Is ULTRIX-11 really slow?

[Dan Ts'o]

> A friend recently brought up ultrix-11 on a microPDP11 with
> an 11/73 processor.  He claims that with 2 users running the
> system is really slow.  DEC support told him that ultrix-11
> has NO BUFFERING on terminal I/O (that is, characters are
> all output as they are sent to the driver).  And that there
> is no buffering in the usual stdio routines.

	Yes most older versions of UNIX did not buffer tty output from the
stdio package, although the kernel stashes write requests in an output
queue. Tty stdio buffering just reduces system call overhead and in some
cases, hardware setup overhead. I believe that ULTRIX-11 is based on V7M,
which might be a little slower than VENIX-11, PWB/Unix or 2.9BSD.
	But my best guess at the reason that your friend's 11/73 system is
so slow is the Micro11's disk, the RD51/2 with the RDQX controller. This
disk subsystem has got to be the worst performer in DEC's history (although
it is the cheapest DEC disk ever). I would serious consider an RX02 floppy
to be a performance rival. The RDQX controller has a T-11 chip (of Falcon
11/21 fame (a real performance dog)) and it literally takes seconds to
respond.
	Otherwise the 11/73 is quite a speedy CPU. It is just under an 11/44
and should be able to support say ten average users if it had enough memory
and a good disk. I put an Eagle on our 11/73 and it hums right along (running
a version of PWB/Unix.) Another site I know of uses an 11/73 with a CDC 9448
and VENIX-11, and it is also quite a speedy system -- runs with six users all
the time (its all there is) with no response time problems.
	In a series of UNIX system benchmarks, our 11/73 with the Eagle varied
between .14 and .67 of an 11/780 (w/ FPA, Eagles and 4.2BSD), averaging .37
The largest differences (.14, .16) were due to floating point and file copying
(thanks to 4.2BSD's fast filesystem) and the smallest different .67 was running
the integer sieve benchmark. The 11/73 nroff benchmark ran at .34 of the 11/780.
So crudely speaking, if your 11/780 can support 30 users, the 11/73 should be
able to support at least ten users.

					Cheers,
					Dan Ts'o
					Dept. Neurobiology
					Rockefeller Univ.
					1230 York Ave.
					NY, NY 10021
					212-570-7671
					...cmcl2!rna!dan