It's possible that it depends completely on the chip, and the implementation of said chip - I know that the Mobility Radeon 9000 doesn't have it.
just to make your suspicions about it not dependign on the chip, I came across a sony vaio once with a radeon 9000 IGP at comp usa. It had the option. 95% of vaios have the option. What do vaios have that others dont? a screen driver!!
My conclusions on fixed scaling on ATI:
just to let you know where I am this far,
and regarding this:ok guys, i made a new discovery. This problem seems to ONLY arise on 1280x800 screens. And I figured out why. It may be just coincidence but for 1440x900 screen, a 4:3 resolution that was stretched and had a preserved ratio would be stretched to 1200x900. For 1680x1050, it would be stretched to 1400x1050. For 1920x1200, it would be stretched to 1600x1200. And finally, for 1280x800, it would be stretched to 1066.66667x800
therefore I conclude:
1=> fixed scaling is made available or not relative to revisions or batches of chipsets (sheer luck is needed)
2=> fixed scaling is made available or not through a video BIOS setting (flashing is needed, and maybe hacking the bios)
3=> fixed scaling is made available or not relative to the panel connected
4=> fixed scaling is made available or not relative to a complex combination of parameters
I posted that resolution thing and since then I have found many more findings simlar to yours, which makes me take back what I said. And as far as opinions go for your possibilities. I really think its number 3 and only number 3. Something makes me doubt the other possibilities. I have more proof to back this up too. I posted this on driverheaven. Theres a lot of people complaining about this there as well.
This subject is so old... people have been complaining about this since like catalyst 3.5 or somethin. You would think it would be resolved by now. I sent a ticket to ati for this myself. Their response was lame. This PISSES ME OFF!!!!!!! I have a laptop computer with a 15.4 inch display and a radeon 9000 IGP. I, too, am missing this aspect ratio option. He gave me this bs about ati support being the manufacturers problem. He also told me if it was a desktop problem, then it must be a fault of screen drivers, which is extremely lame... especially if nvidia doesnt need screen drivers. So I finally managed to make him pinpoint the problem. I have no idea if he is bsing (tech support people dont always konw what they're talkin about), but he seems believable. I asked him about the issue where a screen has no drivers. Here is what he said:
"Then you would have a problem with the monitor. If it does not have drivers and relies on EDID information there will be issues. It is a similar problem that the laptops have. There is no information provided by the screen to the drivers, the dirvers have to be custom written for the display."
So if any of you good programmers/hackers/reverse engineers can figure out how to write a screen driver or spoof the EDID or somethin, then maybe we can get somewhere. But still. THIS IS SO LAME!!!!!! SCREW YOU ATI!!!!!!!!
At the moment, my laptop is being repaired so I cant try cat 6.6. Has anyone tried it yet? Not that there is much hope they fixed it...
heres the link if you wanna read it http://www.driverheaven.net/showthread.php?t=105057