CLAYTON@XRT.UPENN.EDU ("Clayton, Paul D.") (09/10/87)
Information From TSO Financial - The Saga Continues... Chapter 21 - September 9, 1987 Holt Farley from Columbia Univ. Civil Engineering has asked the following question. 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. RESPONSE: I have read various articles about MIP ratings between the various CPU types and the bottom line is that the 750 and 780 and not that far apart, maybe less then .2 MIPS. This is not alot by itself. Both systems can have a UNIBUS on them and they will handle the same amount of traffic, give or take a little. The next major difference is the CMI interface on the 750 versus the MASSBUS on the 780/785/86. The CMI is a VERY clean and efficient means of passing information and from the 750 system I used to run speed tests on, it came close to the MASSBUS throughput. The BIGGEST advantage is MEMORY, and you said that 16-20 MB is what you are shooting for. I would not stop at 20MB. The 780 memory is VERY CHEAP and available. I just bought some 785 memory that with a trade in allowance on the original 1MB boards it coast me $850 per 4MB board. As a school you could probably get it cheaper as a right off for some system clearing house. I would go for as much memory as possible and cut down on PAGING and SWAPPING. The extra .2 MIPS may make a BIG difference as long as it is NOT spent in system space doing paging and swapping. Adjustments of working set values in the UAF records would also be advisable to make the best use of the additional memory. I would also recommend the addition of the Floating Point Accelator card set to help with the number crunching. It also helps to a certain extent in VMS doing other tasks. Bottom line. Get the 780, with the MOST memory possible and consider adding the FPA to the processor. Good luck.. :-) Paul D. Clayton - Manager Of Systems TSO Financial - Horsham, Pa. USA Address - CLAYTON%XRT@CIS.UPENN.EDU