Xref: utzoo comp.sys.mac.hardware:4250 comp.sys.mac.misc:1081 Path: utzoo!attcan!uunet!decwrl!apple!daveo From: daveo@Apple.COM (David M. O'Rourke) Newsgroups: comp.sys.mac.hardware,comp.sys.mac.misc Subject: Re: Addressable memory of 68000 (was Re: New Macs) Message-ID: <42706@apple.Apple.COM> Date: 6 Jul 90 17:28:17 GMT References: <90178.172523KPURCELL@LIVERPOOL.AC.UK> <268ACACA.44FD@intercon.com> <316@opusc.CS.SCAROLINA.EDU> <1990Jul4.003731.336@hellgate.utah.edu> <26708@netnews.upenn.edu> <42651@apple.Apple.COM> <1990Jul5.204534.14336@efi.com> Organization: Apple Computer Inc, Cupertino, CA Lines: 25 tim@efi.com (Tim Maroney) writes: >Couldn't you do a software fix? At startup, tweak the MultiFinder >pseudo-heap so that the ROM space is marked as allocated? This would >fragment the MF heap, of course, but it seems as if it would allow the >memory above the ROM to be used with only a small change in software. >Naturally, no applications could straddle the gap, given the Memory >manager limitations. For more information on this topic you can see pages 200-204 in "Technical Introducation to the Macintosh Family." Althought that suggestion would work if all we had to contend with was the ROMs. But the 680x0 family is a memory mapped processor so the orginal Mac HW design put the SCC in $80,000 page, and the IWM and VIA are in the last $C0,000 page. So above rom you have 2 4 meg pages for I/O devices and such. It's unclear from the documentation as to why these address spaces are so large, and if we actually need them to be that large. But for now that's the way the hardware likes it, and I'm not sure it's a simply software fix to change this memory map design. Hope this helps. -- daveo@apple.com David M. O'Rourke _______________________________________________________________________________ I do not speak for Apple in *ANY* official capacity.