[2][3] Developed by Psion towards the end of the 1980s, informed by market research about the mobile computing needs of potential customers in the 1990s, the MC 400 was introduced in late 1989: an approximately A4-sized laptop or notebook computer featuring a full-size keyboard, 600 x 400 pixel monochrome liquid-crystal display and a multitasking, multi-window graphical user interface, providing a number of built-in applications in ROM.

Meanwhile, the MC 600 offered 768 KB of RAM (of which only 640 KB was accessible[5]) and a 1 MB RAM drive (acting as "drive C"[5]) in order to offer a viable DOS experience and thus raising the price to £1,495 plus VAT, with the display on this model providing CGA-compatible graphics support at a 640 x 200 resolution, albeit in monochrome.

The quality of the recorded speech was described euphemistically as "not brilliant", but "perfectly intelligible" and "quite adequate for note taking and interviewing".

The serial port also provides PC connectivity if used with the separately available PsiWin software using the lead designed for the Series 3 or 3A.

[8] Initial reactions were positive, with one describing the MC 400 as "a very good machine and as a top-end organiser it's a winner", but reservations were expressed at the lack of "more serious software" that would take advantage of the "super screen and keyboard".

[4] Some commentators welcomed the apparent simplicity of the MC 400, noting that the laptop market had embraced colour displays, CD-ROM drives, and in attempting to deliver a desktop-like experience had sacrificed battery life and robustness.

One praised "the MC-400’s 50-hour battery life, its near-perfect keyboard and its amazing durability" and claimed that in seven years of ownership, only Amstrad's NC100 and NC200 "has come close to producing anything better in terms of fitness for purpose".