View Full Version : Allocating >3GB to CS3

12-07-2007, 10:43 AM
Hello everyone,

I have a MacPro 2.66 Dual core Xeon with 8 GB of RAM and would like to increase the allocated RAM to CS3 above the 3GB....anyone know how to do this?

I read this on the Adobe site..."When you run Photoshop CS3 on a 64-bit operating system, such as Mac OS X v10.4 and later, Photoshop can access up to 8 GB of RAM..."

Now when I go to preferences and then performance in CS3...the max allowed is 3 GB. I have been told that that will be the max shown, but in fact it will use more...is this true, or am I missing something? Do I have to change something to allocate say 6gb's?

thanks for any help you can offer.


12-07-2007, 04:18 PM
Hi Gabe, welcome to the forums-

If you activate the ForceVMBuffering plugin, you'll allow the operating system to cache more of Photoshop's scratch disk data in RAM. This will speed up operations and take better advantage of your 8GB installed RAM.

Also- consider activating the Bigger Tiles plugin; you'll enjoy generally faster performance.

The memory slider in Photoshop's "Performance" preference pane should generally be kept at around 70%, rather than boosting it to 100% which is tempting. This is because the operating system will run better when doing what Photoshop tells it to do when it's given this "extra" amount of available RAM that Photoshop could in theory use just for itself.

Here is my (potentially imperfect) understanding of how RAM is allocated with Photoshop CS2 on up:

With your 8GB of RAM, a 100% memory setting in CS3 is 3072MB.

The addressable memory footprint for Photoshop as a 32bit application is 4GB, but Photoshop code is written to subtract approximately 3-400MB from 4GB and reserve this as a minimum for the operating system to use in order to function. The other approximately 600MB+ above 3072MB can be used by Photoshop either for plugin calls which need large chunks of contiguous RAM and/or for initial cache of scratch disk data. The 3072MB is reserved for image data only. The ForceVMBuffering plugin is required to use installed RAM above 4GB to cache scratch disk data.

When you leave the memory setting at 70% or approximately 2150MB "used by Photoshop", the operating system has a nice healthy roughly 1.2GB (of 4GB) of available RAM to do Photoshop's bidding, and not be "starved"- and also allow up to 4+GB of scratch disk data caching when 8GB RAM is installed.

The Adobe info "When you run Photoshop CS3 on a 64-bit operating system, such as Mac OS X v10.4 and later, Photoshop can access up to 8 GB of RAM..." is actually somewhat erroneous. In reality, Photoshop can "use" more than 8GB of installed RAM: if allowed, Photoshop will cache scratch disk data in all available RAM beyond 4GB in machines with more than 8GB installed. I've seen this for myself on a machine with 16GB installed RAM and have been told the same is true in machines with 32GB installed RAM.

Hope this helps. You could also check out our guide: Photoshop Acceleration Basics (http://homepage.mac.com/boots911/.Public/PhotoshopAccelerationBasics2.4W.pdf)

12-07-2007, 05:32 PM
Finally someone who actually knows what they're talking about. Thank you for that reply...that is more info then I have gotten anywhere else...even Adobe Technical phone line. So again thanks for that...very much appreciated.


12-08-2007, 06:38 AM
Your welcome, Gabe.

8GB installed is the amount generally considered as the "sweet spot" for G5s and MPs for serious Photoshopping of image files large and small; ie, the best cost/benefit ratio. While more certainly can help (depending on the workflow)- startup disk and scratch disk hard drive choice and configuration needs to be addressed at some point for overall maximum acceleration.