A Brief History of the Psion PDA
Created in about 1984. It had an alaphabetic keyboard (non QWERTY) and a one line LCD display. It had sliding plastic cover to protect the keyboard.
The Organiser II
An updated version of the Organiser. Typicaly it had 64k of memory and a 4 line display, although some versions had a 2 line display. Famed for being rugged they are still in use in some places for data collection. (For example within Psion I've seen them used within their repair and service depot to keep track of items)
The Series 3
Released in 1991 it was the first clam shell shaped organiser. It had 128k or 256k of memory and a full GUI which was driven by the keyboard. It had a full set of cut down office applications, such as a word processor and spreadsheet. It is also known as the 'Classic'.
The Series 3a
Launched in 1993, the 3a is a major update of the Series 3. It was made in several variants with 256k, 512k and then 1Mb and 2Mb of memory. It had a 480x160 screen and a multi-tasking operating system called SIBO.
The Series 3c
A further refinment of the 3c it came in 1Mb and 2Mb models. It also had a 57k serial port, a non-standard IR Port and, on some versions, a back light.
The Series 3mx
The last of the 3 Series range. The 3mx was released in 1998. It had a 115k serial port and came with 2Mb of memory as standard. It was discontinued in 1999.
The Series 5 'classic'
The Series 5 wasn't really much more than an overhaul of the Series 3. It was available from 1997. It had a touch screen, a new type of keyboard (real keys vs. the Series 3's rubber keys), a mutli-tasking 32bit OS and a standard IrDA port for connecting to computers and mobiles. It came with lots of software and had wireless internet access.
The Series 5mx
Released in June 1999. The 5mx had optimised software and an enhanced OS (EPOC v5). It came with 16mb of memory and had a faster processor. It also had a Java Virtual Machine (JVM) for browsing java-enabled web sites.
The Series 7
The Series 7 was launched in September 1999. It was aimed at the different market of sub-notebooks. It has a touch screen, CF and PC-Card slots and 16Mb of memory, expandable to 32Mb.
Released in October 1999, four months after the 5mx. The Revo is similar to the 5 Series. The main differences are that it is smaller, with a lower-res screen and smaller keys. It also featured built in rechargable batteries and no CF card slots. It has 8mb of RAM and a IrDA port for browsing the internet over a mobile phone.
The Revo Plus
The Revo Plus was launched in September 2000. It is the same as the Revo except that it came with 16Mb of memory, a port of the Opera browser and a Psion WAP browser.
Parts of this are based on information from http://3lib.ukonline.co.uk/historyofpsion.htm
The majority of it, however, is based on my experience of working with Psions and having worked (briefly) for Psion.