If the software makes use of the new instructions the Pentium bought in then it wont work on a 486 namely CPUID, CMPXCHG8B, RDTSC, RDMSR, WRMSR, RSM instructions. It could also fail if it doesn't find the the new FPU the P5 has and relies on it to function.

The other case would be if the software needs MMX instructions, IIRC there were Pentium MMX Overdrives, not sure they were ever compatible with anything other than socket 5/7 however.

Some software also simply looked for the CPUID instruction and if its wasn't present then it either gave an error message or simply failed to run.

Trashbytes wrote on 2024-02-15, 23:21:

It could also fail if it doesn't find the the new FPU the P5 has and relies on it to function.

I thought that'd just make the game run slow and not prevent it from running. Do you know examples I could test?

eddman wrote on 2024-02-15, 23:35:

Trashbytes wrote on 2024-02-15, 23:21:

It could also fail if it doesn't find the the new FPU the P5 has and relies on it to function.

I thought that'd just make the game run slow and not prevent it from running. Do you know examples I could test?

If the program doesn't check the CPUID then yes it may just run slower or run but with issues, if it does some basic sanity checking then it would simply fail to run and give you an error when executing.

https://en.wikipedia.org/wiki/Pentium_(original)

Describes some of the core changes the Pentium made, the FPU was one of the biggest changes.

Yea, I had already read that page but thought games didn't care about those changes when it comes to basic compatibility. Even games from late 90s launch on a 486, so I didn't think there are some that don't. Another possibility from the example I posted in the OP is an emulation bug. Perhaps someone who owns that game can confirm.

The few that had strict Pentium checks were probably either 1997 "MMX" games (sweet intel money) or those that didn't realize there were other 5th/6th gen processors that don't satisfy Pentium checks so they're taken out before shipping (i.e. MDK) or shipped anyway (i.e. Bug!). Minimum requirements stating "Pentium" is also thrown more as a shorthand for having a FPU rather than specifying 486DX2 ro 4 which most could actually run but that'll have a confuse with 486SX.

I remember trying to play a few dos game demo's from magazine CD's on my 486 and getting.
"This game requires at least a Pentium Processor" and dropping back to dos.

Can't really remember the games (as I couldn't play them so no memories) but I think Destruction Derby 2 may of and been disappointed (even though DD1 already struggled)

The Sims won't run on a 486.

Destruction Derby 2 won't install on a 486

Windows 95/Direct X is really a Pentium+ era. But were there really a pure DOS game that absolutely needed a real Pentium?

Cyberdyne wrote on 2024-02-19, 16:05:

Windows 95/Direct X is really a Pentium+ era. But were there really a pure DOS game that absolutely needed a real Pentium?

Destruction Derby 2 is a pure dos game, was released during that era when both a windows and dos version of the game was released.
https://www.mobygames.com/game/2546/destructi … -derby-2/specs/

Slam City with Scottie Pippen won't run on anything less than a Pentium CPU, game will give an error stating such.

thepirategamerboy12 wrote on 2024-02-21, 02:58:

Slam City with Scottie Pippen won't run on anything less than a Pentium CPU, game will give an error stating such.

That's odd. On the box it says "25 MHz 486 processor or faster".

Perhaps a misprint.

I think there are DOS games which don't run a Pentium anymore. Or a late 486DX4.
They're making use of undocumented 486 instructions, which are merely present in the original 486 chip design(s).
That's what I heard, at least. One strategic flight simulator was affected, I vaguely remember.

eddman wrote on 2024-02-21, 09:15:

thepirategamerboy12 wrote on 2024-02-21, 02:58:

Slam City with Scottie Pippen won't run on anything less than a Pentium CPU, game will give an error stating such.

That's odd. On the box it says "25 MHz 486 processor or faster".

Perhaps a misprint.

Just tried it again myself to be sure and this is what happens: