The Acorn A4 wasn't a complete design from scratch. Since Acorn was at the time part of the Olivetti group, it used existing stock from a PC laptop. One of the incarnations of this laptop was the Triumph Alder Walkstation, a 386SX25 PC with 4MB RAM. I have one of these, currently non-working.
As far as the machine goes, the case, screen, battery, floppy drive and DC/DC converter boards are shared between the A4 and the Walkstation. The Walkstation has an additional VGA board (with a Cirrus Logic VGA controller) which drives the LCD, an internal expansion bay (as the A4 but with a different connector, unfilled on mine), a 'docking station' connector, a tiny fan, a PCMCIA (?) socket and a rather nice touchpad behind the keyboard to the right. The touchpad has a 68HC805 microcontroller to drive it, and links to the motherboard with a couple of spare lines on the IDE cable. I'd be very interested to find out the protocol for this touchpad...
The April 1992 issue of Practical Electronics had an item on the Walkstation - also notice the rather early PhotoCD player:
Page by Theo Markettos (email at theo [at@] markettos.org.uk), last modified 2003-09-18
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