Jeff Walther wrote: > > On Nov 25, 9:32 pm, tortoise <[email protected]> wrote: > >> And BTW there was also a separate MMU chip for earlier MMU-less 68k (? >> '020?) > > The Macintosh II had a 68020 with an AMU (?) (IIRC) chip which could > be updated to the PMMU.
I believe that Apple referred to their ASIC replacement for the PMU as an HMMU. > > My understanding is the the 68K emulator built into the PPC Macintosh > ROMs emulates a 68020. So the hooks for this kind of system must > still be in the operating system at that time. The thing that > surprises me is that the OS could detect a 68040 and then use the > 68020 system in which a PMMU may be absent. Perhaps if the OS does > not detect a PMMU it assumes it is running on a 68020 or earlier? It > would all depend on how Apple built those case statements (or > equivalent). The existence of an MMU is only going to be of concern to an OS and (just guessing) an emulator is probably not going to deal with it at all. The emulator would just let the native OS it's running under deal with memory. IIRC the 68030 had no user level code differences with the 68020. The 68040 had a few but very few programs made use of them in order to maintain code compatibility with older computers. So emulating a 68020 would work with most apps. -- Clark Martin Redwood City, CA, USA Macintosh / Internet Consulting "I'm a designated driver on the Information Super Highway" -- ----- You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/
