How to Change Memory Allocations for Macintosh Programs (141682)


The information in this article applies to:

  • Apple Macintosh System Software
This article was previously published under Q141682
NOTE: This article applies to Mac OS versions earlier than Mac OS X (Mac OS 9.1 and earlier).

SUMMARY

On a Macintosh computer, you can manually adjust the amount of memory the system allocates to a program. However, the amount of memory that the program actually gets depends on several factors. One of these factors is the amount of memory available in the largest unused block. If the system is low on memory in the largest unused block, the program may not start or it may quickly run out of memory when you try to open a file or perform actions such as copying or pasting data.

MORE INFORMATION

Programs on a Macintosh have two memory settings that can be adjusted: Minimum size and Preferred size.

The Minimum size setting indicates the smallest amount of memory that will be requested by the program when it is started. If the largest unused block of free System memory is less than the setting for the program's Minimum size, the program will not start.

The Preferred size setting indicates the total amount of memory requested by the program. The system will give as much of the largest unused block to the program as it can, up to the amount specified for the program's Preferred size.

In addition to preferred and minimum memory sizes, programs have a third memory requirement called "suggested size." Suggested size is a number that is set by the developers of your program and cannot be adjusted. Suggested size is the amount of memory that the program developers felt the program would run best with: you should always try to set the Preferred size to a number at least as large as the suggested size.

To better understand the differences, see the following examples.

Example 1

Minimum size: 2048K
Preferred size: 4096K
Largest unused block of System memory before starting program: 1800K

In this case, the program will not start because the largest unused block of free system memory is less than the minimum size for the program.

Example 2

Minimum size: 2048K
Preferred size: 4096K
Largest unused block of system memory before starting program: 3000K

In this case, the program should start, but it will only be allocated roughly 3000K of memory. It will try to get as much as it can, but it can only get up to the amount in the largest unused block of system memory.

Example 3

Minimum size: 2048K
Preferred size: 4096K
Largest unused block of System memory before starting program: 8000K

In this case, the program should start, and it should get all of the 4096K requested of the system. It probably won't be using all of this 4096K, though, as there is usually quite a bit of extra room for your personal data files to be loaded into memory by your program.

Note, in all cases, the largest unused block of system memory may be much lower than you think because of memory fragmentation. This article will not discuss memory fragmentation. However, note that to clear up most problems with memory fragmentation, shut down all running programs and restart your computer.

How to Determine Unused System Memory and Program Memory Requirements

In order to configure memory allocations for various Macintosh programs, you must know where the memory settings are located.

To determine the largest unused block of system memory, click About This Macintosh on the Apple menu.

NOTE: If you do not see "About This Macintosh", but instead see "About <program name>", then click "Hide <program name>" on the Application menu and then repeat click About this Macintosh on the Apple menu again.

In the About This Macintosh window, you should see the version number of the System Software. You should also see the amount of memory taken up by the System, a list of currently running programs, the amount of memory allocated to each program, and a number for the largest unused block of system memory. If the sum of all of these memory amounts is much less than the number that is shown for Total Memory, you probably are running into a situation of memory fragmentation.

To set the memory requirements for your program, do the following:

  1. If your program is running, save any of your files and quit the program.
  2. Locate the icon for your program on your hard drive and click once on it to select it.

    NOTE: You must locate the actual program icon rather than an alias for the program (you cannot do the next steps from the icon for the alias).
  3. With the program icon selected, click Get Info on the File menu.
  4. In the "<program name> Info" window, click the edit box for either the Minimum size or the Preferred size, delete the current number, and enter the new amount.
  5. After you have made changes to either the minimum size or the preferred size, or both, close the window and restart your program.
You do not have to restart your computer for the above changes to take effect.

For additional information about Memory Requirements on a Macintosh, please see the following article(s) in the Microsoft Knowledge Base:

127084 Power Mac Applications Require Less RAM with Virtual Memory

120506 How Virtual Memory Works on a Power Macintosh

139406 MXL5: Macintosh System Memory Requirements

Modification Type:MajorLast Reviewed:4/22/2001
Keywords:KB141682
©2002 Microsoft Corporation. All rights reserved.