Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!asuvax!mcdphx!udc!chant!aglew From: aglew@urbana.mcd.mot.com (Andy-Krazy-Glew) Newsgroups: comp.arch Subject: Re: SCSI on steroids, mainframes move over Message-ID: Date: 24 Aug 89 19:32:32 GMT References: <5932@pt.cs.cmu.edu> Sender: aglew@urbana.mcd.mot.com Organization: Work: Motorola MCD, Urbana Design Center; School: University of Illinois at Urbana-Champaign Lines: 30 In-reply-to: butcher@g.gp.cs.cmu.edu's message of 22 Aug 89 06:40:56 GMT >The biggest, fastest business computers seem to run 1960's operating systems >without protection, and allow user programs to do I/O without OS assistance. >My new question. Is fast I/O all that micros need to bury mainframes? Or >is user level I/O needed? If needed, how can simple hardware be built which >allows direct user level DMA I/O? Gould NPL's UIOM (Universal I/O Module) had a feature whereby it understood page tables, so could be told to do I/O into such-and-such a virtual map. Unfortunately, virtual I/O was seldom used because the UIOM had no TLB, and so virtual I/O was slow. From virtual I/O, it is a small step to direct user level I/O: the user needs some way of saying "Start my I/O now please, using the command packet that I've placed at address so-and-so". Note that memory mapping device control registers into user memory is unacceptable, because you don't want the user intefering with other users' I/O, unless you have one user per device (conceivable for displays and ttys; not acceptable for disks in a UNIX environment). One of the Japanese super-IBM-compatibles (I think that it was Hitachi) had a paper a while back on direct emulation of I/O instructions in a virtual machine --- required the virtual machine to be in contiguous physical memory, and a base and bounds register loaded into the channel controller. -- Andy "Krazy" Glew, Motorola MCD, aglew@urbana.mcd.mot.com 1101 E. University, Urbana, IL 61801, USA. {uunet!,}uiucuxc!udc!aglew My opinions are my own; I indicate my company only so that the reader may account for any possible bias I may have towards our products.