Computers, computer hardware, and accessories are the focus of topics in this category.

A computer system consists of the hardware and software components. Computer software was discussed in the categories above. In this category and its subcategories, we will be covering the hardware components of a computer system, which are made up of electronic and mechanical parts. The main hardware components of a computer system are the processor, main memory, secondary memory, input devices, and output devices. This might be a desktop computer, a laptop, or a mobile device, and the components that make them up.

Many of a computer's components are connected to the motherboard, which is its main circuit board. The power supply provides the power for most of the components, and various input devices (keyboard, mouse, microphone, bar code reader, graphics tablet) and output devices (monitor, printer, speaker) are attached through connectors at the rear of the case. They may also be connected wirelessly, but they are still considered part of the computer hardware system.

The terms input and output refer to whether the data is flowing into or out of the computer. A bus is a group of wires on the main board of the computer. It serves as a pathway for data flowing between components. Most devices are connected to the bus through a controller, which coordinates the activities of the device with the bus. The processor is an electronic device, about an inch square, and covered in plastic. Inside the square is an even small square of silicon that contains millions of tiny electrical parts. Modern processors might contain billions of transistors. The processor is responsible for the fundamental computing within the system, directly or indirectly controlling all of the other components. The processor is the central processing unit, generally abbreviated CPU. Any particular type of computer will have a particular type of processors, such as an Athlon, Celeron, or Pentium processor.

The processor performs all of the fundamental computations, while other components contribute by taking on such tasks as storing data or moving data in and out of the processor.

A processor chip has just enough memory to hold a few instructions of a program and the data they process. All of the programs, applications, and utilities are held in memory external to the processor.

There are two types of memory: main memory and secondary memory. The main memory is volatile because it loses its information when the system is powered down. Secondary memory is generally nonvolatile, as it retains its information when the system is powered down, although it requires power when information is stored into memory or retrieved from it. The main memory may also be known as main storage, while secondary memory is secondary storage or mass storage.

When a computer program is booted up, or data is accessed, they are copied from secondary memory into main memory so that the processor can interact with them. However, a copy remains in secondary memory. Main memory is also known as RAM, which stands for random access memory. When a computer is said to have 5 GB of RAM, that is a reference to the size of the main memory, which would be stated in megabytes or gigabytes, although the RAM in early home computers was measured in kilobits. Nothing permanent is stored in main memory.

Secondary memory is where programs and data are stored long-term. Common secondary storage devices are the hard disk or the optical disk, although cloud storage has become popular.

Input/output devices are known as I/O devices and are directly connected to an electronic module attached to the motherboard, known as a device controller. In many computers, device controller functions are integrated with the motherboard.

A computer system that is part of a larger machine, and which controls how that machine operates, is known as an embedded system. Usually, the processor constantly runs a single control program that is permanently retained in read-only memory (ROM), which is used to make a section of the main memory read-only. This section of memory retains its data even when the power is off. The computer in a cellular phone is an embedded system, but embedded systems are also found in cars, digital cameras, and home appliances.

Also included as hardware are such components as the computer case, which encloses and holds most of the computer's components.

Accessories might include such hardware as flash drives and other external digital media, as well as any other hardware that might be used with a computer system, including cables and external protective products, such as laptop cases, computer carrying cases, and so on.

Retail sites for computers and computer hardware should be listed in the Computers category within the Shopping & eCommerce category or the appropriate Local & Global category.

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