What the heck! What is going on here? ... Doesn't the XT MB only have 8-bit slots? And how is the 486 upgrade not being severely bottlenecked? Wow.
Freaky, 'eh?
Yes, the system is ultimately bottlenecked by the XT motherboard's 8-bit bus, but I dropped a Cyrix 33/66MHz 486 133-pin compatible CPU on a vintage Intel Inboard/386 extension board that has its own 5MB of RAM that is fully addressable as extended, not expanded memory. That memory isn't bottlenecked and takes over after the initial bootstrap of the first 256K RAM off the main board. The 486 Cyrix gets clock limited to 33MHz by virtue of the InBoard's oscillator, which I could replace to get the full 66MHz, but haven’t as I'm not 100% comfortable soldering the 35-year old InBoard that is quite rare and now worth a small fortune. The Cyrix is also limited by it's own internal 1MB cache, but it still rips on Windows 3.1. Even though the InBoard plugs into the 8-bit bus, the limitation is the data transfer, not the processing and RAM, so, I get maximum performance of the 8-bit bus by replacing the MFM mechanical HDD with two 2GB solid-state drives connected via a an 8-bit XT-IDE adapter that many vintage computer builders have been building from kits to adapt newer drives to work with the older machines. With those mods, I get a monster built on an original IBM PC/XT chassis and original motherboard using 95% components that are from that era (save for the XT-IDE and CF).
While all of that is pretty freaky, the wow part is getting Win 3.1 to run - at all. The Intel InBoard was designed to run up to Win 3.0. Intel+Microsoft make a very rare and obscure version of Windows 3.0 (took me a long time to find a copy) that was created specifically for the Intel InBoard/386 (remember, an original 8088 PC couldn't dream of running Windows 3.0), and it was conventional wisdom that even with an Inboard/386, it could never Win 3.1 - but, but but....I figured out how to transplant key drivers from an Win 3.1 installation into the special Intel Win3.0 version and got- Volia! - A full-fledged edition of Win3.1 running perfectly - the "impossible" proven, possible. And if that isn't weird enough for you, I was able to get Win95 to boot, but that's where performance dives to the point its not an acceptable experience, so I run Calmira II with Win3.1 if I want to use a Win9x style GUI. For getting on the web I can run a few older browsers, but most use the Arachne browser to get around limitations of using IE 5.0 on modern sites.
All of the software I listed here (
https://pcpartpicker.com/b/krYrxr) runs like a champ - quite snappy. My subsequent project was another "it can't be done, impossible, no way" challenge - to run every version of DOS and Windows (multi-bot) up to at least Win7 32-bit on the same machine, without having to swap out any hardware between switching the OS, and having everything run properly per OS with all features enabled. Many 'expert' builders have tried and failed - and published their failures and insurmountable technical limitations in major publications, but as far as I am aware I'm the only one that has ever successfully created a build that overcame the so-called 'impossible' for that one. You can read about that freak here:
https://pcpartpicker.com/b/yJjcCJ
....but I digress badly. This is a thread about film and analog cameras and processing
Regards,
Mike