A barebones PC is a computer that has minimal components. A typical barebones system includes a case, motherboard, CPU, hard drive, RAM, and power supply. Most barebones systems are sold as kits, in which the components must be assembled by the user.
Since barebones PCs usually do not come preassembled, they are not designed for the average computer user. Instead, barebones kits are aimed at computer enthusiasts and users who prefer to build their own PCs. By purchasing only specific components, a user can fully customize his computer system and avoid paying for unwanted extras. For example, if you buy a barebones kit, you can choose your own keyboard and mouse, since they are not included. Also, no software is bundled with barebones systems, so you avoid paying for software you don't need. Additionally, most barebones systems do not come with an operating system, so you can choose to install any operating system that is compatible with the hardware.
Nearly all barebones PCs are desktop computers since they are the most customizable. However, some companies also offer barebone laptop systems, or "barebooks," which can be homebuilt. While Macintosh computers now use most of the same components as PCs, the Mac OS X operating system requires proprietary hardware to run. Therefore, barebones systems are generally built to run either Windows or Linux.