Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/3/84; site talcott.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!harvard!talcott!tmb From: tmb@talcott.UUCP (Thomas M. Breuel) Newsgroups: net.arch,net.micro.16k,net.micro.68k Subject: Re: 24 bit vs. 32 bit address space Message-ID: <344@talcott.UUCP> Date: Sat, 9-Mar-85 15:24:14 EST Article-I.D.: talcott.344 Posted: Sat Mar 9 15:24:14 1985 Date-Received: Tue, 12-Mar-85 20:06:12 EST References: <983@watdcsu.UUCP> Organization: Harvard University Lines: 15 Xref: linus net.arch:748 net.micro.16k:234 net.micro.68k:580 > I hear Apple is using the top byte on the Macintosh addresses. Seems like > this is going to make it difficult for them to port their software to the > 68020. Seems to me that using the upper byte of a 68000 address is just I doubt that using the upper 8 bits will give problems in porting MacIntosh software: -- use of the upper 8bits is in most cases hidden in the ROM (i.e. most applications don't even know about it). -- the 68000 already uses all 32bits in address calculations. The only way you would have to modify the code using the upper 8bits is if you have more than 16M of memory or a memory management unit which objects to bits 24-31 being set. Thomas.