Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!aplcen!uunet!mcsun!ukc!acorn!moncam!Elbereth From: Elbereth@moncam.co.uk (Dave Emmerson) Newsgroups: comp.sys.ibm.pc Subject: Re: 640K limit Message-ID: <604@marvin.moncam.co.uk> Date: 25 Feb 90 13:32:25 GMT References: <403@marvin.moncam.co.uk> Organization: Monotype ADG, Cambridge, UK Lines: 44 In article , writes: > emmo@moncam.co.uk (Dave Emmerson) writes: > > > Which other 2nd/3rd/4th generation processor has this b****y stupid > > 'protected' mode? > > [deleted] > So basically what it comes down to is that Motorola is working with > design ideas that are about 6 years younger than Intel's. But what > would happen if, say, the world turned to 64-bit microprocessors? > Motorola's 32-bit linear address space couldn't be retained without > (you guessed it) something resembling Intel segmentation. The > newer Intel processors would be in pretty much the same boat, even > in protected mode, for the same reasons. > [more deletions] I generally agree with most of the article, but the above extract just doesn't hold water. 64 bit processors have been around for some time btw, ask AMD. A 64 bit register/address 68xx0 would cope very easily with all current software without ANY extra mode instructions being needed. If you are familiar with 680x0 assembler, consider what happens when you do a 16 bit load into an address register. The MSB automatically gets extended into the upper 16 bits, right? So, literally all that's needed is for 32bit loads into 64bit address registers to follow the precedent. Such a powerful processor would in any case very likely have more registers than its predecessors, so while that mode is applied to the bottom 8 A & D regs, the new ones would be true 64 bit registers AF..8 and DF..8 to give new programmes access to the processor's real power. This is all speculation of course, the *facts* I have had from MOT are covered by a non-disclosure agreement, and cover a different aspect entirely, but I can tell you that the 680x0 is only in its infancy, even now, unless they eventually kill it off to promote the 88xxx, and that won't be for a while yet, the 88xxx isn't well enough established. If you're *really* interested, try to wangle an invite to one of the seminars, it can be quite enlightening, and gives you some idea which way things are going in the next few years. ATB Dave E.