Components of a Computer System and Modes of Use
1.1.1 Types of hardware
1.1.2 Types of software
Candidates should be able to:
(a) define the terms hardware, software, input, storage and output device;
(b)describe the purpose of input devices, storage devices and output devices;
(c) define the different types of software: os, user interface, translator, utilities, programming languages & generic/common applications software;
(d) describe the hardware used to enable computers to communicate.
Types of Hardware: The internal components of a computer system are:
Processor- the part if the computer system that executes the programs; The processor is the heart of the computer system. The power of a processor is controlled by the clock speed and the complexity of the instructions it is able to execute. It executes the program that is stored in the memory. The processor has three main components: Control Unit, Arithmetic and Logic Unit (ALU) and Registers. The Control Unit controls the rest of the processor by generating appropriate control signals. The ALU preforms arithmetic operations and the Registers are a small number of read/write memory cells that operate at very high speed. When the computer is turned on it starts performing what is known as the fetch/execute cycle. The main memory will have coded program instructions and the purpose of fetch/executes cycle is to execute these instructions. To assist in this process one of the register is used exclusively to keep track of the memory address if the next instruction. This register is often called the Program Counter. The fetch/execute cycle consists of the followingsteps:
- The processor copies the contents of the program counter on the address bus and requests that the memory be read.
- The processor reads the data bus that now contains the instruction to be decoded and stores it in the instruction register.
- The processor executes the instruction and increments the program counter.
this manner the processor works its way through any program that is
stored in the main memory. The speed of the processor is controlled by
the speed of the clock. the width of the buses and the size and number
of the registers will affect the complexity of the instructions that
the processor can execute.
Memory- high-speed storage for programs and data; A computer's memory is normally organised into memory into memory locations. A memory location is a fixed amount of memory that has an address. The address is simply a number that can be used to allow immediate access to any memory location. When the processor wishes to access a memory location's address on the address bus and sends appropriate control signals via the control bus. If a memory location contains 8 binary digits (bits) it is known as a byte. If it contains more than 8 bits (typically 16, 32, 64 or 128 bits) it is known as a word.
- Read Only Memory: Some of the computer's memory is known as read only memory (or ROM). The contents of ROM cannot be changed by the processor. When the computer is turned off the contents of ROM are maintained so that it still has the same information when you turn the computer back on again. This type of memory is known as non-volatile. ROM is used for the following purposes: to store the bootstrap program that starts the computer; to store fixed data associate with the computer system; sometimes to store programs that remain in the computer at all times, for example a palmtop may have all its programs stored in ROM.
- Random Access Memory: All memory is random access in that it can be accessed randomly, but the name random access memory is given to the memory that can be written to. It should really be read/write memory. When the computer is switched off the contents of RAM are lost. For this reason RAM is known as volatile memory. RAM is used for the following purposes: to store programs that are being executed; to store data that are required for immediate use; as buffers for external storage devices.
- Cache Memory: Many computer system have special high special high-speed memory that is known as cache memory chip. It is used to speed up the execution of computer programs. The following may be stored in cache memory: program instructions that are executed many times; regularly used data; virtual memory page tables; pipelining (Pipelining is a hardware feature that speeds up the execution of program instructions.) Cache memory is faster then RAM and ROM but it is slower to access than a register.
Interfaces- to connect external device, called peripherals; In oder to connect external devices to the system, interfaces are required. An interface is able to communicate with the buses of the system and also with the external devices. The external devices will use different protocols from the rest of the computer system. the interface will provide the following features; the external device will normally operate at a much lower speed than the buses; the external devices may use a different voltage; the interface will provide electrical protection from faulty device. An interface will consist of; electron to connect to the system bus; electronics to connect to the cable that goes to the device; Data registers to hold the data being transferred; control register to allow commands to be passed to the device; control register to be passed to the interface and status register to provide information about the current state of the device.
Clock- to provide timing signals; The clock is a simple electronic device that produces a pulse of electricity at regular intervals. It is used to synchronise the computer system. The clock is normally connected to the processor that passes on synchronising signals through the contorl bus. Clock speed are usually measured in megahertz (MHz). 1 MHZ is 1 million clock signals every second.
Buses- to connect together all of the above into a computer system; A system bus is simply a number of wires that are used to connect devices together in such a way as to allow data or control information to pass from device to device. The system bus will normally consist of three buses: Data bus; Address bus and Control bus.
Types of Software:
Systems Software includes the operating system and all the utilities that enable the computer to function.
Applications Software includes programs that do real work for users, For example, word processors spreadsheets and database management systems fall under the category of applications software.
(a) define the terms hardware, software, input device, storage device and output device;
Computer hardware: The physical equipment used in a computer system.
Computer program: Another name for computer software, a series of commands or instructions that a computer can interpret and execute.
Software: Its Characteristics are: It is developed and engineered; doesn't wear-out; most software continues to be custom built. Most of the software on your computer comes in the form of programs. A program consists of "instructions" that tell the computer what to do
Past Questions for 2002
- Explain what is meant by the term generic applications software. 
- State an example of an application where it would not be appropriate to use generic applications software, giving a reason for your answer. 
- Distinguish between operating system software and applications software. 
- The person responsible for the computer system in a college buys an integrated applications package made up of generic software. 
Explain what is meant by
(i) integrated software,
(ii) an applications package,
(iii) generic software.
- State what is meant by
(i) operating system software;
(ii) applications software.
- Define the terms
(i) input device;
- (ii) output device.
- A supermarket has a number of point of sale (POS) terminals.
State two input devices and one output device that would be found at each POS terminal,
describing what they are used for. 
- State what is meant by 
(i) generic applications software,
- (ii) operating system software.
- Describe three features which an operating system would be expected to provide in a
single user computer system. 
- Explain the meaning of the terms
(i) input device,
(ii) output device. 
- A manufacturing process in a company is manually controlled. The company employs a systems analyst to plan the introduction of a computerized control system. Explain why generic applications software is not appropriate for controlling the production line. 
- Authors send books to a publishing company. At this stage books are text documents with any illustrations being added at the end of the publishing process. All copy editors are expected to have a stand-alone computer. Copy editors need to communicate with head office. State what extra hardware and software the company would have to supply to each copy editor to allow this communication. Give reasons for your answers.
- (i) State what is meant by an integrated (common) software package.
(ii) Give two reasons why an integrated software package would be used in the
- State what is meant by the
(i) hardware of a computer system,
(ii) software of a computer system.