Here's the scoop on the memory slider: Photoshop measures RAM and then subtracts a very rough estimate of how much the OS needs and how much is needed to hold Photoshop's program instructions, and calls that 100%. Photoshop can never use more than 2GB. If you're mostly working only in Photoshop, numbers from 90-95% are probably fine. By "working only in Photoshop", I mean not having other applications doing actual computation in the background. Just having other apps launched and inactive doesn't matter much. If you have lots of RAM (1GB or more) numbers in the 95% range are fine. If you have more than 2GB RAM, tell Photoshop to use 100%.
Setting the slider too low will cause Photoshop to leave memory unused that it could be using. The symptom of that is that the efficiency number (in the info box at the bottom of the document number) starts dropping. If the efficiency number is less than 95% or so, Photoshop is moving image data to and from the disk during normal operations, and should try increasing the memory slider. Setting the slider too high used to cause Windows 95/98/ME to be unstable, but that's generally not an issue with Win2K, WinXP, or MacOS X. Setting it too high -- not leaving enough memory for the OS and other active applications, will cause Photoshop's memory to be paged out by the OS. That hurts performance a lot -- even more than Photoshop moving stuff to the scratch file. One way to see if the percentage number is too high is to look at the OS performance monitor and check the paging rate (*) during typical operation in Photoshop. If you see many pagins and pageouts (more than a couple per second), the OS's VM system is moving stuff in and out from disk, so you need to reduce Photoshop's memory slider. If you can't find a point that gives you a 95+% efficiency and a very low paging rate, you need to add RAM. Remember you have to restart Photoshop after moving the memory slider for changes to take effect. (*) To check the paging rate on OS X, open a terminal window and enter "top". That's the Unix performance monitor. At the bottom of the first clump of info is a line that will look like: VM: 3.47G + 3.62M 47818(0) pageins, 107895(0) pageouts The numbers in parentheses before pageins and pageouts are the number of disk read and write operations over the last five seconds (the display will update every 5 seconds). On Windows, run Administrative Tools->Performance, and add a performance counter (right click on the graph area and pick, "add counters..."). The counter you want is in the Memory "performance object" and is called Pages/sec. We're working with the OS vendors to remove the need for the memory slider in the future. Russell Williams Photoshop engineering manager =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
