What is "not that fast enough" for OS/2 1.0, 1.1, 1.3?

[cprieto]

I heard OS/2, early versions, have problems booting and installing with a " fast" CPU (anything beyond 386 or 486 won't work, without modifying the binary). I was wondering, what does "fast" mean here? I mean, there are 100MHz 486 CPU's, is that "too fast" for OS/2 1.1?

I would love to know a little more about what is the max CPU speed (and type) needed for OS/2 1.0, 1.1 to run without changing the binary.

OS2Museum mentions 386 as "not that fast" enough to install 1.0-1.3 (see http://www.os2museum.com/wp/installing-os2-1-x-in-a-virtualbox-vm/) but then in some other documents 486 is good as well (https://www.os2museum.com/wp/os2-history/os2-1-1/).

[Dave Yeo]

Welcome to the forum Cristian,
You could always post to https://www.os2museum.com/wp/os2-history/os2-1-1/ (at bottom) and ask, Michal is usually pretty good about responding, at least if he has an answer.
I'd guess that things like cache would also make a difference so no hard boundary. OS/2 2.x used to be quite particular about cache and even failing with mismatched SIMS, sometimes needing everything possible to be slowed down/turned off in the BIOS.

[cprieto]

Thanks for welcoming me @Dave Yeo!

Yeah, I wrote a message to Michal, I am really interested in trying to install it in a physical machine (old versions) for "research purposes" so I want to collect as much information before getting into something that would be probably too hard to do

[Dave Yeo]

Wonder whether it is the speed or something else. Speed could screw up some loops and has broken a lot of software or it could be something else about CPU's (subtle changes in how some obscure instruction works for example) or even the whole system, like not being able to handle PCI. Lots of drivers that are needed to be updated at some point.
Be interested in your results once you try so hopefully you'll keep us posted on your attempts and hopefully successes.

[Eugene Tucker]

I have run OS/2 since May 1992 just after 2.0 was released. My first install was on a 486 /33 processor based system. I was a novice in computers and had no trouble installing it and soon learned to like it better than Dos and Windows 3.0. My computer sensei suggested I get it just to see how well I would do with it. I have preferred it ever since. I used to do everything In OS/2. And I support Arca OS.

[cprieto]

Ok, I had done a few tests... Because finding the hardware quickly is kind of difficult and I am pretty sure super expensive I used 86Box (https://github.com/86Box/86Box) to test different configurations. I started with the following setup:

Video card: Tseng4000AX, 1MB memory
RAM: 16MB
Motherboard: AMI386DX Clone
HDD: 35MB (remember, OS/2 only supports 32MB partitions)

I booted with the slowest 386DX/16 and did a clean OS/2 install and then I rebooted to see if OS/2 1.0 booted, these are the results for i386 CPUs:

CPU	Boots?
i386DX/16	yes
i386DX/20	yes
i386DX/25	yes
i386DX/33	yes
i386DX/40	yes
RapidCAD/25	yes
RapidCAD/33	yes
RapidCAD/40	yes

As expected, it boots... Remember, the RapidCAD CPUs wereh basically 486s for 386 sockets...

Now it is time for 486 CPUs, this is the used configuration:

Motherboard: AMI 486 Clone
RAM: 16MB
Video card: Tseng4000AX, 1MB memory
HDD: 35MB

And we reused the same installation image from previous tests, remember, we are trying to check if OS/2 boots:

CPU	Boots?
i486SX/16	yes
i486SX/20	yes
i486SX/25	yes
i486SX/33	yes
i486SX2/50	yes
i486SX2/66	yes
i486DX/25	yes
i486DX/33	yes
i486DX/50	yes
i486DX2/40	yes
i486DX2/50	yes
i486DX2/66	yes
i486DX4/75	no
i486DX4/100	no
Pentium Overdrive/63	no
Pentium Overdrive/83	no

As we may see here, nothing close to Pentium runs, so the limit is i486DX2 CPUs. Now the question is, can we run in those systems if we disable cache or some other things in the BIOS? Well probably, but I played with a few settings in the BIOS clock and disable all caches in the BIOS and even with those changes the i486DX4/75 didn't boot.

The lesson here is? OS/2 1.0 is really picky with the CPU speed, nothing bigger than a i486DX2/66 will even boot without doing the required changes in the installation files (as suggested in the links that I posted in the first question).

I hope this will help anyone else that ever have the same question, now I need to get a i486DX2 to play with