Benchmark Wars (was Re: gauging interest in VAX 6000-530)

From: Chuck McManis <cmcmanis_at_mcmanis.com>
Date: Sun Oct 24 18:43:01 1999

At 04:01 PM 10/24/99 -0700, Mike wrote:
>(Hi Chuck!)
>
>Here's my back-of-the-envelope:

[snip]

Ok, you've considered the memory bandwidth without considering:
         1) That disk transfers also happen across this bus.
         2) Other I/O (mouse? Sound? Video?)
         3) The interrupt load on the CPU.

As an empirical note the 16450 UART often could not be serviced fast enough
by the 486DX66 to prevent it from dropping incoming characters above 9600
baud. That was even with the "FastCOM" driver that came with Procomm plus
for DOS, not until the 16550 added a 16 (or was it 32) character FIFO did
it work. Now multiply that by 12? Say 9600 baud, every types a key. That is
12 interrupts to service while you're potentially trying to push out 12
streams of bytes.

Anyway, the VAX (and most DEC gear) got around this by having channel
processors _everywhere_ and of course the modern PC has channel processors
_nowhere_. (IDE taking this to the logical extreme)

Somewhere I've got an 8 port serial card that was built for the 16 bit ISA
bus (it has 8 mini-din connectors on the card edge). The thought was to run
UNIX on a 486 and use terminals for multiple students. It didn't work. The
PC couldn't keep up. I fully admit though that given source code I might
have been able to make it work :-)

--Chuck
Received on Sun Oct 24 1999 - 18:43:01 BST