Hi, (up late due to insomnia) On Mon, Aug 26, 2013 at 3:22 PM, Jim Michaels <[email protected]> wrote: > > https://www-ssl.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html? > > these are the intel64 dev manuals. > enjoy.
FYI, I'm not a systems programmer, so most of this is overkill for me. I realize this is "freedos-devel", but I'm not sure how many of us here are really doing any active work in such an area. > I was trying to look up the limit register and see how big it was, and saw > this inetad talking about MS-DOS/win95 compatibility mode and how it does > things to the CPU that limit the CPU to one logical proc, and that's why > it's deprecated in newer OS's. > > interesting treatise. Your actual subject line says "read section 8.7.2, appendix D". You didn't mention which specific .PDF, but it appears to be "Intel 64 and IA-32 Architectures Software Developer's Manual Volume 1: Basic Architecture" (aka, 253665.pdf). And actually, what you're apparently referring to isn't DOS compatibility overall but instead an "MS-DOS specific" method of "x87 fpu exception handling". I'm not really savvy about it, but NE bit (CR0) must be 0 for DOS, apparently. This is because of legacy, originally having an optional (separate) 8087, hence IBM did things differently with their IBM PCs, before the 287 fpu itself added a newer way. Yet x87 fpus were often still sold separately until the Intel Pentium. And to make things even more complicated, now we have MMX+3dnow!, SSEs, and AVXs. Ugh. "That's why it's deprecated" ... I don't think it's that simple, even on a purely technical level (ignoring corporate politics). Here's what it says (D.4.3): "Note that the special DP (Dual Processing) mode for Pentium processors, and also the more general Intel MultiProcessor Specification for systems with multiple Pentium, P6 family, or Pentium 4 processors, support x87 FPU exception handling only in the native mode. Intel does not recommend using the MS-DOS compatibility mode for systems using more than one processor." But that apparently doesn't mean you can't emulate MS-DOS x87 compatibility mode in the (V86?) "virtual machine" while using x87 native mode (see D.3.6.4). ------------------------------------------------------------------------------ Introducing Performance Central, a new site from SourceForge and AppDynamics. Performance Central is your source for news, insights, analysis and resources for efficient Application Performance Management. Visit us today! http://pubads.g.doubleclick.net/gampad/clk?id=48897511&iu=/4140/ostg.clktrk _______________________________________________ Freedos-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/freedos-devel
