[KLUG Members] Re: XFree86 and AGP4 -- AGP "speeds" != AGP GART

[Bryan J. Smith]

--=-8GDsWRCBse09vnlUmL53
Content-Type: text/plain
Content-Transfer-Encoding: quoted-printable

On Wed, 2003-01-08 at 09:52, Bruce Smith wrote:
> Interesting, but now for something more practical from the non-hardware
> guy in the crowd:
> We bought a new PC at work, and I wanted to move the best video card to
> the desktop PC, and the cheaper video card to the server.  Anyway ...=20
> while swapping the AGP video cards, I found that there are slight
> differences on the new AGP cards from the old AGP cards.  The card edge
> (that plugs into the mobo) is slightly different, but different enough
> that the two cards were NOT interchangeable!  They could not physically
> be plugged into the other PC's!
> I don't the correct terminology of these two different AGP card slots.
> (but I'm sure Byron will tell us, if we ask :)

That's a "form-factor key".

They are commonly used to prevent you from putting in a board of a
different voltage into a slot of a different voltage.  E.g., PCI +3.3V
and +5V slots.  Some PCI cards and slots can do both, some can't.

In the case of AGP, they keyed the speed too.  It prevents you from
inserting a video card that only supports certain AGP speeds into
another.  E.g., there is a key for AGPx1 (66MHz signaling), another for
AGPx2 (133MHz signaling) and AGPx4 (266MHz signaling) has another key (I
believe? or no key?).  Haven't messed with AGPx8 yet, but I bet it has
another key (or not?).

Most ViA and AMD mainboards with AGPx4 I've seen have an "universal
slot" which supports all AGPx1, x2 and x4 because the slot itself is
keyless.  Although it can become an issue with newer AGPx8, which
expects another key (or not?).

And if that isn't confusing enough, have you heard of AGP-Pro?  It's not
faster nor 64-bit performance, it's for providing additional power --
via an extension (some "regular" AGP cards have a leading "PCB" sticking
out in front of their "regular" AGP connector).  AGPPro-50 provides upto
an extra 25-50W, and AGPPro-100 provides upto an extra 50-100W.

> Did someone change the AGP standard and forget to inform me?!?!?  :-)
> Just like VIA started making CPU's, and nobody told me!

No, it's just a key.

And as far as ViA, long story, but they are former IDT Centaur WinChip
and Cyrix M2 designs.  Which explains the "C3" product name (Centuar M3
;-).

> Is there a mailing list or web site out there for non-hardware guys like
> me who just want to know the practical differences like this, and new
> hardware advances? (like the VIA CPU's)  I do NOT want to know the
> internal chipset / cardedge pinouts / instruction set changes / and
> other stuff that makes my eyes glaze over.

Engineering design sheets man!  I often know _before_ the enthusiasts
sites visit a hardware conference.

> I also don't care every time a chipset maker comes out with a slightly
> faster version, or a "new" chipset that's just based on the old one.=20
> I only want a nice overview of MAJOR changes.  This is for someone who
> is dangerous enough to turn a screwdriver, install new hardware, and
> hope it works. (but doesn't give a rip HOW it works :)

Well, that there is the "problem."  If you want to stay "bleeding edge,"
you need to read the "boring" engineering stuff.  It doesn't take a
computer engineering degree to do so (although you'll absorb a lot more
of "why").

E.g., Why does a 256MB DIMM module only show up as 128MB?

Because when it comes to computers, it's more than just "throughput and
latency."  There are even just simplistic analog and digital aspects to
worry about too.  It's nice if you learn these, but you don't have to.

But there are _endless_ variables.

Which is why things like "keys" exist.  To prevent you from putting in a
particular voltage/speed card in the wrong slot.  Because you, the
technician, might not know why they exist.


--=20
Bryan J. Smith, E.I. (BSECE)       Contact Info:  http://thebs.org
[ http://thebs.org/files/resume/BryanJonSmith_certifications.pdf ]
------------------------------------------------------------------
* A lecture on software piracy from Bill Gates is like a lecture *
* on adultry from the owner of a brothel of other people's wives *


--=-8GDsWRCBse09vnlUmL53
Content-Type: application/pgp-signature; name=signature.asc
Content-Description: This is a digitally signed message part

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.7 (GNU/Linux)

iD8DBQA+HEWmDjEszaVrzmQRAn5KAKCjd7Ig84PhqICNzk8RuRho6d837ACgzlS4
rrutwfY6k///Uwzo1Natn4s=
=u2TX
-----END PGP SIGNATURE-----

--=-8GDsWRCBse09vnlUmL53--