Homebuilt computer
A custom-built or homebuilt computer is a computer assembled from available components, usually commercial off-the-shelf (COTS) components, rather than purchased as a complete system from a computer system supplier, also known as pre-built systems.

Custom-built or homebuilt computer is usually considered cheaper to assemble as compared to buying a pre-built computer, since it excludes the labour associated with building a computer, and instead the labor is done by the end-user in assembling their own homebuilt computer.

Homebuilt computers are almost always used at home, like home computers, but home computers were traditionally purchased already assembled by the manufacturer. However, there were kits that were both home computers and homebuilt computers, like the Newbear 77-68, which the owner was expected to assemble and use in his or her home.

History 
Computers have been built at home for a long time, starting with the Victorian era pioneer Charles Babbage in the 1820s. A century later, Konrad Zuse built his own machine when electromechanical relay technology was widely available. In 1965, electronics engineer James Sutherland started building a computer out of surplus parts from his job at Westinghouse. The hobby really took off with the early development of microprocessors, and since then many enthusiasts have constructed their own computers.

Early examples include the Altair 8800 from the United States and the later British Newbear 77-68 and Nascom designs from the late 70's and early 80's. Some were made from kits of components, or simply distributed as board designs like the Ferguson Big Board. The Altair 8800 pioneered the S-100 bus which somewhat simplified the process.  Ultimately, the development of home computers, the IBM PC (and its derivatives and clones), and the industry of specialized component suppliers that grew up around this market in the mid 80's have made building computers much easier.  Computer building is no longer limited to specialists. Computers based on Apple Macintosh and Amiga computer platforms often can not be built in general by users legally because of patents and licenses for their hardware, firmware, and software.

Development as a hobby 

At one time building desktop PCs was a popular hobby. Not only could someone build a desktop that outperformed pre-built models selling in retail stores, but someone building their own computer may add whatever components they want, from multiple hard drives, case mods, high-performance graphics cards, liquid cooling, multi-head high-resolution monitor configurations, or using alternative operating systems without paying the "Microsoft tax". As pre-built computers improved in quality and performance, and manufacturers offered more options, it became less cost-effective for most users to build their own computers, and the hobby declined. The growing popularity of laptops and tablets led to a mobile first design methodology that is difficult for home builders to duplicate economically. Recently PC parts have become cheaper, and people are starting to build computers again. With the rise of virtual reality headsets (VR) such as the HTC Vive, the demand for high performance has risen. Competitive games with their own dedicated tournaments have brought about more builders due to more effective customization in performance.

Standardization 
Practically all PCs and some laptops are built from readily interchangeable standard parts. Even in the more specialized laptop market, a considerable degree of standardization exists in the basic design, although it may not be easily accessible to end-users. Although motherboards are specialized to work only with either Intel or AMD processors, all other parts like Graphic Processors, RAM, Chassis/Computer cases have been standardized to fit any setup. The availability of standard PC components has led to the development of small scale custom PC assembly. So-called white box PC manufacturers and commercial "build to order" services range in size from small local supply operations to large international operations.

Kits and barebones systems 
Computer kits include all of the hardware (and sometimes the operating system software, as well) needed to build a complete computer. Because the components are pre-selected by the vendor, the planning and design stages of the computer-building project are eliminated, and the builder's experience will consist solely of assembling the computer and installing the operating system. The kit supplier should also have tested the components to assure that they are compatible.

A barebones computer is a variation on the kit concept. A barebones system typically consists of a computer case with a power supply, motherboard, processor, and processor cooler. A wide variety of other combinations are also possible: some barebones systems come with just the case and the motherboard, while other systems are virtually complete. In either case, the purchaser will need to obtain and install whatever parts are not included in the barebones kit (typically the hard drive, Random Access Memory, peripheral devices, and operating system).

Like mass-produced computers, barebones systems and computer kits are often targeted to particular types of users, and even different age groups. Because many home computer builders are gamers, for example, and because gamers are often young people, barebones computers marketed as "gaming systems" often include features such as neon lights and brightly coloured cases, as well as features more directly related to performance such as a fast processor, a generous amount of RAM, and a powerful video card. Other kits and barebones systems may be specifically marketed to users of a free software operating system such as Linux or one of the BSD variants, with components guaranteed for compatibility and performance with that operating system.

Scavenged and "cannibalized" systems 
Many amateur-built computers are built primarily from used or "spare" parts. It's sometimes necessary to build a computer that will run an obsolete operating system or proprietary software for which updates are no longer available, and which will not run properly on a current platform. Economic reasons may also require an individual to build a new computer from used parts, especially among youth or in developing countries where the cost of new equipment places it out of reach of average people.

