Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!henry From: henry@utzoo.UUCP (Henry Spencer) Newsgroups: net.micro,net.arch Subject: Re: 386 Family Products Message-ID: <6129@utzoo.UUCP> Date: Sat, 9-Nov-85 19:37:17 EST Article-I.D.: utzoo.6129 Posted: Sat Nov 9 19:37:17 1985 Date-Received: Sat, 9-Nov-85 19:37:17 EST References: <129@intelca.UUCP> <392@aum.UUCP> <225@l5.uucp> Organization: U of Toronto Zoology Lines: 17 > ... if I understand the Intel literature correctly, you > can do paging on top of emulating the 8086 in "virtual 86 mode." Then > you can set the page(s) where the screen is to "not present," and then do > a trap every time it is accessed. Alternatively, you could set that page > as "read-only," so that you would do a trap only on writes. According to > Intel, this is not as fast as one might like... "not as fast as one might like" is the understatement of the century, actually. This is a serious performance problem in virtual-machine work when the machine has memory-mapped i/o devices. For the screen, you might be able to live with a scheme in which the system scanned the page table every 60th of a second to identify "screen" pages which had been modified, and then did something appropriate with them. Trapping every screen-update write is a performance disaster. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry