Win-98 and CPU's with HyperThreading

[Guest wsxedcrfv]

I know that win-9x/me are not multi-processor-aware, but I'm wondering if there are any known issues regarding win-9x stability if it's run on a processor with HT enabled in the bios. There are "suggestions" floating around on the net that you should disable HT for win-9x, but I'm wondering if there is anything of real substance behind such advice.

For example, I found these comments:

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Windows 98 cannot utilize the features of hyperthreading, and having it enabled may interfere with the way Windows 98 expects to handle threads.

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The following desktop operating systems are not recommended for use with Hyper-Threading Technology. If you are using one of the following desktop operating systems, it is advised that you should disable Hyper-Threading Technology in the system BIOS Setup program:

* Microsoft Windows* 2000 (all versions)

* Microsoft Windows NT* 4.0

* Microsoft Windows* Me

* Microsoft Windows* 98

* Microsoft Windows* 98 SE

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How would that differ if win-9x is running on a multi-core cpu?

[cluberti]

Any Intel chip that exposes HyperThreading theoretically should only have the registers used as a virtual processor if the OS running on it supports SMP, and since Win9x won't see that second logical CPU, it shouldn't be addressing it.

[BogdanV]

I never changed the HT support in BIOS and so far I haven't had any problems with my Prescott CPU.

[pointertovoid]

For Nt4 and W2k: they see each hyperthreaded core as two sockets and can use them as such. "Not HT aware" only means that their licence counts them as 2 cores or sockets. No instability to expect. But depending on your number of cores and on your licence, disabling HT forces Nt4/2k to prefer physically distinct cores or sockets, which is more efficient than hyperthreading a single core and neglecting the others.

I wouldn't believe a website which is already false on this point.

[cluberti]

Well, considering the bulk of the wiki answers document I believe the OP is referencing contains a straight rip from Intel's site, I'd at least trust them that disabling it isn't a bad idea.

As to disabling HT on 2K or NT, that's because the thread scheduler doesn't understand that the HT "CPU" is a virtual CPU or core, and will schedule it like any other physical CPU core in the system (which is inefficient and not what HT was designed to accomplish, thus depending on the workload you can actually be more efficient running one physical core rather than a physical+HT CPU in some scenarios). XP/2003 systems at least know to schedule on physical cores before scheduling a thread on an HT "core", and Vista and Win7 take their understanding further and can actually utilize the HT virtual CPUs much more efficiently - but that's neither here nor there in this discussion. It is likely safe to leave HT enabled on a CPU under Windows 9x, but disabling it in the BIOS won't hurt anything anyway, and Intel does recommend it for what it's worth, and it's their CPU architecture and design so they do carry some weight in the recommendation.