Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site sjuvax.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!sjuvax!jss From: jss@sjuvax.UUCP (J. Shapiro) Newsgroups: net.arch,net.micro.16k,net.micro.68k Subject: Re: 24 bit vs. 32 bit address space Message-ID: <927@sjuvax.UUCP> Date: Thu, 7-Mar-85 20:41:44 EST Article-I.D.: sjuvax.927 Posted: Thu Mar 7 20:41:44 1985 Date-Received: Mon, 11-Mar-85 11:13:21 EST References: <983@watdcsu.UUCP> <2385@nsc.UUCP> <730@amdcad.UUCP> Organization: Saint Josephs Univ. Phila., Pa. Lines: 21 Xref: watmath net.arch:939 net.micro.16k:257 net.micro.68k:644 [Pacman's revenge...] It has been suggested that with the MMU, the 320xx chips allow 32 Mbytes of process space. This is true, but misleading. The A24 line is determined by a bit set in the MMU, and unless the operating system provides you with the ability to set that bit (it is intended for supervisor address space protection), you are out of luck... Also, unless you do some funky stuff with the page tables, setting that bit will suddenly cause the processor to have trouble finding your code... The right answer to 32 bits is to use the 68020 or 68012 if your need is immediate. Also, check out the NCR/32 series. If your need is less immediate, hold off until the 32532 appears. It looks as though that will prove a very interesting chip. In the meantime, I can think of many things I can do 24 bits that I can't do on a Macintosh. I can also think of things I can't do on a VAX unless it is in single user mode.... Jon Shapiro Haverford College