (ROM-resident software such as the BIOS/UEFI) is itself the first layer that lets hardware boot and locate an operating system to hand control to.

Exam tip

A recurring CISSE Foundation question pattern is "classify the following as hardware, system software, or application software" against a mixed list (RAM, MS Word, antivirus, printer driver, hard disk). Anchor your answer to the hardware and software category lists rather than guessing from the item's name alone.

Self-check

(a) Classify each of the following as hardware, system software, or application software: RAM, MS Word, a printer driver, and antivirus software. (4 marks)

(b) Distinguish between RAM and ROM, and explain why ROM is described as non-volatile. (4 marks)

(c) State the five defining characteristics of a computer, and explain what 'garbage in, garbage out' means in relation to accuracy. (5 marks)

(d) Explain the relationship between hardware and software, and the specific role firmware plays in letting a computer boot at all. (4 marks)

(e) Distinguish between the ALU and the Control Unit as parts of the CPU. (3 marks)

Show worked answer

(a) RAM is hardware, a physical, touchable memory component. MS Word is application software, performing a specific task for the end user. A printer driver is system software, letting the operating system communicate with a specific hardware device. Antivirus software is utility software, a supporting category that keeps the system running well rather than doing user work directly. (4 marks)

(b) RAM (Random Access Memory) is volatile, holding the programs and data currently running, and its contents are lost when power is removed. ROM (Read Only Memory) is non-volatile, holding firmware such as the BIOS/UEFI that starts the machine. ROM is described as non-volatile because it retains its stored instructions even without power, essential since the computer needs those instructions to begin operating before any power-dependent memory has even been initialised. (4 marks)

(c) Speed, accuracy, diligence, storage, and versatility. 'Garbage in, garbage out' means a computer produces error-free results only if the input data and instructions themselves are correct, the computer's accuracy is a property of correctly executing what it is given, not a guarantee that the output is meaningful if the input itself was flawed. (5 marks)

(d) Hardware and software are interdependent, hardware without software is inert, it has no instructions to execute, and software without hardware has nothing to run on. Firmware, ROM-resident software such as the BIOS/UEFI, is the specific role that lets hardware boot and locate an operating system to hand control to, it is the first layer of software that runs, before any operating system has even loaded, bridging the gap between powering on the hardware and having a full software environment available. (4 marks)

(e) The Arithmetic and Logic Unit (ALU) performs calculations and logical comparisons. The Control Unit (CU) fetches, decodes and directs the execution of each instruction in turn, coordinating the CPU's overall operation rather than performing the calculations itself. (3 marks)