Path: utzoo!utgpu!water!watmath!clyde!rutgers!mit-eddie!zrm From: zrm@eddie.MIT.EDU (Zigurd R. Mednieks) Newsgroups: comp.sys.mac Subject: Re: Is Mac II flawed? Keywords: Nubus architecture Message-ID: <7630@eddie.MIT.EDU> Date: 10 Dec 87 20:23:22 GMT References:<952@uokmax.UUCP> Reply-To: zrm@eddie.MIT.EDU (Zigurd R. Mednieks) Organization: MIT, EE/CS Computer Facilities, Cambridge, MA Lines: 40 In article <952@uokmax.UUCP> jlperkin@uokmax.UUCP () writes: I have been told about an article appearing in MacUser a few months ago stating that there was a problem with the Nubus... .... According to thissource the rom placement makes this impossible because of the downward compatibility of the Mac II with the SE. Therefore it would take a complete motherboardchange to correct the problem. In other words, big bucks! It also means you ... > > >J. Les Perkins The Mac II motherboard is a virtual NuBus slot, but that should not stand in the way of an upgrade board "mapping in" the Mac II ROMs, or more likely, copying them into faster memory. Motherboard assets like the SCSI and seriial ports could also be mapped into any addressing scheme from any NuBus slot. The SE compatibility mode consists of making each NuBus slot a 1MB partition in a 16MB SE-like address space. Why they bothered with this, I don't really know, since no reasonable application really cares about anything outside the application heap, nor even where the application heap is. This makes life tough for high-end (e.g. 24-bit) graphics cards because there isn't enough address space in each slot under this mapping scheme. (Hey Apple, any good answers for this seemingly backward-thinking design decision? And what about future MacII OSs? Will they have full 32-bit NuBus addressing for Mac NuBus peripherals?) None of this, however, nixes the idea of a NuBus upgrade card for a 68030 or other future processor. Nor is a multiprocessor setup out of the question. In fact, a separate NuBus processor would not have to limit itself to the 1MB per card addressing scheme of the current Mac OS. -Zigurd -- ------------------------------------------------------------------------ Zigurd Mednieks MURSU Corporation (617)424-0146 25 Exeter Street Boston, MA 02116