The Psion Series 3a is a palmtop computer sized at just 165mm x 85mm x 22mm (6.5" x 3.3" x 0.9"). It runs for months on two AA size batteries and fits comfortably in a jacket or jeans pocket. It never switches off, and has built-in Database, Time Managament, Word Processing and Spreadsheet facilities. The screen is 480x160 dots large and it can display black or grey pixels. In addition, the Series 3a incorporates a microphone and a loudspeaker for voice recordings and also for recording sounds to be used as alarms.
(This information was taken from a Psion press release)
The Series 3c (released in September 1996) is the same size as the 3a but has improved software. It has a faster serial port, infrared support, and is available with backlight display.
On June 16th 1997, Psion released the Series 5. It's the first machine of a new generation with a 32 bit ARM RISC processor running at 18,4 MHz. It features a backlight, touch sensitive display with a resolution of 640x240 pixels, infrared (IrDA) filetransfer and printing, patented keyboard and a slot for CompactFlash memory cards.
On June 15th 1999, Psion released the Psion Series 5mx. As the name says, it's an improved Series 5, with twice the speed (ARM710T at 36 MHz) and twice the RAM (16 MB). Also it has 10 MB compared to 6 MB of ROM. The backlight is brighter while using less power. There are a few new applications as well as many improvements on Word, Sheet and Agenda. Optionally, the Java Virtual Machine (JVM) can be installed giving access to a wide range of Java programs.