Path: utzoo!attcan!uunet!husc6!mailrus!ames!elroy!peregrine!spsd!dds From: dds@spsd.SPSD.DG.COM (Dennis D. Sherod) Newsgroups: comp.os.misc Subject: Re: DG/UX -- Seybold's Review ( long ) Message-ID: <943@spsd.SPSD.DG.COM> Date: 21 Sep 88 06:35:44 GMT References: <602@spsd.SPSD.DG.COM> <11590002@hpisoa1.HP.COM> Sender: news@spsd.SPSD.DG.COM Reply-To: dds@spsd.UUCP (FTP guest login) Organization: Data General SPSD Santa Ana, CA Lines: 45 In article <11590002@hpisoa1.HP.COM> vandys@hpisoa1.HP.COM (Andrew Valencia) writes: >/ hpisoa1:comp.os.misc / dds@spsd.SPSD.DG.COM (Dennis D. Sherod) / 7:02 pm Sep 11, 1988 / > >>DG needs to distinguish its approach to Virtual Memory Management from >>those used by both Hewlett-Packard and IBM. Both HP/UX and AIX allow >>for users to have transparent access to programs that do not fit into >>physical memory by swapping segments in and out of main memory. DG's >>approach allows users to have transparent access to programs that do >>not fit into physical memory by demand paging on a per page basis. DG >>needs to be clear on how its approach is superior to this alternative. > > Could you explain this statement? Our VM system is essentially the >BSD 4.2 VM system, with some modifications for performance and real-time >latency. Like 4.2, our system can swap out user processes. But it is also >perfectly capable of doing virtual paging. Doing only demand-paging >might be a win, but I'd be interested to hear in exactly what ways it >manifests itself for DG over a system like 4.2/4.3. I was not the author of the article. Recall that this was a reprint of a review made by a Patricia (think that's the name) Seybold publication. SIDEBAR: They do a number of industry product comparisons often at a vendor's request. I don't wish to second guess the author's intent here, and I am not that familiar with BSD's or HP's VM strategies, but as some general statements: Segment swapping is generally considered a process strategy while paging is a memory management strategy. There are also some connotations as to the size of the VM objects, segments being higher in the hierarchy and larger. By process strategy I mean, how the operating system views a process' intent on using CPU resources and decides to move parts or all of the process in and out of memory. While memory management strategy is often largely handled by hardware architecture and works with much smaller fixed size pieces 'pages'. I know I didn't answer your question, but since I'm not familiar with your VM architecture, I'm not even sure what the question is. If there is sufficient interest, I will prepare an article discussing in more detail DG/UX's VM architecture, but I can not carry on an intelligent discussion of alternate architectures and their merits. -- Dennis Sherod, Data General Corporation UUCP: ..!ucsd!spsd!dds Software Products & Services Division TELCON: +1 714 835 3583 1224-B Village Way,Santa Ana,CA 92705 Internet: dds@spsd.SPSD.DG.COM