Computer hardware (usually simply called hardware when a computing context is implicit) is the collection of physical elements that constitutes a computer system. Computer hardware is the physical parts or components of a computer, such as the monitor, mouse, keyboard, computer data storage, hard disk drive (HDD), system unit (graphic cards, sound cards, memory, motherboard and chips), and so on, all of which are physical obects that can be touched (that is, they aretangible).!"# $n contrast, software is instructions that can be stored and run by hardware.%oftware is any set of machine&readable instructions that directs a computer's processor to perform specific operations. ( combination of hardware and software forms a usable computing system.!)#*on +eumann architecture!edit#Main article: Von Neumann architecture*on +eumann architecture scheme.,he template for all modern computers is the *on +eumann architecture, detailed in a "-./ paper by Hungarian mathematician 0ohn von +eumann. ,his describes a design architecture for an electronic digital computer with subdivisions of a processing unit consisting of an arithmetic logic unit and processor registers, a control unit containing an instruction register and program counter, a memory to store both data and instructions, external mass storage, and input and outputmechanisms.!1# ,he meaning of the term has evolved to mean a stored&program computer in which an instruction fetch and a data operation cannot occur at the same time because they share a common bus. ,his is referred to as the *on +eumann bottleneck and often limits the performance of the system.!.#%ales!edit#2or the third consecutive year, 3.%. business&to&business channel sales (sales through distributors and commercial resellers) increased, ending )4"1 up nearly 5 percent at 65".7 billion. ,he impressive growth was the fastest sales increase since the end of the recession. %ales growth accelerated in the second half of the year peaking in fourth 8uarter with a 5.- percent increase over the fourth 8uarter of )4").!/#Different systems!edit#,here are a number of different types of computer system in use today.Personal computer!edit#Hardware of a modern personal computer". 9onitor ).9otherboard 1.C:3 .. ;(9 /.. Hard disk drive -.?eyboard "4.9ouse$nside a custom&built computer@ power supply at the bottom has its own cooling fan.,he personal computer, also known as the :C, is one of the most common types of computer due to its versatility and relatively low price. Aaptops are generally very similar, although may use lower&power or reduced siBe components.Case!edit#Main article: Computer case,he computer case is a plastic or metal enclosure that houses most of the components. ,hose found on desktop computers are usually small enough to fit under a desk, however in recent years more compact designs have become more common place, such as the all&in&one style designs from (pple, namely the i9ac. Aaptops are computers that usually come in a clamshell form factor, again however in more recent years deviations from this form factor have started to emerge such as laptops that have a detachable screen that become tablet computers in their own right.Power supply!edit#Main article: Power supply unit (computer)( power supply unit (:%3) converts alternating current ((C) electric power to low&voltage DC power for the internal components of the computer. Aaptops are capable of running from a built&in battery, normally for a period of hours.!5#Motherboard!edit#Main article: Motherboard,he motherboard is the main component of computer. $t is a large rectangular board with integrated circuitry that connects the other parts of the computer including the C:3, the ;(9, the disk drives(CD, D*D, hard disk, or any others) as well as any peripherals connected via the ports or the expansion slots.Components directly attached to or part of the motherboard include@ ,he CPU (Central :rocessing 3nit) performs most of the calculations which enable a computer to function, and is sometimes referred to as the CbrainC of the computer. $t is usually cooled by a heat sink and fan. 9ost newer C:3s include an on&die Draphics :rocessing 3nit (D:3). ,he Chipset, which includes the north bridge, mediates communication betweenthe C:3 and the other components of the system, including main memory. ,he Random-Access Memory (;(9) stores the code and data that are being actively accessed by the C:3. ,he Read-Only Memory (;=9) stores the E$=% that runs when the computer is powered on or otherwise begins execution, a process known as Eootstrapping, or CbootingC or Cbooting upC. ,he BIOS (Easic $nput =utput %ystem) includes boot firmware and power management firmware. +ewer motherboards use 3nified