History: When I started my career, computers did not exist for the ordinery punter. They had been invented, of course, eg. Bletchley Park etc. but were not in common currency. Through college, tables and the slide rule were standard and simple calculating machines were being introduced. Where I worked the early number crunching was done on an Elliot 803 offsite, mainly by the mathematicians. Eventually an ICL mainframe was installed and the enthusiastic could batch process in Fortan and Algol. However, this was over the top for routine lab processing so someone very astutely got an early programmable calculator somewhere in the mid 1960s. This machine, the Olivetti Programma 101, was stupendously slow in that it flashed a light for each memory cycle and you could see the flashes! Nonetheless it could be programmed with a magnetic card and for complex calculations made the whole process quicker and more accurate. The language was like assembler but it had an arithmetic processor for all the standard mathematical functions. So I had to learn about arrays and indirection etc. This was followed by a faster Wang equivalent programmed with magnetic tape cassettes and later a Wang machine with a ROM Basic built in. It was a horrible Basic with most of the more structured statements missing so programs tended to end up like knitting but I enjoyed the process of programing using an interpreter where you can test your ideas out more or less on line.
Why I originally chose Acorn?: By the mid 1970's the modern micros were available and I toyed with the idea of my own computer. Despite considering the early Apples and the Commodore PET and the Sinclair etc. I felt that they had neither a good-enough specification, especially in respect of graphics, nor reputation for reliability. Then the BBC specification came out and at last I felt that this could be a machine that could do what I wanted. It had the best colour graphic spec. of the time a very nice ROM BASIC, a sound system, parallel, serial, analogue, and other ports, a cassette interface but upgradeable to floppy disc. I bought a Beeb around 1978 and had many years of enjoyment and service from it. In fact I still have it and it still works and plays a mean game of Repton! I suspect that most of the early Apples etc. are now in the bin! Sadly, being 8 bit and only with 32k of RAM it couldn't run a GUI and was usurped by the 16 bit machines in the 1980's despite being a better and more useful computer than any of IBM's early attempts.
Why I stayed with Acorn?: However the company that made it (Acorn) liked the style of the chip it used, the 6502, and decided that they would develop their own 32bit chip with all the good features of the 6502 and all the wish list features that the programming fanatics wanted such as lots of registers, a reduced instruction set (RISC), conditional operation of most instructions, most instructions processed in one clock cycle etc. This was introduced in the late 1980s in the form of the ARM chip in the Archimedes computer. The temporary, operating system was only a stopgap and RISCOS was issued around 1989. RISCOS is a nice consistent WIMP environment which is ROM based but easily extendable using modules. It has the advantage that the core OS can't be overwritten and can't be infected by a virus so it tends to be fairly stable. It also provides a fair range of services within the system so it unnecessary for every software developer to reinvent the wheel. Thus amost printing and character rendering, graphics, sound, comms, etc is handled by the system. This keeps the size of software to reasonable levels. For example a full wordprocessor / desktop publisher only takes about 1 megabyte and similarly for a fairly competent spreadsheet. Most software can interface with other software via interchangeable filetypes, and use of OLE in some cases.
Recent history: The development of the ARM processor was devolved to 'Arm Holdings' who license out the designs to other chipmakers. Because it has become a very widely used design it is now used in all sorts of gadgetry such as mobile phones, PDAs, car engine controllers, printer controllers etc. etc. The ARM system has more or less kept up with the INTEL style chips but is currently not available with the higher clock speeds. The latest processor suitable for use in a traditional RISCOS computer is the STRONGARM which is available up to 287mHz and it includes a lot of pipelining and cached data and programs. Intel now make chips under licence and are producing the Xscale chip using the ARM design. This is used as the basis of the Iionix which runs on a 600mHz Xscale chip using full 32 bit sofware. The market for ARM based computers is fairly small compared to WINTEL equivalent and consequently has a much smaller choice of software available but most of the common business applications are available and with some choice. The ARM chip is used because it has a low energy consumption and tends to be very efficient in terms of code, and hence program size. The most recent development is of a machine using the ARM9 chip.
Emulators: In the last five years emulators have been developed which can run on Windows-based machines. So now it is possible to have a machine running Windows XP which will run RISC OS and all the associated software as an alternative to native machines running on ARM hardware. I won't go any further now as there is probably hundreds of better sites out there which have more interesting stuff on the Computers. I'll just list a few sites to start off on if you wish to follow up this article.