Vax 11/780 performance vs Sun 4/280 performance

[Don Speck]

I am reminded of this article from comp.arch:

In article <44083 at beno.seismo.CSS.GOV>, rick at seismo.CSS.GOV (Rick Adams) writes:
> Well, to start with I've got a Vax 11/780 with 7 6250 bpi 125 ips
> tape drives on it. It performs adequately when they are all running.
> I STILL haven't found anything to replace it with for a reasonable amount
> of money. Nothing in the Sun price range can handle that I/O volume.

I've seen a PDP-11/70 with eight tape drives, too.

And as Barry Shein said, "An IBM mainframe is an awesome thing...".
One weekend, noticing the 4341 spinning a pair of GCR drives at over
half their rated 275 ips, I was shocked to learn that it was reading
the disk file-by-file, not track at a time.  BSD filesystems just
can't compare to what this 2-MIPS machine could do with apparent ease.

How do they get that kind of throughput?  I refuse to believe that it's
all hardware.  Mainframe disks rotate at 3600 RPM like everybody else's
and their 3 MB/s transfer rate is only slightly higher than a SuperEagle.
A 2-MIPS CPU would be inadequate to run a BSD filesystem at those speeds,
so obviously their software overhead is a lot lower, while at the same
time wasting no disk time.  What is VM doing efficiently that Unix does
inefficiently?

Don Speck   speck at vlsi.caltech.edu  {amdahl,ames!elroy}!cit-vax!speck