Exploring the Psion MC400: A Vintage Mobile Computer

The Psion Mobile Computer, designed in the late 1980s and featuring several technologies that were leading-edge at the time. Launched in 1989 and sold for a few years into the early 1990s, a real marvel of 80s technology 😉 On the base of the machine it proudly states:
“© 1989 PSION PLC”.

The industrial design of the MC range was performed by Frazer (later work done by therefore), a team featuring Martin Riddiford (well-known for later award-winning design work for Psion including Series 3 and Series 5 designs) hence the family resemblance to the original Psion Series 3. It features an optional carrying handle that can be locked into position as a stand, raising the angle of the keyboard for more comfortable typing. Technically the MC was part of the same family as the original Series 3 and the HC – Psion’s industrial “handheld computer”. All of these machines featured an 80C86 processor with 2 custom Psion ASICs handling memory, I/O and other hardware access enabling very low power operation and instant suspend/resume.

The variant shown here is the MC400 featuring:

80C86 CPU running at 7.68MHz
256k RAM
Trackpad
640 x 400 mono LCD display (MC200 version was available with 640 x 200 screen)
4 x SSD slots for Psion proprietary Solid-State Disks
Psion’s proprietary fully multitasking windowed GUI OS (known as “EPOC” or “SIBO”) in 256k ROM
with built-in apps: Text Processor, Calendar/Diary, Personal “card file” database, Alarms, Calculator, File Manager, File Transfer (“The Link”), Terminal emulator and Psion’s “OPL” programming language.
full-size 60 key Cherry keyboard with an 8-key supplementary keypad
basic audio – integrated microphone and loudspeaker, piezo buzzer
2 x expansion ports at the rear – LH port fitted with RS-232 serial/parallel printer port module
Powered from removable battery packs (either: 10 x AA, 700mAH NiCd or 1.2AH NiCd) or AC/DC mains adapter. The NiCd packs are trickle-charged when in the machine or can be directly charged when removed with the machine’s AC/DC adapter. 10 x AA batteries power the machine for between 40-60 hours.

from https://frazerdesigners.com/computer-telecoms/

The last version sold by Psion was launched in 1992 and featured a new “professional” word processor application:

When the MC WORD (V2.60F) version GUI restarts the OS’s copyright statement shown is:
“PSION GRAPHIC USER INTERFACE
© 1989-91 Psion PLC”

Other commercially available software:
Psion’s official spreadsheet sold on SSD:

Spellcheck & Thesaurus SSD for the Series 3 also compatible with the MC WORD:

DOS-based connectivity software to transfer files to/from a DOS PC:

Other software for the MC can be found at: https://github.com/zedstarr/MC400_ROM/tree/main/software

A gallery of screenshots from the Psion MC400 of some of the standard built-in apps:

Hardware disassembly guide and teardown photos available here: https://zedstarr.com/psion-mc400-disassembly-guide/

Development work still ongoing (as of Aug 2024) to emulate the hardware in MAME: https://zedstarr.com/2022/06/15/psion-mc400-rom-dump-emulation/

UPDATE: 31/12/2024: MAME 0.273 and later now include emulations of the MC200, MC400 and MC Word 😉 https://zedstarr.com/2024/12/31/psion-mc400-emulated/

The MC was supplied with a detailed set of manuals: Operating Guide, Programming Guide (both ~300 pages each), Word Processor (~100 pages) and Spreadsheet (~150 pages) manuals.