Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site wdl1.UUCP Path: utzoo!watmath!clyde!cbosgd!ihnp4!zehntel!dual!amdcad!fortune!wdl1!jbn From: jbn@wdl1.UUCP Newsgroups: net.unix-wizards Subject: Re: VM/370 security and performance Message-ID: <192@wdl1.UUCP> Date: Tue, 15-Jan-85 16:42:43 EST Article-I.D.: wdl1.192 Posted: Tue Jan 15 16:42:43 1985 Date-Received: Sun, 20-Jan-85 06:21:04 EST Sender: jrb@wdl1.UUCP Organization: Ford Aerospace, Western Development Laboratories Lines: 16 Nf-ID: #R:brl-tgr:-662300:wdl1:17100044:000:955 Nf-From: wdl1!jbn Dec 20 20:30:00 1984 No, that's the beauty of VM; VM WILL RUN UNDER VM! It is actually possible, strange though it may sound to the UNIX community, to run a full-fledged operating system, interrupt handlers, device drivers, page table updating and all, UNDER THE CONTROL OF THE OPERATING SYSTEM. There's a substantial performance penalty, but it's on the order of 30%, not 300%. So operating system development takes place along with other work. This technology was first developed for the IBM 360/67; a certain amount of special hardware support is needed to make it work, but less than one might think. The key idea is that it must be possible to simulate correctly all privileged operations. Incidentally, operating systems of this type are called ``hypervisors''. Few kinds of CPUs are capable of supporting a hypervisor, but all 370s, 43xxs, and 303xs can do so. And yes, you can run VM under VM under VM ..., losing 30% performance with each layer.