RISC World

Letters Page

It's all the's the letters page...

We have had a quiet couple of months on the letters front. This tends to happen over the later Summer and early Autumn. Now that the nights are drawing in I hope more readers will put finger to keyboard and drop us a line. Still, with my usual complaint about the number of letters over lets dive into the ones we can print...

Dear Editor,
I thought I'd write to you about how much I enjoy RISCWorld. Vol8 iss3 had an interesting article by Dave Holden. I agree with what he says about the strengths and limitations of RISC OS and I can see a market for VirtualRPC because it does make a lot of financial sense for anyone who habitually uses a RISC OS program; such as Impression style or FSIbatch. But most people today also want to make movies, surf the net and check their accounts on line. So VRPC is ideal. one thing that I think would be useful would be a version of RISC OS that would run any riscos program on any machine.
Changing the subject, do you buy crap cars on purpose just so you can have something to write about? Every issue I'm entertained by your latest motoring related exploits. I've never had to do any diy on my car, I'm amazed at how much welding and drilling and assembling you have to do to stay on the road. And you've included no photographs.
keep up the good work,
Laurence Simmonds

I am pleased that you are happy with RISCWorld. Our aim has always been to write the RISC OS magazine that we wanted to read. I still firmly believe that VirtualAcorn is the way to go for most users but I can accept that for some people it isn't suitable. I don't actually buy crap cars on purpose, I just buy cheap cars that happen to need work. Of course they are usually cheap because they need work. I have never subscribed to the "new car" philosophy for a number of reasons. Firstly new cars are a much bigger money pit than older vehicles. The depreciation on a new car is far greater then the amount I spend fixing older vehicles. Secondly older vehicles are far more environmentally friendly. This might sound a bit mad, but bear with me on this. Most of a vehicle's life time pollution is caused during the manufacturing process. If you buy a secondhand car and use it for two years, lets say 15,000 miles, then all the pollution you are creating is that caused by burning fuel, tyre wear on roads, oil etc. A new car has all these issues, plus has caused a lot of pollution in its manufacture. It's also far more environmentally friendly to repair rather then replace. So fixing an older vehicle so that it's then fit for purpose not only helps your wallet, it helps the planet.

Dear Aaron,
Please find attached a FrontEnd to an UnSqueeze Module. The motivation behind this was that I was using ArmAlyser looking at AIF !RunImages that had been run through !Squeeze. ArmAlyser attempts to UnSqueeze them, but I found it fell over, at least on both a Risc PC and the Virtual RPC.
You have no idea the trouble I had getting info about this off the Internet. Castle supplied the source code, but it is compressed in some weird format, and I have been unable to decompress it so far. The site provided compressed source code, which was not given a file type, so I managed to guess to type as 'Archive' on my RPC and decompress the file using David Pilling's !SparkFS. On finally getting the C code to compile and run (with quite a bit of difficulty), I found it was using its own form of compression and decompression, not the Acorn 5.00 one. Strong Help directed me to an obscure SWI called 'Service_UKCompress', that I eventually managed to discover was an unknown SWI on my RPC. I think it only existed under RISC OS 3.7. I even used OS_SWINumberToString to run through all the SWI numbers in the hopes of finding an obscure SWI that would perform the right type of decompression. The only form of compression/decompression it supports is Squash, it seems.
My actual intention was to design an application that would both Squeeze and UnSqueeze AIF files. Perhaps someone with more technical knowledge than me could do that better.
BTW I spent for ages trying to work out how on Earth the RISC OS operating system managed to distinguish between Squeezed and UnSqueezed AIFs. The file type is just the same. It's not in the 'load' or 'exec' addresses. The answer is that, right at the end of the Squeezed AIF, is a trailer with the characters 'rcc' and the compression version number in it followed by a fixed number of spaces. I was looking at the wrong end, expecting it to have some kind of special leader.

Thanks for this. I have included a copy of the UnSqueeze program in the letters section of the software directory on this issue. This is actually quite a serious problem for modern versions of RISC OS. You can end up with a situation where an executable designed for one version of RISC OS simply won't run on another. Not for any good reason, but simply because that version of RISC OS can't work out how to decompress the executable before running it. You may wonder why executables are compressed in the first place. Well as far as I can see there are only two reasons. Firstly space, a compressed one should be smaller. When we were all running from 800K floppy discs this might have been important, but that's ancient history. The other reason is to "hide" the code so that someone can't work out what it does. This is pointless as the code has to be decompressed to run, so an uncompressed copy is floating around in memory ready for someone to go and find.

I've e-mailed Martin privately about this application as I ran into a few problems with some things that it couldn't decompress, in this case the main !RunImage to the Pheonix browser. As a result he has made a few changes. Both of us would be interested in any results so let us know if you find the application useful.

Moving on, Laurence Simmonds also had this to say...

Dear Editor,
Why was there no mention of riscpcemulator last issue? Why not do - or get someone else to do - a review? Maybe include the software in the next issue? With an article on how to use it? Looking forward to the next issue.

Laurence Simmonds

This one had me going, so I e-mailed back and asked "what do you mean by 'riscpcemulator'? There are a number of different emulators that re-produce the RiscPC hardware, which one did you have in mind?". Laurence e-mailed me again and said:

Dear Editor,
I didn't know that. But now you've told me about them, why not do an article examining the different options. I know that there is at least one but I don't know anything about it or them. I suppose I could research the subject on the internet, but then why subscribe to RiscWorld?
Anyway, I enjoy the magazine, even the bits I don't understand.
Keep up the good work.
Laurence Simmonds

I am a bit reluctant to try and cover all the alternatives in detail but I can certainly explain which "Virtual" versions of the RiscPC do exist. Firstly there is VirtualAcorn, which is commercial and offers a number of pre-configured setups. I have a sneaking feeling that I might have mentioned this before somewhere (everywhere - DH). The website is at

Next come the freely available emulators. There is Red Squirrel. This is a cut down VirtualAcorn and is quite a lot slower, it comes with no ROMS or support but is very reliable but is only for Windows machines. Next up is RPCEmu, this is open source and has been ported to a number of platforms including Windows, Linux and Mac OS (PowerPC). Again this is supplied without ROMS or support. There were at least another one or two RiscPC emulators in existence at one time or another but a thorough Google search hasn't shown them up. So for now there is one commercial product and two freeware products that I can locate.

As for which is best? Well VirtualAcorn is the fastest and the most compatible and it is the only one which comes 'ready to go' with a complete hard disc image and operating system, but it costs money. Red Squirrel is similar to VirtualAcorn and it's easy to migrate from one to the other, but development isn't continuing at the moment. RPCEmu is being developed and can be run on lots of platforms but I personally have not had any success with getting the Windows version working on XP, which is a shame. It's worth trying either of the free ones to see how you get on, there are plenty of instructions available in the internet to help you get going.

As always if you would like to contact the RISCWorld letters page please e-mail us using the following e-mail address.

Aaron Timbrell