Computer designed so the system unit, input devices, output devices, and any other devices fit entirely on or under a desk or table.
A small, portable computer - small enough that it can sit on your lap but fully functional. Often called notebook computers, use a trackpad.
A small computer which fits into your palm. Not powerful. May contain memory card slots. Battery powered. Stylus and touch screen.
special purpose computer that is built into another machine to control the machine and make it smart, eg aeroplane autopilot
A computer used in large organizations (eg hospitals, banks) that need to manage large amounts of centralised data. They can run multiple programs at the ame time for hundreds or thousands of users. Very very fast processor, very very high capacity memory and backing storage.