OS X and RAM--How Fast Is It?

Mac OS X runs faster if one has more RAM. But how much RAM does one need to get all one can get from Mac OS X 10.0.4?

We subscribe to several list servers and people frequently ask how much RAM they need for Mac OS X. The usual advice is "...as much as you can afford...." While this is a good rule to follow, and an easy one at that now that RAM is so cheap, most advice has been 512 MB and more if one works with large images.

We decided to put our Power Mac 7300 upgraded with a 400 MHz G3 CPU through a series of tests to determine the break point, i.e. how much RAM is enough. We were aided in conducting the tests by a sale on the older style FPM 2K 128 MB RAM chips that our 7300 (and all PowerSurge Macs 7300-9600) uses. OWC had them for $45 each and we picked up two to augment the existing 192 MB of RAM. We recently posted a How Fast Is It? test with OS X on the upgraded 7300 with that amount of RAM.

For the test we launched a Classic mode application (Netscape 4.77), a Carbon app (Acrobat Reader 5.0) and a Cocoa app (OmniWeb 4.0.1) and timed the first and several successive launches. We also timed the Classic mode (Mac OS 9.1) start up and the period to scroll the 144p Virtual PC 4 Manual that is full of color images in Acrobat 5.0.

Here are the results:

Average Times in Full Seconds (First Launch in Parentheses)

Application	64 MB	128 MB	256 MB	448 MB
Classic Mode	135	79	60	59
Netscape 4.77	10 (29)	7 (15)	7 (9)	7 (9)
Acrobat Reader 5.0	35 (13)	7 (17)	7 (13)	7 (11)
OmniWeb	25 (59)	16 (26)	16 (23)	16 (23)
Scroll VPC Manual	93	90	88	87

For these actions, 256 MB appears to be enough RAM on the 7300. There is still a minor gain in two operations moving from 256 MB to 448 MB but the speed gain is not worth it. Of course, if one processes large images even more RAM than 448 MB would be beneficial.

Apple has stated that Mac OS X will run on 64 MB of RAM but 128 MB is needed if one runs Classic applications. We think 128 MB is too little and would recommend at least 256 MB. At 64 MB just clicking on pull down menus in the Finder caused the hard drive to grind away using virtual memory. Closing applications took almost as long as opening them with the attendant grinding of the hard drive. Some heavy virtual memory usage occurred with 128 MB but none with 256 MB. A good way to tell if one needs more RAM is if the hard drive grinds during operations that normally do not involve reading from and writing to the hard drive.

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