Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site cornell.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!harvard!talcott!panda!genrad!decvax!bellcore!allegra!ulysses!mhuxr!mhuxt!houxm!vax135!cornell!jqj From: jqj@cornell.UUCP Newsgroups: net.unix-wizards Subject: MicroVAX II performance? Message-ID: <1886@cornell.UUCP> Date: Tue, 21-May-85 05:55:28 EDT Article-I.D.: cornell.1886 Posted: Tue May 21 05:55:28 1985 Date-Received: Fri, 24-May-85 07:36:46 EDT Sender: jqj@cornell.UUCP Organization: Cornell Univ. CS Dept. Lines: 49 From: jqj (J Q Johnson) To reiterate a request that has already appeared on Unix Wizards, can anyone out there provide information on MicroVAX II performance with multiple users under Unix? Granted, the MV II is a fast, nifty machine for a small number (1 to 3?) of users; can it replace a 780 (750?) for ordinary timesharing? It certainly won't replace my 780 with 2GB of disk and 40 to 50 users (at least not this year), but how would it perform in a configuration with, say, 5MB memory, 5 RD53 disks, and 12 simultaneous timesharing users? Some issues: The RD53 is a fairly slow disk (RD52 is too slow to even consider in this context). The controller for A-series disks won't be available till late this year (or, more likely, early next year). Will lots of spindles make up for slower average access? Let's ignore the issue of whether 350MB is enough disk and simply worry about performance for a while. The MV II uses the Q bus for all I/O. Is this a potential bottleneck, particularly in an environment with moderately high Ethernet traffic competing for the bus? My experience with 780s seems to be that they are very happy to have their disks sitting on Massbus or SI controllers (or on a CI). If I were configuring a 780 with UDA-50, I think I'd want to hang it on a dedicated Unibus. Can I install a second Q bus on the MV II? How smart is the controller for the RD53? In a typical disk transfer, how much work does the CPU have to do compared, for example, to a UDA50? How wide is the DMA path from Qbus to memory? Unless memory deceives me, the VAX/750 has only 4 registers for controlling byte DMA transfers, which makes them a very scarce resource, especially if for speed your drivers want to dedicate one or two to each DMA device; 780 has 64, which is plenty. How many has the MV II? How big is the cache, and how fast is main memory? Floating point performance: I gather that the MV II supports G and H format fp numbers. How about D format? In hardware or in emulation? How fast? Note that binaries from existing C programs will do all their calculations in D format, so if D format is slow one would at least want to recompile using a compiler that generates G format; what does the distributed Ultrix C compiler use? What other potential bottlenecks exist in the MV II architecture?