Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!apple!amdahl!sbf10 From: sbf10@uts.amdahl.com (Samuel Fuller) Newsgroups: comp.arch Subject: Re: 64-bit addresses Message-ID: Date: 3 Mar 90 00:51:25 GMT References: <1786@gannet.cl.cam.ac.uk> Reply-To: sbf10@amdahl.uts.amdahl.com (Samuel Fuller) Organization: Amdahl Corporation, Sunnyvale CA Lines: 34 In article <1786@gannet.cl.cam.ac.uk> cet1@cl.cam.ac.uk (C.E. Thompson) writes: >On IBM 3090s (probably the mainframe that the previous poster had in mind) >"expanded storage" is RAM which is not directly addressable, but is moved >in 4Kbyte chunks to and from directly addressable storage by synchronous >instructions. It is used by MVS and VM as a very-high-speed paging device; >microcode assists can do the transfers without a software page fault in >some circumstances. > >If someone would like to explain what the economic advantages are to >providing extra storage in this form, I would be interested to listen. Expanded storage is used because it is much faster than disk for paging operations, and cheaper than mainstore for normal data storage. On most mainframes the mainstore is built out of ECC protected static rams. Expanded storage, is still ECC protected (I think) but is built out of slower, cheaper dynamic ram. Current mainframes have not yet found it necessary to implement an entire 2Gigabyte physical mainstore. Building such an array out of high speed static rams is still too expensive even for mainframes. The lower cost workaround is to provide expanded storage to be used as swap or paging or data space (at the OS's discretion). This has proven to be faster than using disk and cheaper than building all of the memory out of sram. -- --------------------------------------------------------------------------- Sam Fuller / Amdahl System Performance Architecture I speak for myself, from the brown hills of San Jose. UUCP: {ames,decwrl,uunet}!amdahl!sbf10 | USPS: 1250 E. Arques Ave (M/S 139) INTERNET: sbf10@amdahl.com | P.O. Box 3470 PHONE: (408) 746-8927 | Sunnyvale, CA 94088-3470 ---------------------------------------------------------------------------