The Acorn A4 was the laptop version of the Acorn Archimedes and was one of the first RISC laptops (and by the way, one of the most powerful - five times faster than a 50 MHz 486 for some operations).
The operating system (RISC OS 3.10) was located in the 2 MB ROM. The 9'' LCD screen could only display 14 shades of grey, but used a clever dithering system to make more shades apparent.
The A4 could be used for about 3 hours with its internal batteries.
Rob Kendrick sent us more info :
The case is actually an Olivetti laptop case, with an A5000 in it. Olivetti owned large chunks of Acorn at the time. The main difference between an A5000 (a desktop machine) and a A4 is that the A5000 had a 16MHz memory bus and a 33MHz ARM3.
It had an advanced battery management unit that allows fine-grained control of the clock rate of the CPU (it can drop as low as 2MHz when the computer is idle and go back up to 24MHz when its busy) and the turning off of most of the hardware independently (such as the serial ports, floppy drive, hard drive etc)