Path: utzoo!attcan!uunet!mcvax!ukc!mupsy!mucs!trevor From: trevor@ux.cs.man.ac.uk (Trevor Hopkins) Newsgroups: comp.arch Subject: OISC was Re: ZISC computers Keywords: OIC OISC Message-ID: <5183@ux.cs.man.ac.uk> Date: 29 Nov 88 14:18:06 GMT Organization: Computer Science, University of Manchester, UK Lines: 69 In a previous article Andrew Watson asked someone from Manchester to comment on the OIC developed here, well since I knew the guy who built the it I thought I might as well answer this one. Excuse any mistakes -- this is the first time I have posted to the net. Here are the details: J.R. Bown built a One Instruction Computer as his 3rd year undergraduate project at the University of Manchester. His report entitled `The One Instruction Computer' (third year project report No. 17, 1987) claims in its abstract to cover: The design and construction of a One Instruction Computer, OIC -- the extrapolation to its logical extreme of the philosophy of Reduced Instruction Set Computers, RISCs. The provision of a user environment for the testing and evaluation of software written for the One Instruction Computer Once Built. The instruction which this machine implemented was a Reverse Subtract Skip if Borrow, as described in previous postings. Just skipping through this report I came on a rather nice quote in his conclusions: Much to everyone's surprise, what at first sight appears to be a rather mad idea, namely a computer with only one instruction, appears in fact to have a great deal of potential as a viable machine. John actually built that machine and produced a fairly chunky report on it, which I have in front of me now. I don't know a lot about it so I`ll skim through the report and try and pick out the main points. His implementation used a 60ns basic cycle, with the number of cycles per instruction varying with the type of operands used. He built a cross assembler for the machine and was able to download programs into the OIC and upload the results. He also had an emulator program. A major section of the report gives details of the assembler and emulator. In the report he gives a number of comparisons of code written for the OIC and the corresponding versions for a PDP-11 -- the OIC code is 2 to 2.5 times larger. He concludes that optimisation of programs is extremely important and identifies 3 main types of optimisation: Functional: putting the emphasis on using subtracts wherever possible. Self Modifying code: - needed for indirect operations. Code re-ordering. He says his implementation was roughly equivalent to a 1 - 1.5 MIP PDP-11 type machine (whatever that means), but he describes some modifications which could be made to a future version of the machine which he says would make it nearly comparable to a 68020. He points out that the actual hardware for this machine could easily be fitted into one chip, together with a significant amount of memory. I hope this is of some use (or at least some interest) to some of you out there. Rhod _______________________________________________________________________ | Dept. of Computer Science JANET: rmd@uk.ac.man.cs.r5 | | The University USENET: mcvax!ukc!man.cs.r5!rmd | | Manchester M13 9PL Tel: +44-61-275 6149 | | U.K. | | ______ | | /~ ~\ So long and thanks for all the fish | | `-': :`-' | |____; ;_____________the mushroom project______________________________|