Hooked On Composite, Need New GPU

[Lennart Sorensen]

On Wed, Dec 20, 2006 at 01:24:41PM -0500, JoeHill wrote:
> Well, I must say, your first note scared the bejeezus out of me, because, like
> the impulsive person I am, I already ordered the 7600!
> 
> ...but, my heart rate has gone down now, thanks :-)

Actually some 6800XTs don't have the high memory bandwidth.  They make
both 128bit 1000MHz and 256bit 700MHz apparently.  It looks like the
specs for that particular card makes it one of the faster ones.  Still
memory bandwidth isn't useful if you don't have processing power to
generate pixels.  The 7 series also do anti aliasing much faster, as
well as shader model 3 (not sure that applies to opengl drivers or not).
I think the 6 series was limited to SM2.

> One thing: (well, two): how important is the 'dual core' bit? Does that enable,
> like the name seems to imply, parallel processing of some kind?

Well dual core means you have two processors.  So a Core 2 Duo 6400 is a
pair of 2.13GHz processors in one chip.  So you can have two programs
each running on one core at full speed (well they have to share memory
bandwidth of course).  A single program that doesn't use threads won't
get any benefit from having 2 cores though, other than the small gain
the kernel running on the other core might bring or perhaps the X server
running on the other core.  I don't think I would ever buy a machine
that wasn't at least dual core anymore.

> ...and:
> 
> The RAMDAC in general, which is somewhat faster (and 'dual core', if that
> matters). I did some Googling before I ordered, and I got the impression that
> the speed and, for lack of better term, size, was a big boost. No?

The RAMDAC (RAM Digital to Analog Converter) is what converts the data
in videoram into the analog signal going to the display (in the case of
an analog display that is).  Almost everything today has 350 to 400MHz
RAMDACs which handle 2048x1536 at 85HZ which ought to be plenty.  LCD
displays using DVI-D connections use the TDMS transmitter rather than
the RAMDAC so it doesn't actually matter that much anymore.  Some new
cards have duallink TDMS transmitters (which can run up to 2560x1600 LCD
screens at 60Hz) while most cards, especially older ones are limited to
single link which allows up to 1920x1200 at 60Hz (if they skip the blanking
interval) or 1600x1200 at 60Hz (using standard timing).  Given CRTs seem to
be going away, the single link DVI vs. dual link DVI is probably much
more important than the ramdac speed.

> Thanks for the info!...but jeez, at first I thought 'Oh crap, I fell for the
> 'BFG' thing like a total sucker'.
> 
> Well, I kinda did, but...

It's a tradeoff.  Making a card with a 256bit memory bus is expensive.
So many traces on the board.  The 7600GS chip is much faster than the
6800XT chip, but the 6800XT has a 256bit memory interface making for a
more expensive board design, even though the chip itself is probably
cheaper.

By the way, the 6800XT does not have any dual link DVI.  The 7600
usually has one dual link and one single link, or sometimes one dual
link and one analog VGA.

--
Len Sorensen
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