4 Replies Latest reply: Nov 17, 2011 10:55 AM by Chris Cox RSS

    Photoshop CS4 not using RAM

    John Smith for example Community Member

      I'm aware that Photoshop CS4 (Mac) is a 32 bit application and therefore limited to 4 GB of RAM.

       

      My Mac (OSX Lion) has 8 GB of RAM. So I would expect Photoshop to use 4 GB of it, but in the preferences dialogue it only lists 3072 MB "available" RAM, and even suggests to only use 1689 – 2211 MB of it. (Obviously Photoshop assumes that the Mac has not more than 4 GB of total RAM and that the user must be protected from allocating too much RAM to Photoshop.) But although I told Photoshop to use at least those 3072 MB which it assumes to be available, it doesn't even do that: According to the activity monitor, no matter how big a file is and how low the "efficiency" drops, it never uses more than 2.45 GB of RAM.

       

      What's going on? How can I make Photoshop to use at least those 3072 MB? Is there a trick to make it use the full 4 GB which it should be able to see?

        • 1. Re: Photoshop CS4 not using RAM
          c.pfaffenbichler Community Member

          It seems 3GB is the maximum, see »Max out on RAM«

          http://kb2.adobe.com/cps/404/kb404439.html

          • 2. Re: Photoshop CS4 not using RAM
            John Smith for example Community Member

            Yes. Hence my two questions:

             

            – How can I convince Photoshop to use at least those 3072 MB which it claims to be able to, instead of those 2.45 GB it actually only does no matter what I'm doing?

             

            – Is there some unsupported dirty trick to make Photoshop use the whole 4 GB which it theoretically should be able to, of course entirely at my own risk?

            • 3. Re: Photoshop CS4 not using RAM
              Jeff Schewe Community Member

              John Smith for example wrote:

               

              What's going on? How can I make Photoshop to use at least those 3072 MB? Is there a trick to make it use the full 4 GB which it should be able to see?

               

              You're running a 32-bit application and the max is slightly less than 4 gigs minus ram for the running application. The only way to use more of the ram would be to upgrade to PS CS5 and run as a 64-bit app. The improvement in performance of CS5 would be noticable if you are working with large images.

              • 4. Re: Photoshop CS4 not using RAM
                Chris Cox Adobe Employee

                While the address space available to a 32 bit application is theoretically 4 Gig, the reality is that the OS takes a lot of space, plus the space taken by loading the application binaries and OS library code. That leaves around 3 Gig available.  After working for a while, the address space gets fragmented -- 1 Gig total might be available, but it's scattered in 1 Meg pieces around the address space so you can't really allocate a large buffer.  And as you work, the OS consumes more address space for it's purposes and Photoshop frees up space as needed.

                 

                If Photoshop uses all the available address space, then the MacOS code will start crashing because it assumes that it will always be able to allocate more memory.  And many third party plugins assume that they'll be able to allocate large chunks of memory, and tend to crash when they can't.  So Photoshop can't safely use 100% of the available address space (hence the preference).

                 

                All in all, what you're describing sounds normal for a 32 bit application.