Larry, I think I can answer your question for you. There are about 8 different instructions (I think) that are included in the Pentium, but which are not supported in the 6x86. These include VME and 4MB paging, among others. These instructions are officially "not documented, and not supported", but that doesn't mean they are not used. In fact Intel gave the instructions for using them to both IBM and Microsnot. VME is used by both Windows NT and OS/2.
The 6x86 basically implements the 486 instruction set, and is really a Pentium speed 486. The fact that the 6x86 does not include instructions such as VME does cause a few minor compatibility issues. First of all, with OS/2, my understanding is that you must boot with a Pentium and insert the VME-Off command before inserting the 6x86.
Secondly, the 6x86 does not support the CPUID instruction. The problem as I understand it is that if the 6x86 responds that it is a Pentium, who knows what instructions the program might try to execute, including non-supported ones, so it doesn't tell it that it is a Pentium. Thus some programs use CPUID to check for the presence of a Pentium, and when one is not found, they refuse to run (e.g. Sonic the Hedgehog). Other programs like Win 95 simply report that the CPU is a 486 (running at 900 MHz, or something).
My understanding is that the M2 supports the full PPro instruction set, so I hope that this time around Cyrix will support VME, etc, and there will no longer be any compatibility issues, but we will all have to wait and see.
Hope this helps,
Carl |
