Power Mac Applications Require Less RAM with Virtual Memory

• Apple Macintosh and Power Macintosh computers
• Apple Macintosh System Software, versions 7.1.2, 7.5.x, 7.6, 8.0

SUMMARY

Applications designed to run on the Power Macintosh require less RAM when Virtual Memory is turned on. These same applications will use more RAM when Virtual Memory is turned off.

MORE INFORMATION

Applications written for 680x0-based machines store their code segments in resources within the resource fork. This segmentation of code allows the Macintosh to only load the needed parts of the application at any one time. This uses much less RAM than trying to load the whole application into memory.

Applications designed to run on the Power Mac store their code segments in the data fork. By default, the Power Mac loads the entire contents of the data fork into memory, where it is parsed into segments and used as needed.

When you enable virtual memory on the Power Mac, the memory manager gets "smarter" and it treats the information in the data fork similar to the way it would treat information in the resource fork. Specifically, code is loaded from the disk as it's needed. Therefore, an application built to run on the Power Mac will use less RAM when virtual memory is enabled.

For more information, please see the following article in the Microsoft Knowledgebase:

ARTICLE-ID: Q120506

TITLE:      How Virtual Memory Works on a Power Macintosh