Information Technology · Ch 1 — Introduction to Computer System
The Computer System and Its Organisation
The Computer System and Its Organisation
A computer system is the complete working combination of hardware (the physical machine you can touch) and software (the instructions that make the hardware do useful work), together with the data it processes and the user who operates it. Neither hardware nor software is useful on its own — a computer without software is like a body without instructions, and software without hardware has nothing to run on.
The four basic operations. Whatever a computer does, it can be reduced to four basic operations that together form the information processing cycle:
- Input — data and instructions are fed into the computer through input devices.
- Processing — the CPU works on the data according to the instructions.
- Storage — data, instructions, and results are held in memory.
- Output — the finished results (information) are given out through output devices.
The functional units. To carry out these operations, a computer is organised into a few main functional units, often shown together as the block diagram of a computer:
- The input unit, which takes in data and instructions.
- The central processing unit (CPU), made up of the arithmetic and logic unit (ALU), the control unit (CU), and a small set of registers. The CPU is the "brain" that processes data and controls the whole system.
- The memory unit, which stores data and instructions — divided into primary (main) memory and secondary (auxiliary) storage.
- The output unit, which sends results out to the user.
Data flows from the input unit into memory, is worked on by the CPU, and the results move back to memory and out through the output unit. Running through all of this, the control unit sends the signals that keep every part working in step.
The four functional units and how they connect can be summarised as follows:
| Functional unit | Role | Data / control connections |
|---|---|---|
| Input unit | Takes in data and instructions | Sends data to the memory unit |
| Memory unit | Stores data, instructions, and results | Exchanges data with the CPU; receives from input; passes results to output |
| CPU — Control Unit (CU) | Fetches and decodes instructions and directs the system | Sends control signals to every other unit |
| CPU — Arithmetic & Logic Unit (ALU) | Performs arithmetic and logical operations | Processes data held in memory and returns results to it |
| Output unit | Gives the finished results to the user | Receives results from the memory unit |
Data flow: Input -> Memory -> CPU (processed by the ALU) -> Memory -> Output, while the control unit sends control signals to every unit so all parts work in step. …