What Intel CPUs Does ReactOS support?

[MugenFighter]

I would like to test ReactOS on an old computer (or if I can't get one build a computer that has hardware like an old computer), so what are the Intel CPUs that work on ReactOS?

[Pi_User5]

According to https://reactos.org/node/960:

Stefan Ginsberg wants a official decision on which CPU architecture we keep supporting at minimum in ReactOS. i386 was removed a while ago already and i486 is a problem now. In theory ROS code does not even boot at all anymore in it's current state on anything older than i586, but there are still many code parts in there for artificially keeping up the i486 support where it's not even existent in others. Official decision was never made for it, so he wants to know if he can ditch the i486 hacks spread around all over the ReactOS code or should add even more to make the existing ones of any use at all. The decision was made that all CPUs older than i586 without a own FPU will not be supported anymore in ReactOS due to the following reasons. No i486 would have the power to make any use of ReactOS anyways and due to the fact that we don't provide a Software FPU implementation, we have to rely on the way more advanced hardware solution. The same will result in no priority at all for ISA/EISA/MCA, because it's way too long outdated and of no use anymore these days

So I say i586.

But I'm not sure what CPU counts.

[Black_Fox]

Well, anything above 486 So Intel Pentium/AMD K5 and newer.

[jonaspm]

Pentium 4?

[Pi_User5]

Pentium 4?

My test rig has a Pentium III that works fine.

[EmuandCo]

i586 is Pentium, Pentoim Pro and MMX AND newer

[Swyter]

I remember enabling SSE2 support in the mbedTLS back-end for schannel.dll, so it you use native HTTPS (*) in something that does not support it the program will probably crash with an unknown opcode error.

It gives a nice speedup for anybody else, though, and SSE2 is really old. I guess it can be recompiled for legacy computers if needed.

(*) Like the built-in iexplore, downloading a RAPPS update or by using dwnl, other things like Firefox come with their own HTTPS/TLS/SSL back-ends.

[justincase]

I remember enabling SSE2 support in the mbedTLS back-end for schannel.dll

So, in other words, SSE2 support has to be disabled in mbedTLS if ReactOS is going to support i586, as the meeting minutes indicate it should?
If so, this is something that should be changed.

Is it not possible for mbedTLS to support running on CPUs that don't support SSE2, but also use SSE2 if it is available?
In other words, could SSE2 support be enabled, but lack-of-SSE2 be detected and worked around?

I read recently about a programmer who lazy-loads anything that isn't available in Windows 95 so that his programs can run on Win95+ and he either disables features that won't work on the older OSes, or works around the lack of certain things if possible.

[Swyter]

I remember enabling SSE2 support in the mbedTLS back-end for schannel.dll

So, in other words, SSE2 support has to be disabled in mbedTLS if ReactOS is going to support i586, as the meeting minutes indicate it should?
If so, this is something that should be changed.

Is it not possible for mbedTLS to support running on CPUs that don't support SSE2, but also use SSE2 if it is available?
In other words, could SSE2 support be enabled, but lack-of-SSE2 be detected and worked around?

I read recently about a programmer who lazy-loads anything that isn't available in Windows 95 so that his programs can run on Win95+ and he either disables features that won't work on the older OSes, or works around the lack of certain things if possible.

It supports querying extension support by using cpuid, but for this option in particular there's just a toggle switch at compile time. It's just a matter of commenting out that line up there. Disabling it shouldn't impact performance that much.

[williamwindley676]

Good to know! I've got an old Pentium 4 HT tower lying around and I've been wondering is react would run on it.