OC.CIVIL@CU20B.COLUMBIA.EDU (Holt Farley) (09/03/87)
We are considering replacing our VAX 11/750 CPU with a 11/780 which we can get VERY cheaply from another department here at Columbia Univ. This machine will run VMS, and is used to support faculity/graduate research in an engineering department. We do quite a bit of program development as well as run many programs that use a lot of system resources: finite element routines (large matrices), symbolic languages (MACSYMA, SMP), TeX, etc. My question is: What kind of performance increase will we likely see if we do purchase the 780? Obviously, the answer to this question depends upon the exact configuration of the computers and the work done. Our 750 currently has 8Mb of memory and can only support 10-12 typical users before response time gets really terrible. NULL mode is extremely rare! I expect one of the main advantages to the 780 is that I can install lots of memory --- I plan to put at least 16-20 Mb in the 780. So, if you have experience in a similar work environment and have used both 750's and 780's, I would very much like to hear your comments. Alternate ways to improve performance are also welcomed --- please keep in mind that this machine must run VMS and the $ amount must be low! Thanks for your help. Holt Farley Columbia Univ. Civil Engineering system@cucevx (Bitnet) oc.civil@cu20b.columbia.edu (Internet) -------
d2b@rayssd.RAY.COM (Donald A. Borsay) (09/16/87)
In article <12331690952.196.OC.CIVIL@CU20B.COLUMBIA.EDU> OC.CIVIL@CU20B.COLUMBIA.EDU (Holt Farley) questions the performance gains of upgrading from a 750 to a 780, when operating in a engineering environment. Holt points out that the current 750 has 8mb of memory and the proposed 780 would have 16-20mb. In a program development environment, memory is the highest demand. The linker, for one, is a big hog. The run-time environment for some of the applications you describe (finite element and symbolic langauges) most likely contribute to your lack of CPU time. Doubling your memory will help alot (need hard parameter values and fault rates to guess at how much). Since a 750 is 60% of a 780, the CPU upgrade should give you a net increace of 66% in CPU resouces. The one configuration option you do not mention is the Floating Point Accelerator. In your environment, I would strongly urge you to have one. Hope this helps. -- Don |Raytheon Company, Submarine Signal Division, Portsmouth, RI Borsay |ARPAnet: d2b%rayssd.RAY.COM@a.cs.uiuc.edu |UUCPmail: {allegra, decvax!brunix, linus!raybed2}!rayssd!d2b
bob@uhmanoa.UUCP (Bob Cunningham) (09/17/87)
If you already have an FPA on the 750, don't expect much more throughput for compute-intensive jobs. The 780 and 750 FPAs have very similar performance. I.e., for pure "number crunching" programs that use exclusively or primarily floating point, a 780 is only perhaps 10% faster than a 750. -- Bob Cunningham bob@hig.hawaii.edu