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Slowing P133 down on DOS.

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First post, by daeds

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Hello there! 😀
Another day, another question.
I'm going to install MSDOS 6.22 on my P133 machine but I wanted to make sure that I can "slow" it down for the more speed sensitive games,
I'm kind of new to all of this as it was my dad that messed with my DOS machine 33 or more years ago, I've been scouring the forum and the internet and the information is plenty, plenty enough to get lost and not knowing what to actually do. 😀
I'm using a Gigabyte ga-586stx motherboard with 32mb RAM and a S3 Trio v2 GPU,
Can I use setmul with this CPU? What else can I "tinker" to slow it down?
Thanks a lot for all your patience and help that you've given me on my numerous topics.

Reply 1 of 4, by bloodem

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You can use setmul to disable L1 cache, but as far as I remember, the undocumented test registers ( L1 code cache, L1 data cache, branch prediction, etc) specific to Pentium MMX don't work with a regular Pentium.
If you disable L1 cache (while keeping external cache enabled), you should get a ~ 486DX-33 equivalent speed. If you also disable the external cache (in BIOS), you'll get a slow 386 equivalent speed.

This should be enough to get good performance with most speed sensitive games.

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Reply 2 of 4, by daeds

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bloodem wrote on 2026-04-06, 12:14:

You can use setmul to disable L1 cache, but as far as I remember, the undocumented test registers ( L1 code cache, L1 data cache, branch prediction, etc) specific to Pentium MMX don't work with a regular Pentium.
If you disable L1 cache (while keeping external cache enabled), you should get a ~ 486DX-33 equivalent speed. If you also disable the external cache (in BIOS), you'll get a slow 386 equivalent speed.

This should be enough to get good performance with most speed sensitive games.

Oh, I'm good then! Good stuff.
Will I be able to venture forth in Britannia with this CPU then? Ultima's are always a pain.

Reply 3 of 4, by Shponglefan

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Aside from L1 and L2 cache disabling, there isn't much you can set on Pentium. There are some tools that employ software means of slow down (Slomo MoSlo I believe?).

Regarding Ultima games, if you are playing Ultima VII that game is notorious for re-enabling L1 cache even if it's been disabled.

So YMMV.

Last edited by Shponglefan on 2026-04-06, 16:50. Edited 2 times in total.

Pentium 4 Multi-OS Build
486 DX4-100 with 6 sound cards
486 DX-33 with 5 sound cards

Reply 4 of 4, by daeds

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Shponglefan wrote on 2026-04-06, 12:48:

Aside from L1 and L2 cache disabling, there isn't much you can set on Pentium. There are some tools that employ software means of slow down (Slomo I believe?).

Regarding Ultima games, if you are playing Ultima VII that game is notorious for re-enabling L1 cache even if it's been disabled.

So YMMV.

Yeah, I've battled more to get ingame and stable than actual ingame combat. It's part of the fun I guess. 😀

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