Advantages and disadvantages 
Building one's own computer affords tangible benefits compared to purchasing a mass-produced model, such as:
To make a computer customized to fit the user's needs in regard to quality, price, and availability.
To recycle an older computer, or to upgrade internal components such as the motherboard, CPU, video card, etc.
To build a high end computer using only top-quality parts for gaming, multimedia, or other demanding tasks.
To avoid trial software and other commission-driven additions that are made to mass-market computers prior to their being shipped.
To ensure the use of industry-standard parts for operating system compatibility or to upgrade the original build at a later date with little hassle.
To ensure that one has all the individual driver and OS discs - many manufactured computers only come with one or two discs, one containing the OS, and another containing the drivers required, plus all the shovelware that was initially installed. 
Enjoyment, personal satisfaction, and educational experience.
Tend to use higher quality parts as OEM's tend to user cheaper and lower quality parts.
In most cases, building a computer themselves is much cheaper when they compare the specifications.

There are drawbacks to building one's own PC:
A poorly designed system may have flaws that would be exposed during a manufacturer's testing. A case chosen on the basis of looks may have poor ventilation if the CPU is overclocked. 
Someone assembling a PC must educate themselves on how all the components work and how they interact, things like air flow, compatibility of each component with other components, space constraints inside the computer case, PCIe lanes and slots are some of the major points to educate themselves on before building a computer. Studying a guide on building and buying computer components is advised.
The lack of technical support and warranty protection other than what may be provided by the individual component and software vendors. However, a person assembling a PC likely has the expertise to maintain the system, and would require little assistance from manufacturers.
Finding certain components and knowing whether components are compatible or not without prior knowledge on PC parts.

Custom-built computers and alternative operating systems 

Because almost all mass-manufactured PCs ship with some version of Microsoft Windows pre-installed, individuals who wish to use operating systems other than Windows (for example, Linux or BSD) often choose to build their own computers. Their reason for doing so is not always related to saving money on an operating system.

Because Microsoft Windows is the de facto standard operating system for PCs, hardware device drivers of different qualities can readily be found that will enable virtually any component designed for the PC architecture to function on a Windows platform. However, the same isn't true for alternative operating systems like Linux and BSD, so these system users have to be careful to avoid hardware that is incompatible with their choice of operating system. Even among hardware devices that technically will "work" with these alternative operating systems, some will work better than others. Therefore, many users of non-Microsoft operating systems choose to build their own computers from components known to work particularly well with their preferred platforms.

A less common but still relevant option for people who choose to go another route when building their own PC and choosing their operating system may choose to configure what is called a Hackintosh system. This means that the user of the computer builds the computer specifically with the Mac OS in mind. This can often be a very tedious process as Apple has strict standards of what hardware they choose works with their software or not. Following previously built systems that worked is very important for success in this area. This is not generally a recommended route, but this hasn't stopped curious enthusiasts from achieving success.

Custom-built computers and high-performance systems 
Most mainstream manufactured computers use common or inexpensive parts such as onboard graphics and audio. While integrated accessories offer dramatic economic savings (and satisfy many users), these options generally do not perform as well as dedicated hardware under high demand situations such as current games, CAD and media production.

Homebuilt computers are most common among gamers, engineers, or other people who demand more performance from a specific component than the average user. An example would be a gamer using a slightly behind-the-curve CPU and disk drive, spending the difference on a more capable dedicated graphics card.

Additionally, those with more specific computer needs usually appreciate being able to upgrade certain components to fit their needs and the evolving needs of the software being used; in a typical manufactured PC the support components (such as power supply unit, motherboard, or even the chassis) are unfit for accepting high-performance add-in components. Constructing a system with future expansion in mind allows for such upgrades, which in turn are much cheaper than buying a brand new computer every time individual components become obsolete or insufficient to meet the needs of the user.

High-end PCs most often fall in the realm of heavy processor and/or memory usage applications such as a multimedia PC, home theater PC, music production, engineering, and many more. Generally a high-end system is capable of meeting the demands of gaming and can be used as such. A major difference between a high-end PC and a gaming PC is likely to only be the choice in video card since they will share a majority of other components. While a general-purpose high-end computer may be put to use in a render farm or as a file server, and be provisioned with components targeted at this use (such as a fast GPU for rendering or high-performance storage for serving files), most gaming takes place in real time so with a gaming PC all the components matter in creating a flawless and seamless experience. A less-intensive type of build satisfies or exceeds the needs of most computer users.

See also 
 White box (computer hardware)
 Hackintosh
 Barebone computer
 Enthusiast computing

References

External links

Personal computers
DIY culture