🚀 go-pugleaf

	I'll preface by commenting that we have both an 11/780 (Ultrix 3.1, 3 x RA81,
	2 x Unibus, TU77's, etc. etc.) and have had a DS3100 (Ultrix 3.0, 322MB drive, TK50 - ugh! ) 
	for a year.
 
> It is *not* *fifteen* times faster than a vax 780! the DS3100 is a RISC

	True.  On some of my applications it is 30 times faster :-)

	MIPS ratings are usually based upon timing tests performed on 1 or 2
	specific test suites such as the infamous Dhrystone & Whetstone tests.
	For the DS3100, the test they selected obviously runs 14 times faster
	than on an 11/780, ergo the sales rep spouts ITS A 14 MIP MACHINE.

	My perception of reality is that it averages to about a 9 MIP machine,
	a tad faster than the SparcStation 1 (but what about the SS1+? :-),
	as normalized to our 11/780.

> execute fifteen times as many of its instructions in one second as a VAX780
> can of vax instructions, you're comparing apples and oranges. Each Vax
> instruction accomplishes perhaps the equivalent of eight DS3100 instructions.
	
	However, a RISC box would execute its 8 instructions a lot
	faster than the 780 would execute its 1 instruction.
 
> I'm not saying that the DS3100 isn't faster than a vax780 anyway, I'm just
> saying that you can't blindly quote MIPS ratings and expect it to truly
> reflect the relative performance of two totally different architectures. 

	Yup.  SPEC or DR ratings are even better (although still not great), 
	but the best thing anyone could do is to try before you buy, if 
	at all possible, with your own applications.
 
> Also, Instructions per Second is not a complete description of the power
> of any computer - there are many other considerations; for example, Bus
> I/O speed, transfer rate, caching, etc. I'm not sure what kind of bus the
> DS3100 has (is it Qbus? I haven't gotten mine yet) but the Vax780 has a very
> fast bus indeed, and as far as handling many terminals, a fast bus is far

	SCSI.  The Decsystem 5400 uses the Q-bus as the I/O bus.  

	The throughput ratings of the 2 buses are similar.
	
	SCSI - 4 MB/sec asynchronous, 5 MB/sec synchronous (theoretical)
	Q-bus  5 MB/sec (theoretical), ~3.3 MB/sec actual maximum throughput
	Unibus - ~2 MB/sec (theoretical), ~1.2 MB/sec actual maximum throughput

	The 11/780 uses the Unibus for the Ethernet interface and for the RA series
	drive controllers.  

	I'll defer on the Massbus, since only the older hard drives (RK, RM series)
	use it directly, and their performance leaves much to be desired, even
	against the RA81.

> more important than a fast processor - my PDP-11/34 can handle 8 users
> better than a fast DOS machine with an 8 terminal board, though the AT 

	If I were single streaming batch jobs, I'd take the AT any day.

	You are absolutely, positively, correct if you are talking about
	an interactive environment.  We get better interactive thoughput
	from our 11/84 (.72 MIPS) running RSX than we do from our 11/780.

	However, at least part of this discrepancy is probably due to
	the relative sizes and efficiency of the RSX executive vs. the
	Ultrix kernel.

	The odds are pretty good that a fast processor will keep a slow bus
	working at close to its maximum bandwidth.

	To conclude:

	In my experience the 780 is a slug compared to the DS3100, and is
	much more expensive to keep around.

	I remember an article published in the DECUS newsletter last year
	about someone porting their application to a DS3100 in order to
	do a performance evaluation; as I recall, they ported some of their
	simulations written in Fortran.

	In comparing the DS3100 to their VAX 8810:

		The DS3100 smoked the 8810 big time for compute-intensive
		applications.

		The 8810 offered 2x the speed of the DS3100 for I/O intensive
		applications.

	However, they were comparing a $500,000+ machine vs. a $30,000
	one.
	
 
-- 
Larry Beaulieu 			When up to your a** in alligators, it's
SMTS/Software Engineer		difficult to remember that your original 
GCA Corporation, 		objective was to drain the swamp...
Andover, MA	...uunet!gca!beaulieu	The usual disclaimers apply.