Path: utzoo!attcan!uunet!husc6!mailrus!tut.cis.ohio-state.edu!osu-cis!killer!elg From: elg@killer.UUCP (Eric Green) Newsgroups: comp.sys.amiga Subject: Re: Amiga UNIX Message-ID: <4585@killer.UUCP> Date: 25 Jun 88 06:10:22 GMT References: <8806212043.AA00625@cory.Berkeley.EDU> Organization: The Unix(R) Connection, Dallas, Texas Lines: 33 In message <8806212043.AA00625@cory.Berkeley.EDU>, dillon@CORY.BERKELEY.EDU (Matt Dillon) says: >>If you wanted to restrict your 68000 system in the same way as the 80x86, >>to 64K segments, you could allow only register relative code to be used. >>This would give you a fork that's just as good as any on the 80x86 machines. > Which you can do ... make all pointers 16 bit integers and then >whenever you make a pointer reference offset it by A4 (or whatever). >But frankly, this would cause more harm than good and be awefully slow! Actually, using 16-bit relative addressing is FASTER, on a 68000, than full 32-bit direct addressing. Don't believe me? Go look at the cycle count in your 68000 assembler manual. There's a reason the Manx compiler has a "small" model, and that's it. Manx doesn't extend that paridigm to the heap, however, as an Amiga Unix would have to do, because of the 32-bit pointers used by Amiga OS etc. > More harm than good, because all those standard Amiga structures >use normal 32 bit pointers, and one is bound to have a couple of them lying >around! If one is implementing a Unix operating system on the Amiga, why in the world would you want to have a couple of 32-bit pointers to AmigaDos hanging around? No, the primary argument is simply that most modern Unix programs will not fit in a 64K address space, and thus Unix on a 68000 sans MMU could never be more than a toy. -- Eric Lee Green ..!{ames,decwrl,mit-eddie,osu-cis}!killer!elg Snail Mail P.O. Box 92191 Lafayette, LA 70509 "Is a dream a lie if it don't come true, or is it something worse?"