An excellent, almost definitive summary of the subject. I would just like to add a little of my own experiences. I have the real thing too (1962 mainframe) but also have an emulator for it. I initially wrote it so I could write software for it in the comfort of my house in the cold winter months without having to (a) risk damaging Germanium transistors which have a minimum official temperature rating of 50F, 10C. (b) having to warm up a whole barn to be comfortable to work in (c) having to hand start an old 3 phase 3.5 litre diesel generator with cold thick oil in it (d) having to pay for lots of diesel fuel or after I had 3 phase installed, to pay for 13 kWh electricity per hour. I now plan to publish my emulator on the web, along with original software which non programmers can run on it. I am very unsure of how many people will be interested in such a thing. I need to get the physical machine running to retrieve said software from unique ten track mag tapes and from standard 80 column cards, though I could probably get the latter read elsewhere, I don't want to have to transport about 150,000 card somewhere to have them read, probably at great cost. I am also into classic cars and hold an annual car show at my home attended by about 4000 people. The opportunity to try opening the door and show visitors the mainframe was too hard to resist, so we did and were very surprised by the results. No negative comments, even by children who were amazed that computers were ever so much bigger than their familiar home machines. It was surprising how many adults people had experienced mainframes and who loved being reminded of just what it had been like, and having the opportunity for their children to experience what words alone cannot really describe. The smell of hot electronics by the ton, the heat, the noise, and of course the sights of the whole thing and the main console with its flashing lights, the scale of a machine big enough that you can stand INSIDE it and being told it weighs five tons. In the early years I had to simulate some of what the machine should have done, by using diagnostic facilities and one or three instructions entered directly into the control registers when the machine had failed. If the machine ever completely failed and had to be shut down I certainly would be very disappointed and I feel the visitors would be too, I'm sure a static museum exhibit just does not have the same impact. I once visited Manchester museum and they had a couple of old mainframe. No explanation, nobody to ask, I could have been very interested and spent hours there but without any information I passed on to the next room in about two minutes. I have to say the temptation to try the on switch was hard to resist, there wasn't even anything saying not to do so. The same thing in the classic car scene. There are people who spend years building replicas of E Type Jaguars (called XKE in the US), D Type Jaguars, AC Cobras, 1930s roadsters etc, often with better performance/handling than the originals. Very nice people, and I'd rather they did that than modify a working original. Like many others, I take an original car which should really be scrapped and spend much time and money to bring it back to how it left the factory, often to a better build quality. A few people then sell them at a huge loss because it is the restoration process itself that they enjoy. I keep mine (I have never ever sold a car - scrapped a few though) and enjoy driving it. I have seven cars - six are roadworthy, one under restoration, postponed due to the amount of work on my classic computer. For micro computers I agree, not quite sure this applies to mainframes. I guess it depends on how you define software. If a single instruction is software then I suppose so. At the lowest level debugging I can set an instruction into control register one, set the machine to single cycle and watch the lights on the console as I send single clock pulses through the hardware every time I press a button. Not solely no. Just a useful side effect. Yes. Couldn't agree more. Yes but how can you give this experience to several hundred visitors in a day. With a multi-programmed machine this might be possible but with an older machine, specially ones without terminals (my one does not even have an operators terminal) you cannot do much without affecting the experience of the bulk of less technical visitors. I suppose it would be possible to provide an emulated machine to the minority but would they be interested in that? So that's why I'm a programmer? I don't really expect my programs to be around in 20 years time let alone a hundred. One member here did express approval for a program I wrote in the 1980s but that is exceptional. The program drove a particular colour dot matrix printer, very few of which survive, and is of no use whatever without that hardware, which in time will become extinct. Applications I've worked on could fare better but why would anyone want to run a 2D drafting program or a 3D modelling program on an emulated Mac in a hundred years time? For me I think its pleasing people NOW which matters, and of course the money to spend on cars, old computers, food etc As I am not going to live for ever I want my old computer to go to a museum. I've already tried with one which eventually went to a privately run museum as I could not GIVE it to a publicly run one. I would like this to happen to my remaining one whilst I am young enough to tell them how to move it, reassemble it and help get it running, I don't want to be doing it in my eighties, but I MIGHT still be interested in running an emulator which does not develop faults and need a resident engineer to fix them. One aspect of emulators I have not yet explored is, well hold on a second and I'll explain. When looking through the 1301's documentation, circuit diagrams and instruction set, I am very tempted to add improvement which could have been done by the designer, but for some reason, either budgetary or lack of knowledge (some software techniques had not been invented yet). In an emulator I could add indexing or indirect addressing, or immediate mode data, or relative mode, or branch on NOT some condition without having to modify the actual hardware. I could then try programming the machine in that configuration and see how it affected the program size and ease of programming. It would be even more fun if the emulator was done at logic gate level and even more so if mated to an interactive 3D model of the hardware where you could open the cover, insert emulated scope probes and look at the signals. You could even emulate random logic failures for educational reasons, though to do so as a game would probably be a step too far for me, though programming the emulator to do it WOULD be fun. Yes. Yes. The emulation page of the CCS web site seems to have disappeared so I can't check. As Colossus, like early US machines was not a stored program computer, I'm not sure at what level you want the emulation to run. I think there was an emulator for Baby, the first stored program computer on the web site. Never had a sealed in box machine which was beyond economic repair? :-) Absolutely.