Informatics Practices · Ch 1 — Computer System
Introduction to Computer System
Introduction to Computer System
Every computing device, from the phone in your pocket to a huge machine running a website, does the same three things: it takes in data, works on that data, and hands back a result. A computer is an electronic device that can be programmed to accept data (the input), process it, and generate a result (the output). The word "programmed" matters — a computer does not decide on its own what to do. It follows a sequence of instructions given to it, and by changing those instructions the very same machine can be made to do entirely different jobs.
From computer to computer system
A bare computer on its own is of limited use. When a computer is combined with additional hardware and software, the complete working arrangement is called a computer system. A computer system primarily comprises four kinds of components:
- Central Processing Unit (CPU) — the component that actually carries out the processing.
- Memory — where data and instructions are held while work is in progress.
- Input/Output (I/O) devices — the means through which we feed data into the machine and receive results back from it.
- Storage devices — where data and programs are kept for later use.
None of these parts works in isolation. All the components function together as a single unit, and it is this coordination that delivers the desired output. Remove any one of them and the system cannot complete the input–process–output cycle.
Many forms, one design
Computer systems come in a variety of forms and sizes, yet the underlying organisation stays the same. The range runs from:
- a high-end server, at the most powerful end,
- through the personal desktop and the portable laptop,
- down to the tablet computer and the smartphone.
What changes across this range is scale, speed and portability — not the basic idea. A smartphone accepts input, processes it and produces output using exactly the same component structure as a server.
Reading the block diagram
The standard way to picture a computer system is a block diagram (Figure 1.1), in which each component — the CPU, the memory, the input and output devices, and the storage — appears as a block, and directed lines connect the blocks. These directed lines are not decoration: they represent the flow of data and signals between the components, so the direction of each arrow tells you which way information travels. Following the arrows lets you trace the complete journey of data, from the moment it enters through an input device to the moment a result emerges through an output device.
Alan Turing captured the ambition behind these machines memorably: a computer would deserve to be called intelligent if it could deceive a human into believing that it was human. The humble input–process–output box described here is the starting point of that story.
This section opens a chapter that goes on to trace the evolution of the computer, examine computer memory in detail, and study software — each building on the picture of the computer system set out here.
The figure is a block diagram — the standard schematic in which every component of the computer system is drawn as a labelled box and the connections between them are drawn as directed lines representing the flow of data and signals.
Down the middle runs a vertical stack. At the top sits a box labelled Secondary Storage Devices, joined by a double-headed arrow to the box below it, Primary Memory. Beneath Primary Memory is a shaded region labelled Central Processing Unit (CPU), and Primary Memory and this CPU region are likewise joined by a double-headed arrow. Inside the shaded CPU region are two boxes of its own: the Control Unit (CU) placed above the Arithmetic Logic Unit (ALU), with a double-headed arrow between them.
On either side of the CPU sit the two ovals. An oval marked Input Device on the left has a single arrow pointing into the CPU region, while an arrow leaves the CPU region and points out to an oval marked Output Device on the right.
The arrow directions carry the meaning of the diagram. The double-headed arrows — between secondary storage and primary memory, between primary memory and the CPU, and between the CU and the ALU — show that data and signals move in both directions along those paths: information is written to and read back from memory and storage, and the CU and ALU exchange signals as they work. The single-headed arrows at the sides show one-way traffic: input flows only inward from the input device, and results flow only outward to the output device. Taken together, the layout teaches the complete route data takes through a computer system — in through an input device, processed within the CPU (the CU directing, the ALU computing) in constant exchange with primary memory, preserved when needed in secondary storage, and finally delivered through an output device.