Back to the time where laptops weren't widely available and the personal computer just became feasible, portable computers were introduced.
A portable computer as its name suggests is designed to be moved from one place to another and includes a display and keyboard. By their nature, they are generally microcomputers and because of their size, are sometimes commonly known as 'Lunchbox' or 'Luggable' computers.
These are distinct from desktop replacement computers in that they are usually constructed from full-specification desktop components, and do not incorporate features associated with laptops or mobile devices. The principal advantage of a portable computer versus a laptop or other mobile computing device is the use of standard motherboards or backplanes providing plug-in slots for add-in cards. This allows mission specific cards such as test, A/D, or communication protocol (IEEE-488, 1553) to be installed. Portable computers also provide for more disk storage by using standard 3-1/2" drives and providing for multiple drives.
The IBM 5100
Back in 1973, the IBM Palo Alto Scientific Center developed a portable computer prototype called SCAMP (Special Computer APL Machine Portable) based on the IBM PALM processor with a Philips compact cassette drive, small CRT and full function keyboard.
The successful demonstrations of the 1973 SCAMP led to the first commercial IBM 5100 (pictured above) portable microcomputer launced in 1975. The product incorporated an IBM PALM processor, 5 inch CRT, full function keyboard and the ability to be programmed in both APL and BASIC for engineers, analysts, statisticians and other business problem-solvers.