[Info-vax] Y3K for PDP-11 Operating Systems

[Johnny Billquist]

On 2011-05-09 15.47, vandys at vsta.org wrote:
> In alt.sys.pdp11 Rob Brown<mylastname at gmcl.com>  wrote:
>> It seemed to me that the 11/750 was even slower than an 11/44, but
>> perhaps that had something to do with their respective workloads.
>
> For anything not requiring 32 bits, I'm quite sure the 11/70 outran it, in
> both integer math and string handling scenarios.  Floating point, I'm not
> sure--not an area where I had to deal with performance.

I wouldn't be so sure on string handling, since the VAX have lots of 
native instructions to deal with that, which the 11/70 do not. Integer 
on the other hand, yes.
Floating point as well, unless you want some VAX-specific format.

The 11/44 is a bit slower than the 11/70, but still pretty ok. And for a 
lot of things, the PDP-11 have much lower overhead than a VAX, such as 
subroutine calling and interrupts. I'm not sure if context switching is 
better or worse. The VAX have a single instruction for that, while the 
PDP-11 needs to manually handle both processor registers and MMU 
registers. On the other hand, you don't have the penalty of the TLB 
cache flushes, and I don't know how fast/slow the context save/restore 
on the VAX are.

	Johnny