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Performance Boost From Setting Different amounts of Disk Cache System 8.1 and 8.0

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The graphs below represent a performance comparison between different Disk Cache settings Disk Cache is set in the Memory control panel. Testing was done using MacBench 4.0 on a 9500/200 with 96MB of RAM and OS version 8.1 installed. Hard drive was not updated to the new HFS+ standard. MacBench profiles popular software programs such as Adobe Photoshop, Word 6.0 and QuarkXpress among a variety of others and applies these profiles to the various subsystems being tested. See this description of what MacBench tests and how. Longer bars equals faster performance.


Note: MacBench probably makes greater use of the disk cache than most most applications. These results therefore in all likelihood give an accurate assessment of the benefits of the disk cache but also an exaggerated one in as far as general computer use is concerned. It would appear from these scores that there is little benefit from setting the disk cache above 1MB and diminishing returns above 512K. I would treat these results as indicative rather than definitive. MacSpeedZone welcomes your comments on these results.

Stopwatch Tests

The results below measure the percentage of time taken to relaunch a application or file. During a relaunch certain information is taken from the Disk Cache rather from the drive thus speeding performance. Results represent the performance improvement over a base 96K Disk Cache which receives 100%. Shorter bars equal better performance.




Comparison When Speed Double 8.1 Is Installed - Disk Cache Set To 1MB


From the Speed Double 8.1 Read Me

What To Set The Disk Cache If You Have OS Version 8.0 Installed

And If You Have Speed Double 8.0 Installed

Note: These results seem to indicate that a higher disk cache around 1MB is advisable under System 8.0 for optimal performance


Note from Patrick McClaughry of Apple Computer

As a contributor to the Finder present in Mac OS 8 and 8.1, I think you will find the rate at which large folders (that is, folders with more than several hundred items) open in the Finder is dependent on the disk cache as well. Our testing during development showed that, with a cache setting of 96K, we often got performance an order of magnitude slower than with the cache at 1M. The reason is a change in the way the Finder reads catalog information from the disk. This fact was mentioned in the Mac OS 8 tech notes.

Regards, -Patrick McClaughry Former Tech Lead, Mac OS 8 Finder


Note From: Seth B. Noble <>

The cache tests you showed are interesting, but I think there's more to the story.

A more extensive use of disk caching is to run a web browser like netscape and turn off auto-loading of images. Then navigate through image intensive pages that have been cached and see how long it takes the browser to load the pages.

I should first note that Netscape has extremely poor throughput when reading from disk (it seems to pass the data through the same high- overhead streams that it uses for networked data). But I have observered some very non-intuitive behavior when the system disk cache is set high.

When the system cache is at 4 Mb, Netscape will experience occasional long pauses when reading from its own disk cache. When the system cache is set to 2 Mb, the pauses seem to go away and throughput when reading from the disk is generally faster. (This was tested with Navigator 4.0.1a and

This and your stopwatch tests would suggest that large caches can actually reduce system performance, sometimes dramatically. That could be due to search overhead in the way the system locates data in a large cache. I would speculate that the code used to organize and search the system cache needs to be optimized.