Computer - A machine that can be programmed to manipulate symbols. Computers can perform complex and repetitive procedures quickly, precisely and reliably and can quickly store and retrieve large amounts of data.

Monitor - A cathode-ray tube and associated electronics connected to a computer's video output. A monitor may be either monochrome (black and white) or color (RGB). Color monitors may show either digital color (each of the red, green and blue signals may be either on or off, giving eight possible colors: black, white, red, green, blue, cyan, magenta and yellow) or analog color (red, green and blue signals are continuously variable allowing any combination to be displayed). Digital monitors are sometimes known as TTL because the voltages on the red, green and blue inputs are compatible with TTL logic chips.

Keyboard - A hardware device consisting of a number of mechanical buttons (keys) which the user presses to input characters to a computer. Keyboards were originally part of terminals which were separate peripheral devices that performed both input and output and communicated with the computer via a serial line. Today a keyboard is more likely to be connected directly to the processor, allowing the processor to scan it and detect which key or keys are currently pressed. Keyboards vary in the keys they have, most have keys to generate the ASCII character set as well as various function keys and special purpose keys, e.g. reset or volume control.

Mouse - The most common kind of pointing device. A mouse is moved over a flat horizontal surface and includes some means of converting its position in two dimensions into X-Y coordinates which the computer can read. It also has one or more buttons whose state can also be read. It is called a mouse because the wire connecting it to the computer or keyboard looks like a mouse's tail. The two commonest types of mouse are rolling ball and optical.

Peripheral - <hardware> (Or "peripheral device") Any part of a computer other than the CPU or working memory, i.e. disks, keyboards, monitors, mice, printers, scanners, tape drives, microphones, speakers, cameras, to list just the less exotic ones. High speed working memory devices, such as RAM, ROM, or, in the old days, core would not normally be referred to as peripherals.

Modem - (Modulator/demodulator) An electronic device for converting between serial data (typically RS-232) from a computer and an audio signal suitable for transmission over telephone lines. In one scheme the audio signal is composed of silence (no data) or one of two frequencies representing 0 and 1. Modems are distinguished primarily by the maximum baud rate they support. Baud rates can range from 75 baud up to 56000 and beyond. Data to the computer is sometimes at a lower rate than data from the computer on the assumption that the user cannot type more than a few characters per second.

 Floppy Drive - A peripheral device that reads and writes hard disks or floppy disks.

Floppy Disk - (Or "floppy", "diskette") A small, portable plastic disk coated in a magnetisable substance used for storing computer data, readable by a computer with a floppy disk drive. The physical size of disks has shrunk from the early 8 inch, to 5 1/4 inch ("minifloppy") to 3 1/2 inch ("microfloppy") while the data capacity has risen. These disks are known as "floppy" disks (or diskettes) because the disk is flexible and the read/write head is in physical contact with the surface of the disk in contrast to "hard disks" (or Winchesters) which are rigid and rely on a small fixed gap between the disk surface and the heads. Floppies may be either single-sided or double-sided. 3.5 inch floppies are less floppy than the larger disks because they come in a stiff plastic "envelope" or case, hence the alternative names "stiffy" or "crunchy" sometimes used to distinguish them from the floppier kind.

Hard Drive - A disk drive used to read and write hard disks.

Hard Disk - (In contrast to floppy disk). One or more rigid magnetic disks rotating about a central axle with associated read/write heads and electronics, used to store data. Most hard disks are permanently connected to the drive (fixed disks) though there are also removable disks.

CPU - (CPU, processor) The part of a computer which controls all the other parts. The CPU fetches instructions from memory and decodes them. This may cause it to transfer data to or from memory or to activate peripherals to perform input or output.

I/O - Input/Output. Communication between a computer and the user or the outside world.

Input device - A peripheral used to transfer data from the outside world into a computer system. Some input devices are operated directly by the user, e.g. keyboard, mouse, touch screen, joystick, digitizing tablet, microphone; others are sensors or transducers which convert external signals into data, e.g. using an analog to digital converter (this would also be true of a microphone).