What counts as hardware
Hardware is the physical part of a computer: the parts that can be touched, as opposed to the programs that run on them. The word comes from the older trade of selling metal tools and fittings, and it was applied to computers to separate the machine from its software. The terms below describe the most common parts, in roughly the order data flows through them.
The processor
The processor carries out instructions. It fetches an instruction, works out what it asks for, performs it and moves on to the next one. In most descriptions it is called the central processing unit, or CPU. In the earliest electronic machines the processor was built from many separate parts, such as vacuum tubes, and filled cabinets. Over time its circuits shrank, and the microprocessor, which put a whole processor on one chip, appeared in the early 1970s.
Modern machines often contain more than one processor. A core is an independent processing unit, and a chip with several cores can work on more than one task at once. A GPU, or graphics processing unit, is a processor specialized for image work and, in many systems, other tasks that can be split into many small parts.
Memory and storage
People often use “memory” and “storage” loosely, but they usually mean different things.
- Memory holds the programs and data in active use. It is fast, and in common designs it loses its contents when the power goes off. This is the RAM in most descriptions of a computer.
- Storage keeps programs and data for the long term. Examples over the decades include punched cards, magnetic tape, magnetic disks, optical discs and flash chips.
- Cache is a small, fast store placed close to a processor to keep frequently used data within quick reach. The word comes from a French term for a hiding place.
- Register is a tiny storage location inside the processor itself, used for the values it is working on at that moment.
A useful comparison is a desk and a filing cabinet. Memory is the desk surface where current work is spread out, and storage is the cabinet where everything else is kept. The comparison is rough, but it captures the difference in role.
Connecting the parts
- Bus. A set of wires or traces that carries data, addresses or control signals between components. The name suggests a vehicle that many passengers share, since many devices may use the same pathway. Computers usually contain several buses of different kinds.
- Motherboard. The main circuit board that holds the processor and memory and provides connections to other parts. Older documents sometimes call it a system board or mainboard.
- Chipset. A group of chips that coordinate traffic between the processor, memory and other devices.
- Port. A socket where a cable or device connects to the machine. The word was borrowed from shipping, where a port is a place of entry and exit.
- Controller. A circuit or small processor that manages a particular kind of device, such as a disk or a display, so the main processor does not have to handle every detail.
Input, output and peripherals
An input device sends data into the computer. Keyboards, microphones and, later, the computer mouse are common examples. An output device sends data out, such as a printer, a speaker or a display.
A peripheral is any device attached to the main computer. The word implies something at the edge, and the usual examples include keyboards, printers, scanners and external drives. In early large machines, peripherals were often big, expensive units of their own, such as tape drives or card readers. Today the distinction is blurrier: some devices that were once peripherals are built into the machine, and some parts of the machine can be removed and treated as peripherals.
An interface is the point where two components, or a person and a machine, meet. The word is used for both physical connections and software connections, so the context tells you which is meant.
Chips and circuits
- Transistor. A tiny electronic switch or amplifier. Transistors began replacing vacuum tubes in computers in the 1950s.
- Integrated circuit. A set of components made together on one piece of semiconductor material. Integrated circuits were developed in the late 1950s and became standard in computers in the following decades.
- Chip. Everyday name for an integrated circuit.
- Semiconductor. A material, silicon being the best-known, whose electrical behavior can be controlled, which makes it suitable for building switches.
Form factors and other labels
A form factor describes the physical size and shape of a device or component, such as desktop, tower or laptop. A server in hardware terms is a machine built mainly to provide services to others over a network, often without its own screen or keyboard. A terminal is a keyboard and display used to reach a distant computer; in time-sharing days, terminals had little computing power of their own.
A caution about names
Hardware words are used flexibly. A “drive” may mean a tape drive, a disk drive or a flash drive. A “board” may be a motherboard or a smaller add-on card. When reading historical material, look at the date and the machine being described, since the same word might point to quite different physical objects.