Computer Basics, Generations and Hardware

The word computer comes from 'compute', which means to calculate. Today a computer is an electronic device that accepts raw facts (data), processes them according to a set of instructions (a program), stores them if needed, and gives meaningful results (information). Remember the order: Input, Process, Output, with storage supporting all three.

Data is raw, unorganised facts (numbers, words, images). Information is data that has been processed and made meaningful. For example, marks of 50 students are data; the class average and topper's name are information.

Now the story of how we got here. People first used counting tools, then mechanical machines, and finally electronic machines. Every examiner loves the names on this journey, so read the timeline slowly.

Computers did not improve in a straight line; they improved in jumps, and each jump was caused by a new electronic component that made the machine smaller, faster and cheaper. We call each jump a generation. If you remember the component of each generation, you can answer almost every question on this topic. Dates differ a little from book to book, so learn the order and the component, not the exact year.

Now classify computers in three ways. By working principle (how they handle data), by size and power, and by purpose. The first way is the favourite of examiners.

By purpose, a general-purpose computer can run many kinds of programs (your laptop). A special-purpose (dedicated) computer is built for one job only, such as the chip inside a washing machine, an ATM or a traffic light. Such hidden computers are also called embedded systems.

The CPU (Central Processing Unit) is the brain of the computer. It fetches instructions from memory, understands them, and carries them out. A CPU on a single chip is called a microprocessor. Inside it there are three main parts: the ALU, the Control Unit and the Registers. Memory (RAM) and the hard disk are NOT parts of the CPU, even though the CPU works with them all the time.

This four-step loop is the machine cycle (fetch, decode, execute, store). Think of a restaurant: the Control Unit is the manager who reads the order, the ALU is the chef who cooks, the registers are the plates kept ready on the counter, and the result is served back.

How do we judge a CPU? The most common measure is clock speed, the number of cycles it completes per second, measured in hertz (Hz): MHz (millions) and now GHz (billions). A higher clock speed generally means more instructions per second. Other factors are the number of cores (a dual-core or quad-core CPU has two or four processing units on one chip), the size of the cache, and the word size (how many bits it handles at a time: 32-bit or 64-bit). Raw speed of old machines was quoted in MIPS (million instructions per second).

Everything the CPU needs sits on the motherboard, the main circuit board of the computer. All other parts plug into it or connect through it. The CPU talks to memory and devices through three sets of wires called buses: the data bus (carries data), the address bus (carries memory addresses) and the control bus (carries control signals).

A computer is useless if it cannot talk to us. Input devices carry our data and commands INTO the computer; output devices bring the result OUT in a form we can see, hear or hold. The one-line test: if you act on it to give something to the computer, it is input; if the computer gives something to you through it, it is output. A few devices do both.

Devices that do both input and output are called I/O devices. The classic examples are the touchscreen (you touch it to send commands, and it shows you the display) and the modem. A hard disk or pen drive also reads and writes data, but it is classed as a storage device.

Ports are the sockets at the back or side of the computer through which devices connect. Each port has a typical use, and the examiner often asks 'which port is used for monitor or audio or network'.

A computer is built from billions of tiny electronic switches, and a switch can only be ON or OFF. So the computer's natural language has only two digits: 1 (ON) and 0 (OFF). This is the binary number system. We humans count in ten digits because we have ten fingers; the machine counts in two because it has two switch states. Everything you see on a screen, a letter, a photo or a song, is finally stored as a long string of 0s and 1s.

The base (radix) of a system is the number of different digits it uses, and each position is a power of the base. In decimal, 345 means 3x100 + 4x10 + 5x1. In binary, 1011 means 1x8 + 0x4 + 1x2 + 1x1 = 11. Once you see this place-value idea, no conversion needs rote learning.

Codes: how do letters become 0s and 1s? Every character is given a number, and that number is stored in binary. ASCII (American Standard Code for Information Interchange) uses 7 bits, so it can represent 2⁷ = 128 characters; Extended ASCII uses 8 bits for 256. Unicode is the modern universal code that covers almost every script in the world, including Hindi (Devanagari), and its first 128 codes are the same as ASCII.

Computer questions love abbreviations. Learn the table below once; it covers most full forms asked in SSC, Railway and Police exams from this chapter. (Memory, software and Windows abbreviations appear in the next chapter.)