UNIX performance on a VAX & 68020

[Joel Clark]

In article <54190 at sun.uucp> guy at gorodish.Sun.COM (Guy Harris) writes:
>> Benchmarks show that a 68020 is at least as fast as a VAX-11.
>> But if I start e.g. 6 C-compilers on a UNIX-system running on a 68020,
>> the performance collapses completely (even when no swapping is necessary),
>> where on a VAX the system-performance stays reasonable.
>> I wonder why this is so, when the CPU-speeds are roughly the same.
>
>I don't see that you can make a generic statement about "UNIX systems running
>on a 68020" here.  (For that matter, you can't make generic statements about "a
>VAX-11; I presume you have some particular VAX, such as a 780, in mind.)  68020
>UNIX machines may share the same CPU, but may run at different clock speeds, or
>have different memory management units, or....
>
I once had the pleasure of porting a compiler to about 20 different vendors
Unix 68020 boxes.  The porting changes were limited to different
spellings for many of the system DEFINEs and different signal handling.  The
resultant compile time speed varied from 7 lines a minute to 3500 lines a 
minute.  When the machine that produced 7 lines a minute had brk() and sbrk()
rewritten it produced 100 lines a minute.  So there is a great variance between
680X0 boxes.  However when any of these boxes were compared to a Vax 11/750 or
Vax 11/780, as the number of compiles executing increased the relative speed
degradation (per box) was always greater on the 680X0's.  I believe the Vax
is much better design for 30 to 200 users then any 680X0 box I've seen.  

Joel Clark
Intel Scientific Computers               joel at intelisc.uucp
Beaverton OR. 97201			 {tektronix}!ogcvax!intelisc!joel
(503) 629-7732