I'm using Photoshop CS6 on a desktop running Windows 7 with AMD Radeon HD 6750 and I noticed that when I zoom at 66.7% or 33%, the pictures edges look "jagged"/blurry, etc. and the image only has a smooth rendering at 100%, 50%, 25%, etc.
I wouldn't ask about this except, I have the same exact version of Photoshop on my laptop, running Windows 7 with Intel's HD 4000 built-in graphics, and this computer displays smooth rendering of images at any zoom level, no matter what. So why the difference? The settings in the Preferences > Performance section is identical on both computers.
Look in your Edit - Preferences - Performance dialog. Is [ ] Use Graphics Processor selected? I'm guessing not.
If it's off and you can enable it, try doing so.
In any case, go to the AMD web site and get the latest display driver (Catalyst) for your hardware and OS.
Yeah, sorry. Computer won't let me update the driver. First I installed the wrong one and crashed the computer, then I reinstalled the old one, downloaded the correct one, it installed, no crash, the computer restarted and it told me I had no driver, so I had to reinstall the old one. No hope of updating apparently. I hope that wasn't the solution to the Photoshop problem >.<
I also keep getting conflicting messages from my computer. Photoshop said I had the 6750, but Windows said I had the 5750. When the second install failed (of the 5750), Windows now tells me I have the 6750. I don't get it. But I guess this a question I should ask AMD.
Perhaps a complete removal of AMD/ATI drivers and a bit of diligence to make sure they're completely removed would be in order. See the instructions from AMD that I posted in reply #7 in this other thread for details: