Mac OS: Minimizing Memory Fragmentation

Symptom

A dialog box appears with the message that there is not enough memory to continue even though you are sure your computer has plenty of memory. At other times, the Largest Unused Block information in the About This Computer window does not change even after quitting an application program.

Solution

Memory fragmentation is similar to hard disk fragmentation, but files stored on a disk can easily be broken up into fragments if there is not enough contiguous space on a disk. Programs that are loaded in memory, however, cannot be fragmented, and thus need a contiguous area of memory. Your computer may have several unused blocks of memory mixed in with the used blocks of memory, but Mac OS can make only a single unused block available to a program.

Memory becomes fragmented more frequently if virtual memory is turned off.

To defragment memory, use one of the following techniques:

Technique 1

1. Quit all open applications and desk accessories.

2. Open the applications you need to use.

Open applications appear in the Application menu. To quit an application, choose it from the Application menu, and then choose Quit from the File menu. The Largest Unused Block in About This Macintosh increases as more contiguous memory is made available, but it doesn't necessarily increase with each program you quit.

Technique 2

Restart your computer.

To avoid fragmentation again, carefully plan the order in which you open and quit programs:

1. Open first the applications and desk accessories you are least likely to quit.

2. Open last the applications and desk accessories you are most likely to quit during a work session.

By opening and closing applications and desk accessories this way, the memory you free up is contiguous with the rest of the Largest Unused Block. When you quit programs in random order, you are likely to have fragmented memory.

Other Solutions

• On a Power Macintosh computer, you may experience less memory fragmentation if virtual memory is turned on. For more information see article 16889: Power Macintosh: Turn on Virtual Memory for Best RAM Usage
• Deselect "Load only when needed" in the TCP/IP control panel. For more information see article 19484: Open Transport 1.1: Memory Fragmentation
• You should update to system software version 7.5.5 or later, which is available from http://www.apple.com/swupdates/ . For additional update information see article 20081: System 7.5.3: What Updates Do I Need for System 7.5.5?