A computer is a programmable machine. The two principal characteristics of a computer are: It responds to a specific set of instructions in a well-defined manner, and it can execute a prerecorded list of instructions (a program).
In this definition...
Modern computers defined
All general-purpose computers require the following hardware components:
- Memory: Memory enables a computer to store, at least temporarily, data and programs.
- Mass storage device: This allows a computer to permanently retain large amounts of data. Common mass storage devices include solid state drives (SSDs) or disk drives and tape drives.
- Input device: Usually a keyboard and mouse, the input device is the conduit through which data and instructions enter a computer.
- Output device: An output device is a display screen, printer, or other device that lets you see what the computer has accomplished.
- Central processing unit (CPU): The heart of the computer, this is the component that actually executes instructions.
- A motherboard: This component allows all of the other components to communicate with one another.
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Computer classification: by size and power
Most people associate a personal computer (PC) with the phrase computer. A PC is a small and relatively inexpensive computer designed for an individual user. PCs are based on microprocessor technology that enables manufacturers to put an entire CPU on one chip.
Personal computers at home can be used for a number of different applications including games, word processing, accounting, and other tasks.
Computers are generally classified by size and power as follows, although there is considerable overlap. The differences between computer classifications generally get smaller as technology advances, creating smaller and more powerful and cost-friendly components.
Personal computer: A PC is a small, single-user computer based on a microprocessor. In addition to the microprocessor, a personal computer has a keyboard for entering data, a monitor for displaying information, and a storage device for saving data.
Workstation: A workstation is a powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and a higher-quality monitor.
Minicomputer: A minicomputer is a multi-user computer capable of supporting from 10 to hundreds of users simultaneously.
Mainframe: A mainframe is a powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously.
Supercomputer: A supercomputer is an extremely fast computer that can perform hundreds of millions of instructions per second.
A computer has four main components: a CPU, a graphics processing unit (GPU), random access memory (RAM), and either a solid state drive (SSD) or a hard disk drive (HDD). All of these components are connected to a motherboard. Typically, the GPU and CPU comprise the computer’s chipset. The memory (RAM) and storage (SSD/HDD) components are typically easier to modify or replace than the chipset.
The first mechanical computer was developed in the early 19th century by Charles Babbage, an English engineer, and Ada Lovelace, a mathematician. At the computer’s core was the Difference Engine, which was responsible for making calculations using multiple sets of numbers printing the outputs.
The first digital computer was the Atanasoff-Berry Computer (ABC). The ABC was developed in 1942 by Iowa State University professor John Vincent Atanasoff and graduate student Cliff Berry. This computer used vacuum tubes to make binary computations and processed Boolean logic. However, the ABC lacked a CPU and was, therefore, not programmable. Subsequent computer evolutions added programming capabilities, RAM, transistors, microprocessors, and portability as key characteristics.
Recommended Reading: Webopedia’s Computer Architecture Study Guide is an introduction to computer system basics.