Path: utzoo!attcan!uunet!sco!seanf From: seanf@sco.COM (Sean Fagan) Newsgroups: comp.arch Subject: Re: 386 machines are workstations? Message-ID: <6391@scolex.sco.COM> Date: 28 May 90 00:38:55 GMT References: <6363@scolex.sco.COM> Sender: news@sco.COM Reply-To: seanf@sco.COM (Sean Fagan) Organization: The Santa Cruz Operation, Inc. Lines: 47 In article peter@ficc.ferranti.com (Peter da Silva) writes: >In article <6363@scolex.sco.COM> seanf@sco.COM (Sean Fagan) writes: >> In article meissner@osf.org (Michael Meissner) writes: >> >But this is all invisable at the user level. The new mode is in >> >kernel space. As long as you treat all pointers as 32-bit quanities, >> So a user can't do something like >> movl (0xabcddead),r0 >You're usually a pretty cool dude, Sean. Thank you. 8-) >Why are you suddenly going into >hair-splitting mode here? In practical terms, machines like the 68000 and >the 32000 are compatible across the board. Practically, yes. And so are the 68ks. *However*: if I were writing an assembler for the 32532, and wanted to do it quickly, and not worry overmuch about memory overhead, I would do all addresses as 32-bit absolute (or 31-bit relative, whatever). The code thus generated would *not* run on a 32016, but *would* run in user mode on a '532. An incompatability caused by NS's original design. (Personally, I don't really think it's a problem. But since the goal of usenet is to split hairs, ... 8-)) >The 80x86 is a whole different ball of wax, because earlier processors >are emulated rather than being a subset of the new one. Running old code >instead of recompiling causes severe performance degradation. Hair-splitting time *again* 8-): the 80286 is not emulated on a '386. That is, the processor executs the instructions directly, and has a 16-bit mode on it's ALU (so I've been lead to believe. I think only intel knows for sure). Otherwise, a 32-bit add would be quicker than a 16-bit add, and it's not. (However, it *can* be argued that, if the 16-bit mode were not there, the 32-bit add *would* be faster. Depends on how the chip was designed.) And, of course, old code *can* run on the *86 processors. You don't have to recompile. You don't get the new features, that's true, but I really don't know of any processor that you *do* (other than, more address bits but that was more due to a limitation of the original processor [i.e., the 68k had 32-bit address registers, but only 24 of them mattered] than to a superiority in the method). -- -----------------+ Sean Eric Fagan | "It's a pity the universe doesn't use [a] segmented seanf@sco.COM | architecture with a protected mode." uunet!sco!seanf | -- Rich Cook, _Wizard's Bane_ (408) 458-1422 | Any opinions expressed are my own, not my employers'.