Computer hardware are the physical parts or components of a computer, such as monitor , keyboard, computer data storage , graphic card , sound card and motherboard .  By contrast, software is instructions that can be stored and ran by hardware.
Hardware is directed by the software to execute any command or instruction . A combination of hardware and software forms a usable computing system.
Von Neumann architecture
The template for all modern computers is the Von Neumann architecture , detailed in a 1945 paper by Hungarian mathematician John von Neumann . This Describes a design architecture for an electronic digital computer with subdivisions of a processing unit consistant en an arithmetic logic unit and processor registers , a control unit Containing an instruction register and program counter , a memory to store Both data and instructions , external mass storage , and input and outputMechanisms.  The meaning of the term has been evolved to mean a stored-program in which an instruction fetch and a data operation can not occur at the same time because they share a common bus . This is referred to as the Von Neumann bottleneck and often limits the performance of the system. 
For the third consecutive year, US business-to-business channel sales (sales through distributors and commercial resellers) increased, ending 2013 up nearly 6 percent at $ 61.7 billion. The growth is growing faster than the end of the recession. Sales growth accelerated in the second half of the year with a 4.9 percent increase over the fourth quarter of 2012. 
There are a number of different types of computer system in use today.
The personal computer , also known as the PC, is one of the most common types of computer software and its versatility and relatively low price. Laptops are generally very similar, they may use lower-power or smaller size components, thus lower performance.
The computer case encloses most of the components of the system. It provides mechanical support and protection for internal elements such as the motherboard, disk drives, and power supplies, and controls the flow of cooling air over internal components. The case is also part of the system to control the electromagnetic interference radiated by the computer, and its internal part from electrostatic discharge. Large tower cases provide more space for multiple disk drives or other devices and usually stand on the floor, while desktop boxes provide less expansion room. All-in-one style designs from Apple , namely the iMac, and similar types, include a video display built into the same case. Portable and laptop computers require boxes that provide impact protection for the unit. A current development in a laptop is a detachable keyboard, which allows the system to be configured as a touch-screen tablet. Hobbyists may decorate the boxes with colored lights, paint, or other features, in an activity called case modding .
A power supply unit (PSU) converts alternating current (AC) electric power to low voltage DC power for the internal components of the computer. Laptops are capable of running from a built-in battery, normally for a period of hours. 
The motherboard is the main component of a computer. It is a board with integrated circuitry that connects the other parts of the computer to the CPU , the RAM , the disk drives ( CD , DVD , hard disk , or any others) as well as any peripherals connected through the ports or the expansion slots .
Components directly attached to or part of the motherboard include:
- The CPU (central processing unit), which performs most of the calculations which enable a computer to function, and is sometimes referred to as the brain of the computer. It is usually cooled by a heatsink and fan, or water-cooling system. Most newer CPUs include an on-die Graphics Processing Unit (GPU) . The clock speed of CPUs is fast, it is measured in GHz; typical values between 1 GHz and 5 GHz. Many modern computers have the option to overclock the CPU which enhances the performance of a greater thermal output.
- The chipset , which includes the north bridge , communication between the CPU and the other components of the system, including main memory.
- Random-access memory (RAM), which stores the code and data that is used by the CPU. For example, when a web browser is opened on the computer it takes up memory; this is stored in the RAM until the web browser is closed. RAM usually comes on DIMMs in 2GB, 4GB, and 8GB sizes, but can be much larger.
- Read-only memory (ROM), which stores the BIOS as it executes when executing bootstrapping , or ” booting ” or “booting up”. The BIOS (Basic Input Output System) includes boot firmware and power management firmware. Newer motherboards use Unified Extensible Firmware Interface (UEFI) instead of BIOS.
- Buses that connect the CPU to various internal components and expand cards for graphics and sound.
- The CMOS battery , which powers the memory for date and time in the BIOS chip. This battery is a watch battery.
- The video card (also known as the graphics card), which processes computer graphics. More powerful graphics cards are better suited to handle strenuous tasks, such as playing intensive video games.
An expansion card is a circuit board that can be inserted into an expansion slot of a computer motherboard or a backplane to add functionality to a computer system via the expansion bus. Expansions cards can be used to obtain or expand by the motherboard.
A storage device is any hardware and digital media that is used for storing, porting and extracting data files and objects. It can hold and store information only and permanently, and can be used internally or as a computer, server or any other similar computing device. Data storage is a core function and fundamental component of computers.
