Xref: utzoo comp.os.misc:528 comp.os.cpm:1799 Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!agate!bionet!apple!rutgers!elbereth.rutgers.edu!ron.rutgers.edu!ron From: ron@ron.rutgers.edu (Ron Natalie) Newsgroups: comp.os.misc,comp.os.cpm Subject: Re: a very naive Question??? Message-ID: Date: 11 Oct 88 02:00:30 GMT References: <6693@ut-emx.UUCP> Organization: Rutgers Univ., New Brunswick, N.J. Lines: 25 The article is inaccurate. System V has virtual memory of almost any definition. Originally System V had problems with virtual memory. There are two differing definitions of Virtual Memory. The more liberal definition says that Virtual Memory provides for swap extension of real memory and some sort of address translation. UNIX has always done this. The more restrictive definition is that some mechanism such as paging or segmented swapping exists as well. The difference is summarized in the following. Suppose you have 1 M of real memory and you want to run a 2 M process. Prior to recent system V versions, you were out of luck. It always expected to load a whole process as a unit. On paging systems, it only needed to bring in the parts needed for the execution of the current instruction. The virtual memory argument was best summarized by Bruce Crabill of the University of Maryland. "It ain't virtual unless it's not all there." This means that the liberal definition is kind of weak if you have to have real memory to back your virtual memory for any give process. -Ron Of course, they may have meant VM as Virtual Machine. It is doubtful that anything other than AIX/370 is going to support that.