A desktop computer is a personal computer that fits on or under a desk. They usually consist of a monitor, keyboard, mouse and either a horizontal or vertical(tower) form factor.
A portable computer with an LCD screen that weighs from two to 10 pounds. It uses batteries for mobile use and AC power for charging and desktop use. High-end laptops provide nearly all the speed and capabilities of desktop computers.
A workstation is a special computer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems.
In information technology, a server is a computer program that provides services to other computer programs (and their users) in the same or other computers. The computer that a server program runs in is also frequently referred to as a server (though it may be used for other purposes as well).
Software can be thought of as the variable part of a computer. Software is often divided into applicationsoftware (programs that do work users are directly interested in) and system software (which includes operating systems and any program that supports application software).