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Rightsizing your mac application memory

By Kristin E. Nelson

Machine lockups, warnings about not enough memory to open applications, or problems opening large or complex documents can be symptomatic of a low memory situation. If the amount of installed memory (RAM) on your Macintosh is sufficient to handle your computing needs, you can use this memory more efficiently by rightsizing the memory allocations to the applications you use.

Before experimenting with different memory allocations, consult each application's user manual and other information available from the software developer for memory usage tips. Arriving at the proper memory amounts for your applications and work style requires some trial and error but can be well worth the effort.

About This Macintosh

The window displays the following information:

• Built-in Memory. The amount of RAM physically installed in the machine.
• Largest Unused Block. The largest block of memory available to launch another application.
• Total Memory. The RAM (physical + virtual memory) available to the Macintosh. (Note: This item displays only when virtual memory is on or when a memory utility, such as RAM Doubler, is installed.)

Get Info

The Memory Requirements section of the Get Info box provides the following information:

• Suggested size. The memory allocation recommended by the application's developer.
• Minimum size. The smallest unused block of memory that must be available for the application to launch.
• Preferred size. The maximum RAM allocated to the application if a block larger than the minimum size is available. (Note: MacOS versions prior to 7.1 used the single setting "current size" in place of the minimum and preferred size settings.)

Rightsizing

What you change in the Get Info window depends on the situation you want to correct.

• If the application freezes often or if you need to load large or complex documents that require additional memory, try increasing the application's preferred size. If extra memory is available, it will be allocated to this program. (Note: When increasing application memory, a good starting point is to increase by 50 percent. For example, set an application currently using 2,000 KB to 3,000 KB).

• If you do not want to run the application with anything less than a specified amount of memory, increase the minimum memory setting as well. For example, if you discovered that for your purposes an application requires a certain amount of memory, change the minimum setting to that amount. (Note: Use the rule of thumb above as a general guideline for increasing the minimum memory setting.)

• If you find that an application allocates much more RAM than you typically use or if you don't have much memory left in the largest unused block to launch the application, try reducing its preferred and/or minimum memory allocations. Be careful! Lowering the memory requirements may cause more frequent low memory situations and application crashes.

Other memory tips

• If you've opened and closed applications throughout the day, your available memory may be fragmented into a number of smaller chunks. The largest unused block is the largest of these memory chunks and may be insufficient to open another application. Exiting all open applications, or better yet, restarting your machine, will clear out the memory and should provide a larger unused block of memory for your application.

• If your Macintosh has a 68030 CPU or better or a 68020 CPU with a PMMU chip, use virtual memory to provide a memory boost by increasing your total memory and thus the largest unused block. To set virtual memory, which uses space on your hard drive as additional RAM, open the Memory control panel. Turn Virtual Memory on and then click the up or down arrow (shown below) to set an amount for total RAM (i.e., physical RAM + virtual RAM). This amount will be taken away from available hard drive space so make sure you can afford to lose this storage space. Be aware, however, that virtual memory creates overhead by accessing the hard drive and can slow machine performance in certain situations.
  

• On a Power Macintosh, turn on virtual memory to reduce the memory requirements of native applications (those designed to run on a Power Macintosh). Increasing the memory by 1 MB provides the benefits of Power Macintosh memory management without the additional overhead of higher settings.

• If you use virtual memory on any Macintosh, do not exceed twice your physical RAM and keep the amount reasonable. Increasing your RAM by 50 percent is generally a reasonable working amount.

• Some software applications work better with real (physical) memory as opposed to virtual memory. A number of applications (including Adobe Photoshop) use their own memory management scheme. In these cases, using virtual memory decreases the performance of the application.