RAM – can Photoshop CS3 cope?

April 20, 2007

Prodig subscribers have recently been asking ‘Is PS CS3 able to cope with more RAM?’.

Adam Jerugim and Russell Williams, from Adobe, have contributed these answers…

Photoshop can and does take advantage of more than 2GB of RAM. What you’ll need is an OS that supports that much RAM (XP 64-bit, Vista 64-bit, or OS X) and > 4GB of physical RAM. If you have more than 4GB of RAM we enable VM OS buffering to take advantage of nearly all the RAM in your system (we’ve tested up to 16GB FWIW). Note that this feature is on by default in CS2 for Mac and off by default in CS3 for Mac, so in order to enable it for CS3, you’ll need to use the ForceVMBuffering.plugin that is included in the optional plug-ins folder.

Other suggestions to increase your large file performance include enabling the bigger tiles plug-in, using a dedicated RAID0 setup for PS scratch, and using a very fast (I suggest WD Raptor 10K SATA drives) as your primary OS volume (the one that PS is installed on).

- Adam

We’ve tested with 6-8 GB of RAM and seen significant improvements over systems with just 4GB. Photoshop can’t directly address the extra RAM beyond 4GB, but we cooperate with the operating system to use it.

Most of the RAM assigned to Photoshop is used as a cache of the contents of the scratch file — we’re trying to keep as much image data in RAM as possible. When there’s more than 4GB in the machine with a 64 bit OS, we can tell the OS to use the rest of that RAM to keep image data that Photoshop can’t directly address. We do this by “turning on VM buffering” (telling the OS to provide buffering for our scratch file).

It works well on Windows, but on Mac there’s a problem. As Adam mentioned, it’s on by default in CS2 and CS3 for Windows, on by default for CS2 Mac, and off by default for CS3 Mac. You can download a plugin from adobe.com to explicitly enable or disable it.

The problem on Mac is that with VM buffering on, MacOS pauses Photoshop about every 30 seconds for short and varying amount of time; this causes big problems if you’re painting a lot. If you’re mostly doing whole image operations on big images, it’s still a huge win to have 6-8GB and VM buffering on.

So on Windows, you’re all set. Vista in particular seems to do great with lots of RAM (better than XP). Just load up your box with lots ‘o RAM and either CS2 or CS3 will work great.

On Mac, you have to decide whether you can live with the pauses. If so, load up with RAM and if you’re running CS3, use the plugin to turn on VM buffering. If the pauses are a problem for you, use the plugin to turn *off* VM buffering if you’re running CS2. Photoshop will ignore RAM beyond 4GB. If this matters to you, I suggest sending a note to Apple asking them to fix the OS problem.

- Russell

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