Path: utzoo!attcan!uunet!husc6!cmcl2!adm!smoke!gwyn From: gwyn@smoke.ARPA (Doug Gwyn ) Newsgroups: comp.unix.questions Subject: Re: BSD vs. System V, one last thing... Message-ID: <8525@smoke.ARPA> Date: 18 Sep 88 02:21:04 GMT References: <553@umbio.MIAMI.EDU> <21106@cornell.UUCP> Reply-To: gwyn@brl.arpa (Doug Gwyn (VLD/VMB) ) Organization: Ballistic Research Lab (BRL), APG, MD. Lines: 28 In article <21106@cornell.UUCP> murthy@cs.cornell.edu (Chet Murthy) writes: >Actually, v7 didn't have virtual memory built-in. >At least, not paged virtual memory. sysV diesn't >have it because, as I heard it, it is derived from >PWB/UNIX, and not v7. PWB was the same UNIX, >so I have heard, that spawned 32v, which went on to >become 2bsd, 3bsd, 4bsd, etc. However, sysV did >get paging in version V.2.2. And also in V.3 >System V did indeed have swapping, though. But >then swapping can be done with a minimum of hardware. This is mostly wrong. UNIX/32V sprang directly from 7th Edition UNIX. UNIX System V has resulted from several evolutionary streams, not especially PWB. The original PWB/UNIX and 7th Edition UNIX had essentially the same memory management (swapping) strategy anyway. The PDP-11 had sufficient hardware (KT11) for demand paging. (It was missing page reference bits, but so was the VAX-11/780.) You have to be careful with UNIX System V version numbers. Release 2 Version 2 for the 3B2. for example, did NOT implement demand paging (that occurred with Release 2 Version 4 for 3B2). I don't think there was a Release 2.2 for any architecture, but there was a Release 2.1 for the 3B2. UNIX System V used a partial-swapping strategy on most architectures until the demand-paging versions came out. Most implementations of UNIX have some form of swapping, even if they also provide demand paging.