OS-s versus Compilers

[fredvc $#at#$ esvax.dnet.dupont.com]

A cautionary comment on this response.
 >>Regarding Doug Smith concerns on the use of VMS I would like
 >>to add that we have a group of VAX 8600 where programs
 >>run about 200 times slower than on cray ymp. We understood they
 >>should run 30-50 times slower considering the speed and vector
 >>capabilities of the ymp. We suspect it is a problem of VMS
 >>I would appreciate any comments on the conversion to ULTRIX
 (1) 8600's are not very fast VAXen.  We found that speed doubled on going from
     a 8600 to an 8650, with more "juice" from an 8800 and a little
 more from
     a 6000-400.
 (2) CRAY Y-MP speed comes from several places: (a) a fast clock; (b)
     direct access to memory, rather than cache architecture; (c) very good
     SCALAR optimization; (d) Vector operations as an integral part of the
     system, rather as an add-on, along with good compiler recognition of
     vectorization opportunities.
 (3) The scalar/vector stuff (2c, 2d) is realized via the COMPILER, rather than
     the operating system, per se.
 There may be good reasons for converting from VMS to ULTRIX, but I would not
 place performance high on that list.  Unless you can get a better compiler in
 the deal, I would expect things to be pretty much the same.
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