After the release of the A5000, Acorn decided to enter the portable computer market, and so, in mid-1992 the Acorn A4 was launched.
There seems to be some doubt as to whether this machine was an A5000 in a portable sized box, or the A5000 was an A4 in a desktop box, but either way the A4 was a very impressive technological achievement.
The A4 was based on an ARM3, although it was clocked at 24 MHz, rather than the higher speeds of the A540 or A5000. The memory was clocked at 12 MHz, and the display controller at 36 MHz. Two models were available, one with 2 Mb of memory and no hard drive, and one with 4 Mb of memory and a 60 Mb IDE hard drive. The system weighed roughly 3 kg, and the case really did have the same footprint as an A4 piece of paper.
Both A4 models featured a 640 by 480 pixel 15 grey scale passive matrix LCD panel, a 1.6 Mb floppy drive, an 83 key keyboard, a parallel port. a serial port, a headphone socket and sockets for an external mouse and keyboard. Although it was possible to emulate the mouse using key-combinations, generally the A4 was intended to be used with the external mouse. No podule slots were included, due to the restricted space available in the case. The A4 was supplied with a slightly later version of RISC OS 3 than the A5000, with the main differences being the addition of the power management software and some bug fixes.
A number of power management features were included with the A4. These included a redesign of the sound system, so that it only used approximately a tenth of the power needed by the A5000 sound system, and the ability to shut down the hard drive and LCD panel. The power management system could also detect when the system was idling and reduce the clock speed of the processor (from 24 MHz to 6 Mhz) and memory (from 12 MHz to 3 MHz), reducing the consumed power by roughly a quarter. Acorn claimed that with all the power management enabled, a battery life of 2.5 to 4 hours was possible.
The A4 was not without its problems. The various ports on the machine were protected with plastic flaps, which were vulnerable to damage, and the keyboard layout was also more along the lines of a PC keyboard, rather than the Acorn model. The A4 was also considerable more expensive than the (386) laptops available at the time - the A4 cost £1399 excluding VAT for the base model and £1699 excluding VAT for the higher specification model, compared to about £1000 for a PC laptop. These negative points were offset, however, by the fact that the A4 was a true descendant of the Archimedes range, and would run any software that could run on RISC OS 3 on an A5000 (and didn't require podule hardware).
The A4 remained in Acorn's range for a number of years, and turned out to be the company's only entry in to the world of portable computing.
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