Photoshop RAM limited to 3072 MB, but my MP has 10 GB of RAM?

Discussion in 'Design and Graphics' started by DHart, Sep 22, 2008.

  1. DHart macrumors 6502


    Jan 17, 2008
    Just wondering if anyone here can help me figure out why Photoshop CS3 on my new MacPro is only seeing 3072 MB of "Available RAM" on my new MacPro which has 10 GB of RAM installed?
  2. DHart thread starter macrumors 6502


    Jan 17, 2008
    Just found that Adobe limits to 3 GB. But there's a workaround on MacOSHints:

    Work around Photoshop's 3GB RAM limit
    Fri, Jul 18 2008 at 7:30AM PDT • Submitted by Anonymous

    With RAM prices dropping so fast, it seems a shame that I can't really use more than 3GB of memory for Photoshop. As a 32 bit application, Photoshop CS3 can only "use" 4GB of real memory -- a 1GB chunk for the application, leaving a potential 3GB of real RAM available for Photoshop to use for my images. For anyone with 8GB or more of memory, here's an old concept that tricks Photoshop into using as much memory as you want.

    Remember RAM disks from OS9? The feature is available in the command line in OS X. By creating a RAM disk, and having Photoshop use that as the first scratch disk, you'll speed up Photoshop as long as you have enough real memory to do it. For my test, I allocated 3GB to Photoshop in its prefernces (real memory usage), and then created a 2GB RAM disk.

    The Terminal command to create a 2GB drive is:
    hdid -nomount ram://4194304
    The number is the number of 512 byte blocks in your RAM disk. The example above creates a 2GB disk, so a 4GB drive would be 2x that number, and a 1GB drive would be half that number, and so on. Once the disk is created, format it with Disk Utility. Then configure Photoshop to use the RAM disk as your first scratch disk. As soon as CS3 hits the 3GB memory barrier, it starts using the RAM disk as "memory" first. Remember, it will be "swapping" memory pages in and out of the 3GB memory set, but this is still better than swapping to and from a hard drive.

    I created a 4.5GB file in Photoshop, and was pleased to see almost no disk activity on my real drive, but my RAM drive was full during my test.

    Note: This really only helps someone with 8GB or more of memory running CS3 a lot. For example, if you had 16GB of memory, you could create an 8GB RAM disk, and then allocate 3GB in CS3, effectively having Photoshop "use" 11GB of real memory before hitting the disk. Also note that RAM disks are not quite as fast as regular memory access native to an application, but they are much faster than having CS3 swap to your hard drive.

    While it takes some steps to get this configured, I thought there might be some people out there interested in improving how CS3 uses real memory, since there is no 64-bit version yet.
  3. ChrisA macrumors G4

    Jan 5, 2006
    Redondo Beach, California
    Are you really trying to edit photos that are larger than 3GB? If your images don't fill 3GB then using more RAM would be a waste. But actually you are using more than 3GB. Mac OS X is using the other 4GB or so of space as a disk cache.
  4. DHart thread starter macrumors 6502


    Jan 17, 2008
    Chris... the images I edit are about 36 MB in size when I open them and I know that PS often inflates that considerably with layers, history states, and such. And I usually open a complete client order of about 12 to 20 images at a time to edit. So 3 GB (1 for the program and two for images?) is probably fine.

    I just made a 2 GB RAM Disk to add to the 3 GB of RAM giving me a total of 5 GB RAM for Photoshop (of my 10 GB total) so I'm very happy now.

    Occasionally I work on multi-layered files of around 175-200 MB which with history states and such could amount to significant RAM usage.

    I'm loving this new MacPro and all the RAM!!!
  5. GoCubsGo macrumors Nehalem


    Feb 19, 2005
    This is something I didn't know about, the RAM limit. Guess never having more than 2GB for a while I never cared. :)
    Thanks for this post DHart.
  6. jerryrock macrumors 6502


    Sep 11, 2007
    Amsterdam, NY
    A ram disk isn't going to help your system with CS3. It is not necessary to create a ram disk because Photoshop CS3 and OSX automatically use your available ram as scratch disk.

    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. You can see the actual amount of RAM Photoshop can use in the Let Photoshop Use number when you set the Let Photoshop Use slider in the Performance preference to 100%. The RAM above the 100% used by Photoshop, which is from approximately 3 GB to 3.7 GB, can be used directly by Photoshop plug-ins (some plug-ins need large chunks of contiguous RAM), filters, and actions. If you have more than 4 GB (to 8 GB), the RAM above 4 GB is used by the operating system as a cache for the Photoshop scratch disk data. Data that previously was written directly to the hard disk by Photoshop is now cached in this high RAM before being written to the hard disk by the operating system. If you are working with files large enough to take advantage of these extra 2 GB of RAM, the RAM cache can increase performance of Photoshop.
  7. DHart thread starter macrumors 6502


    Jan 17, 2008
    jerryrock.... thank you for that information. It's good to know that my 10 GB of RAM will boost my Photoshop performance even though I can only set about 3 GB in the Performance settings window. It sounds like the RAM DISK solution specified in MacOSHints was designed for an earlier Mac OS that didn't automatically assign scratch disk needs to available RAM before going to the hard drive.
  8. payne macrumors newbie

    Sep 30, 2008
    Another Question!

    Just got my Mac Pro with 24 gigs of RAM. My Raw camera files are about 70-80mb each and usually have a minimum of 10-20 open, sometimes more if the files are on different media drives from the same project. Would it be beneficial to make a RAM disk even though it recognizes up to 8gigs? I suppose it couldn't hurt to beef it up. What would you suggest making the RAM disk size?



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