Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!wuarchive!udel!haven!ncifcrf!lhc!usenet From: usenet@nlm.nih.gov (usenet news poster) Newsgroups: comp.arch Subject: Re: 64 bits Message-ID: <1990Aug17.215527.5822@nlm.nih.gov> Date: 17 Aug 90 21:55:27 GMT References: <5539@darkstar.ucsc.edu> <13285@yunexus.YorkU.CA> <30728@super.ORG> <9660@ganymede.inmos.co.uk> <224@csinc.UUCP> Reply-To: states@tech.NLM.NIH.GOV (David States) Organization: National Library of Medicine, Bethesda, Md. Lines: 29 gadbois@cs.utexas.edu writes: > I have noted this before, but it probably bears repeating: While big > address spaces are certainly desirable, don't forget that we are > talking about powers of 2 here. Assuming that media for backing store > costs $1.00 per megabyte, enough to support a full 64-bit address > space would set you back $17,592,186,044,416.00. A 48-bit space at > those rates would cost $268,435,456.00, and even a measly 40-bit (just > one terabyte) one is over a million bucks. Media costs are going to > have to drop a lot for really big address spaces to be practical. Sure for physical memory and we are all spoiled by workstations with enough RAM that nothing ever page faults anymore (:-), but DEC started shipping VAXes with 128k of RAM, a 70 MB disk and a 4GB virtual address space (and it *did* page fault). Virtual space > physical space can be useful for some problems. With very high speed optical communications coming on line, the concept of a site wide address space could make sense. In setting up such a system you would almost certainly want physical addresses to be quite sparse ("Sorry, you can't add a disk to that machine without spliting addresses or reconfiguring the whole thing in a bigger slot..."). We currently have about 40GB of text data online on various machines, and I certainly wouldn't mind having it all byte addressable. You could do it in 48 bits, but is it really going to save you that much compared to going straight to 64? > --David Gadbois David States