Subject: Re: what's this machine check mean?
To: Ross Harvey <>
From: Wilko Bulte <>
List: port-alpha
Date: 04/17/2000 23:25:12
On Mon, Apr 17, 2000 at 01:43:20PM -0700, Ross Harvey wrote:

> > > Yes - but each *data* line is still connected to only one chip.
> >
> > But via substantially longer PCB traces. Anyway, these adapters are
> > not a very good idea on any system.
> For the RAM trivia collectors, a couple of subtle problems with RAM
> socket gizmos is:
> 	The older ram cards they adapt are often two-layer, whereas
> 	the vanilla 70 nS FPM modules invariably have ground and power
> 	planes. So, high - Z traces with Z discontinuities and multiple
> 	long forks. (Www, forks in transmission lines attract evil.)

Yep, high freq PCB layout is an artform in it's own right.

> > Well, I wonder why they would not use standard data buffer chips instead
> > of logic gates (F04, F08)?
> Because standard data buffer chips are bigger physically, slower, a lot

Somewhat bigger, true..

> more expensive, and use more power. The chips are there to isolate, not
> to produce a lot more DC drive than a 72-contact SIMM DRAM would have had
> anyway. And extra drive makes the transmission line problems worse, not
> better.

It highly depends on what kind of driver chip you are using. F-TTL is
probably better for lousy layouts than fast Cmos designs. Anyway, we are
diverging from the subject ;-)

> Sadly, should your axppci33 actually work "perfectly", it's lack of speed
> will be so pronounced that the distinction between "perfect" and "broken"
> will be meaningless.  Sorry to be discouraging, but you need to know this
> before you spend too much time beating your head against it...

Ah, well, speed. No. ;-) But they are usable, esp. for people who just want
an Alpha to play with. NoName boards were sold in the Netherlands last
November new-in-the-box for US$ 12 each. At such a price one cannot complain
about price-performance ratios.

> Having said that, cjs somehow managed to build a set of snapshots and
> a release or two on one. Don't ask me how.

With extreme amounts of patience this can be accomplished.

> Those come with and without cache, BTW. I'm not sure what the speed
> contribution of the cache is, although it feels funny to even use
> the word "speed" when referring to an LCA box. :-)

Without cache life becomes rather miserable.

Wilko Bulte 		Powered by FreeBSD