A desktop computer is a type of pc, or personal computer that is immobile, as opposed to a laptop computer or portable computer which can easily be moved. The first home computers were desktops, before advancements in microprocessor and other motherboard components made the development of the laptop computer possible.
The first commercially available desktop computer was the Altair 8800, starting in 1974. It contained the Intel 8800 chip and came with 1K of memory! Input was by way of toggle switches, and output by LEDs (light emitting diodes.) It was distributed by mail order, in kit form, and was quite popular. 
The demand for home computers did not go unnoticed and soon attracted competitors. The first big player in the pc market was Radio Shack, which introduced its Tandy computer line in the mid 1970s. The Tandy featured a keyboard and CRT monitor, which made interfacing with the computer much easier than the Altair, and was immediately successful. At the same time, two young entrepreneurs: Steve Wozniak and Steve Jobs, created their own version of the personal computer which they called the Apple. The Apple was quickly followed by the Apple II, which was introduced in 1977. The Apple II also used a keyboard that was somewhat similar to the Tandy, but more importantly,its monitor featured color graphics, as opposed to the monchrome of the Radio Shack computer.
Soon other players entered the market in the late 1970’s including: Atari with the Atari 400, Texas Instruments with the TI-99, and Commodore with the VIC-20. Commodore followed up on the VIC-20 with the Commodore 64 in 1982, so named because it had 64 kilobytes of memory. The Commodore 64 became one of the bestselling computers of all time and the competition soon led to a price war that eventually forced Texas Instruments out of the home computer business.
The 1980s saw several significant developments. In 1981, IBM finally entered the home computer market with the IBM PC. While not an immediate commercial success, it was the first computer to feature the MS-DOS operating system, licensed from Microsoft, which would soon become the standard. Standardization would enable computer users to use the same software on computers by different manufacturers, something which was not possible with earlier pc versions, which used proprietary operating systems. By the late 1980s nearly all personal computers manufacturers produced computers running the MS-DOS operating system, with the significant exception of Apple Computers.
During the same time period, processor and memory technology proceeded at a rapid pace. By the late 1980s computers with 32 bit processors and several hundred kilobytes of memory were common. Also during this time, Apple was pioneering the development of the GUI (graphical user interface), which allowed users to interact with their computers by means of icons and graphical displays, as opposed to text commands.
For more information on the history of personal computers from about.com, click here. For advice on buying a desktop computer from PC World, click here.
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