Computers can be generally classified by size and power.At one end of the scale are supercomputers, very large computers with thousands of linked microprocessors that perform extremely complex calculations. At the other end are tiny computers embedded in cars, TVs, stereo systems, calculators, and appliances. These computers are built to perform a limited number of tasks. Personal computer: A small, single-user computer based on a microprocessor. The various kinds of personal computers: desktops, laptops, handheld computers, and Tablet PCs. a) Desktop computers: A desktop computer is a personal computer (PC) in a form intended for regular use at a single location. Most modern desktop computers have separate screens and keyboards. b) Laptops: A laptop has most of the same components as a desktop computer, including a display, a keyboard, a pointing device such as a touchpad (also known as a trackpad) and/or a pointing stick, and speakers into a single unit. A laptop is powered by mains electricity via an AC adapter, and can be used away from an outlet using a rechargeable battery. Laptops are also sometimes called notebook computers, notebooks, ultrabooks. c) Handheld computers: A Handheld PC, or H/PC for short, is a computer built around a form factor which is smaller than any standard laptop computer. It is sometimes referred to as a Palmtop. d) Tablet PCs: A tablet computer, or simply tablet, is a one-piece mobile computer, primarily operated by touch screen , removing the need for the physical (i.e., mouse and keyboard) hardware components necessary for a desktop or laptop computer; and, an onscreen, hideable virtual keyboard is integrated into the display. Available in variety of sizes. Workstation: A powerful, single-user computer. A workstation is like a personal computer, but it has a more powerful microprocessor and, in general, a higher-quality monitor. Minicomputer: A multi-user computer capable of supporting up to hundreds of users simultaneously. Mainframe: A powerful multi-user computer capable of supporting many hundreds or thousands of users simultaneously. Supercomputer: An extremely fast computer that can perform hundreds of millions of instructions per second. .