Path: utzoo!mnetor!uunet!cbmvax!snark!eric From: eric@snark.UUCP (Eric S. Raymond) Newsgroups: comp.arch Subject: Re: Is the Intel memory model safe from NO-ONE ?!? Message-ID: <22830abd:a11@snark.UUCP> Date: 7 May 88 13:01:14 GMT References: <1806@obiwan.mips.COM> <2904@omepd> <353@cf-cm.UUCP> Organization: ill Lines: 28 Summary: Since when does segmentation = memory protection??? In article <2411@louie.udel.EDU>, rminnich@udel.EDU (Ron Minnich) writes: > But having used segmented machines (done right, at Burroughs) and > non-segmented machines, i can say that i trust programs running > on segmented machines a whole lot more. And I trust C programs > running on non-segmented machines not-a-whit- just ask anybody > who knows about NULL pointers. Waaaait a second, here. It sounds to me like two very different issues are being confused. Let's have some definitions: Segmented architecture -- one in which the register width is not sufficient to address all of memory, so that full addresses must be base/offset or segment-descriptor/address pairs. Memory protection -- the ability to enforce memory addressing restrictions on execution threads so that references outside a 'legal' region are detected and trapped (in UNIX terms, raise a SIGSEGV). These are very different concepts. To trap NULL pointers you want memory protection. Segmentation implies a crude form of memory protection, with fixed-sized regions defined by the address span of an offset. But the two should not be confused. -- Eric S. Raymond (the mad mastermind of TMN-Netnews) UUCP: {{uunet,rutgers,ihnp4}!cbmvax,rutgers!vu-vlsi,att}!snark!eric Post: 22 South Warren Avenue, Malvern, PA 19355 Phone: (215)-296-5718