Data is stored by a computer using a variety of media. Hard disk drives are more or less expensive, but they are more efficient and more cost – effective, but they are more expensive than they are.  N / A are often found in personal computers built post-2007.  Some systems may use a disk array controller for greater performance or reliability.
To transfer data between computers, a USB flash drive or optical disc may be used. Their usefulness depends on being readable by other systems; the majority of machines have an optical disk drive, and virtually all have at least one USB port.
Input and output peripherals
Input and output devices are typically housed externally to the main computer chassis. The following are either standard or very common to many computer systems.
Input devices allow the user to enter information into the system, or control its operation. Most personal computers have a mouse and a keyboard , but laptop systems typically use a touchpad instead of a mouse. Other input devices include webcams , microphones , joysticks , and image scanners .
Output devices display information in a human readable form. Such devices could include printers , speakers , monitors or a braille embosser .
A mainframe computer is a much larger computer that typically fills a room and has a personal computer. They are designed to perform large numbers of calculations for governments and large enterprises.
In the 1960s and 1970s, more and more departments started to use Cheaper and dedicated systems for Specific Purposes like process control and laboratory automation .
A supercomputer is superficially similar to a mainframe, but is instead intended for extremely demanding computational tasks. As of June 2016 , the fastest supercomputer in the world is the Sunway TaihuLight , in Jiangsu , China. 
The term supercomputer does not refer to a specific technology. Rather it says the fastest computations available at any given time. In mid 2011, the fastest supercomputers boasted speeds over one petaflop, or 1 quadrillion (10 ^ 15 or 1,000 trillion) floating point operations per second. Super computers are fast and extremely costly so they are used by broad organizations to execute computationally demanding tasks involving large data sets. Super computers typically run military and scientific applications. Although they cost millions of dollars, they are also used for commercial applications where huge amounts of data must be analyzed. For example, large banks employ supercomputers to calculate the risks and returns from various investment strategies,
When using computer hardware, an upgrade means adding new hardware to a computer that improves its performance, adds capacity or new features. For example, a user could perform a hardware upgrade to replace the hard drive with a SSD to get a boost in performance or increase the amount of files that can be stored. Also, the user could increase the RAM more smoothly. The user could add a USB 3.0 expansion card in order to fully use USB 3.0 devices, or could upgrade the GPU for extra rendering power. Performing such hardware upgrades may be required for older computers to meet a system requirements.
Because computer parts contain hazardous materials, there is a growing movement to recycle old and outdated parts.  Computer hardware contains dangerous chemicals such as: lead, mercury, nickel, and cadmium. According to the EPA these e-wastes have a harmful effect on the environment unless they are disposed of properly. Making hardware requires energy, and recycling units will Reduce air pollution , water pollution, as well as greenhouse gas emission.  Disposing unauthorized computer equipment is in fact illegal. Legislation makes it mandatory to recycle computers through the governmentapproved facilities. Recycling a computer can be made easier by taking out some reputable parts. For example, the RAM , DVD drive, graphics card , hard drive or SSD , and other similar removable parts can be reused.
Toxic computer components
The central processing unit contains many toxic materials. It contains lead and chromium in the metal plates. Resistors, semi-conductors, infrared detectors, stabilizers, cables, and wires containing cadmium. The circuit boards in a computer containing mercury, and chromium.  When these types of materials, and chemicals are improperly disposed of hazardous for the environment.
According to the United States Environmental Protection Agency only around 15% of the e-waste actually is recycled. When e-waste byproducts leach into ground water are burned or get mishandled during recycling it causes harm. Such problems include impaired mental development, cancer, and damage to the lungs, liver, and kidneys.  That’s why even wires have to be recycled. Different companies have different techniques to recycle a wire. The most popular one is the grinder that separates the copper wires form the plastic / rubber casing. When the processes are done there are two different piles left; one containing the copper powder, and the other containing plastic / rubber pieces.  Computer monitors,mice , and keyboards all have a similar way of being recycled. For example, first of all, the parties are taken from their homes and their places of origin. 
Recycling a computer is made easier by a few of the national services, such as Dell and Apple . Both companies will take back the computer of their make or any other make. Otherwise a computer can be donated to Computer Aid International which is an organization that recycles and refurbishes old computers for hospitals, schools, universities, etc. 
- Computer architecture
- Electronic hardware
- Glossary of computer hardware terms
- History of Computing Hardware
- List of computer hardware manufacturers
- Open-source computing hardware
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