Several Photoshop features require a video card that has at least 512MB of vram.
Here are the cards they have tested for compatibility. But the below list does not mean all cards will run all features.
nVidia GeForce 8000, 9000, 100, 200, 300, 400, 500, 600 series
nVidia Quadro 400, 600, 2000, 4000 (Mac & Win), CX, 5000, 6000, K600, K2000, K4000, K5000 (Windows & Mac OS)
AMD/ATI Radeon 2000, 3000, 4000, 5000, 6000, 7000 series
AMD/ATI FirePro 3800, 4800, 5800, 7800, 8800, 9800, 3900, 4900, 5900, 7900
AMD/ATI FireGL W5000, W7000, W8000
Intel Intel HD Graphics, Intel HD Graphics P3000, Intel HD Graphics P4000, Intel(R) HD Graphics P4600/P4700
If you are working with very large canvases, I would get a real GPU. Does not have to be high end. An HD7750 would do great for most things. But if you just use this on the side for your own stuff, may not be worth it.
Further details are here:
http://helpx.adobe.com/photoshop/kb...ics hardware not officially supported message