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Posted By: JoBoy Snow Leopard graphics card - 08/25/09 03:27 AM
I have a standard ATI Radeon HD 2600 XT graphics card on my Mac Pro. It is not listed as one of the cards that should be used with Snow Leopard. What will be the consequences if I don't upgrade to one of the preferred cards?
Posted By: dkmarsh Re: Snow Leopard graphics card - 08/25/09 11:28 AM

The graphics cards you're referring to are those which are compatible with Snow Leopard's OpenCL technology, which allows unused graphics processing power to be tapped by other applications. Basically, it's a way of boosting processing power beyond that available through the CPUs.

The usefulness of OpenCL depends on what kind of apps you're running, and whether their developers have programmed them to take advantage of it, but in any case, I don't think there's a reason to consider upgrading unless/until you find yourself working in an OpenCL-savvy application and wishing it were faster.
Posted By: JoBoy Re: Snow Leopard graphics card - 08/25/09 04:47 PM
I was concerned because Photoshop CS4(v 11.0.1) limits me to opening 4 images when I check Enable Open GL Drawing in preferences. By unchecking it, I can open a large number of images at the same time. I don't yet know much about Open CL. It was the GL that prompted me to ask about the card.
Posted By: macnerd10 Re: Snow Leopard graphics card - 08/25/09 05:20 PM
According to the link below from Apple
http://www.apple.com/macosx/specs.html
the JoBoy's graphic card may not be compatible with OpenCL. At least it is not listed among those that are. As per posts on other forums, the other features like Grand Central may be OK.
Posted By: donikatz Re: Snow Leopard graphics card - 08/25/09 05:42 PM
Yes, that was DK's point, that the only 10.6 GPU incompatibility is with with OpenCL, which prob isn't a big deal.

To respond to the OP's last point: It's likely that unless Adobe builds OpenCL support into Photoshop, it won't help you to upgrade your card. We'll certainly have to wait and see what happens with industry support for OpenCL. Apple is often an early adopter on certain standards, so that often means we have to wait a bit to see if we can take any real advantage. For the time being, not reason to upgrade your video card just for OpenCL.
Posted By: JoBoy Re: Snow Leopard graphics card - 08/25/09 06:44 PM
Thank you. Very helpful.

Would an upgraded card eliminate the 4 image limit on Photoshop when Open GL is activated? Would more RAM help? I have 2Gb at present.
Posted By: donikatz Re: Snow Leopard graphics card - 08/25/09 07:05 PM
That's a good question. I believe in this case you're being limited by VRAM, not by system RAM. I think a card with 512 MB VRAM would allow you to support more images at once. I've read that PS with OpenGL is a VRAM hog and doesn't give back the memory gracefully, so that you're best off quitting PS in between uses to free up the VRAM for next time.

Also note that OpenCL is very different from OpenGL. Whereas OpenGL allows you to utilize your GPU/VRAM for better screen redraw and display rendering (video-related things), OpenCL conversely allows you to take advantage of unused GPU cycles and use them to offload regular processing (non-video things). Or at least that's how it's explained. So I'm not sure it will make sense for Adobe to use OpenCL with PS, since PS is the sort of app to want to use the GPU cycles for video, not hand them over to other processing. It's possible OpenCL will in fact specifically be disabled during PS use for just this reason. Or it's possible PS with OpenGL + OpenCL will allow even better results, with OpenGL leveraging the computing of OpenCL to calculate AND display quicker/better. Again, this is all speculation at this point. I don't know how it will be controlled (will there be a toggle switch in the OS or in the specific apps, will it be on demand or can it be manually regulated?) or implemented across the industry -- we'll have to wait and see.
Posted By: JoBoy Re: Snow Leopard graphics card - 08/25/09 11:09 PM
OK, I can see that. Does Photoshop's scratch disk provide virtual memory to augment system RAM instead of augmenting graphics RAM?
Posted By: JoBoy Re: Snow Leopard graphics card - 08/26/09 01:24 AM
I got a little info from the Photoshop writeup on Adobe's web site. From what I was able to glean, a scratch disk is virtual memory for Photoshop while virtual memory for the system is on the boot volume. That's why I have to locate the scratch disk on a different internal volume so that Photoshop and the system don't compete for the same disk's virtual memory resources. I've been doing this blindly for a long time, but haven't taken the time to find out why.

Open CL is not related to RAM or virtual memory. Open CL allows the system to use some of the GPU's processing power to supplement the CPU. Photoshop's limitation on image processing with my 256Mb GPU is to steal a little processing power to help the CPU.

Grand Central Dispatch will enable more efficient use of the multiple cores in the CPU. In concert with Open CL, it is expected to increase the throughput of my Mac without my buying any more hardware, but if I want to really join the power users' club, I'll get a new graphics card with more VRAM.

Did I get it right this time?
Posted By: donikatz Re: Snow Leopard graphics card - 08/26/09 04:09 AM
Did I get it right this time?

Almost. While it's true that OpenCL is related to processing and not memory, the simultaneous window open limitation we discussed related to your 256 MB VRAM in your graphics card is related to OpenGL, not OpenCL. The problem is not that your Mac doesn't have enough processing power to handle many images at once, it's that OpenGL doesn't have enough VRAM to handle the enhanced display of many images at once. You can either get more VRAM (a new card) or turn off OpenGL.

As for Grand Central, yes, it will allow more-efficient multicore operation, which in concert with OpenCL can allow it to spread processing across multiple cores AND multiple processing units (CPU, GPU). Again, how this would be utilized in a Photoshop workflow remains to be seen. It's possible Adobe won't take advantage of this until CS5 or later or not at all. I expect once 10.6 drops on Fri, we'll start seeing more in-depth reports and benchmarks. Again, though, this part is related to processing (CPU/GPU) not necessarily image display (OpenGL). But of course OpenCL can potentially work behind OpenGL to calculate faster what OpenGL will help display, thereby enhancing the entire experience. But it's all too early to see how this will all come together in the real world.
Posted By: JoBoy Re: Snow Leopard graphics card - 08/26/09 04:45 AM
Thanks. I really appreciate it.
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