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Punkyclown's picture
Joined: 2017 Nov 9
Memory management on Classic Macs

Hi All, I have added 24 mgs of ram to my PowerBook 1400c for a total of 56 mgs
or ram. I have turned off Ram Doubler and set Virtual men to 8 mgs . Which
now shows Virtual memory at 64 mgs. This is a little confusing to me, after a
restart it shows my total ram at 64 mgs? Since what I'm reading about my particular
Mac 64 mgs should be more than enough to run any software I need or want to on
that machine. I thought I would go with that to see how it worked. So is this a smart
or correct move or should I put Ram Doubler back on and run at 112 mgs. If I was using
a SSD than I think this would be fine, but since I'm not why do I want my Mac spending
time writing and retrieving from the Hard Disk? Any advice would be helpful.
Thanks, Brad Hansen


sfp1954's picture
Joined: 2013 Dec 29

Virtual memory must be set equal to, or greater than, real memory. It cannot be set to less.
So in your case you can set it at anything from 56 to 128 to ???. It depends on how much disk space you want to give up to virtual memory.
The big question is which is more stable for your operating system and platform.
Apple's virtual memory or Ram Doubler?
Personally I never use either unless an application demands it, so someone else will need to comment on that angle.

Joined: 2011 Jul 21

I programmed for awhile with Digital Equipment Corporation's VAX (Virtual Architecture eXtended) computers. They referred to virtual memory usage as "paging". When an application began to "page" (copy the contents of RAM to disk and replace it with another chunk of stuff (512 bytes)), the app would quickly grind to a halt. We were given classes on how to avoid "paging" which typically revolved around using arrays of 512 bytes rather that 513 bytes as an example).

I learned from that experience that virtual memory was something that I should avoid.


Punkyclown's picture
Joined: 2017 Nov 9

I apprettiate the advise, but when I run 8.6 without Virtual Memory on, the System
take 20.2 mgs at startup. When it is on it takes 11.2, so since I only have 56 mgs
it sort of defeats the purpose of trying to run larger programs like Cassilla. And being
able to run multiple programs at the same time. Does someone know weather Apple
VM or Ram doubler are the preferred way to run Virtual memory?
Brad Hansen

Knez's picture
Joined: 2010 Feb 11

RAM Doubler only uses unused but allocated RAM for other applications needing it more.

Say you have an application that has "max ram" set to 10MB but currently only uses 2MB. RAM Doubler let's other applications use the unused 8MB of RAM since it's just there doing nothing at the moment. When the application lending the RAM needs it, RAM Doubler gives it back. This leads to horrible crashes if you are using applications that need more or less all your physical RAM (like Classilla).

My advise would be to go with the built in Virtual Memory to gain some actual usability, even if it's somewhat slow (since it's "real" virtual memory, as in a file on your harddrive being used as RAM)