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View Full Version : Virtual Memory, Macbook vs. Powerbook G4 (WTF!?)




akindy
Feb 28, 2008, 11:21 PM
So I've got a 2.0 GHz, white MacBook with 1gb ram, and a G4 Powerbook 1.67 with 1gb of ram. The major software difference between the two is the OS, the MacBook is running Leopard. So, I noticed the MacBook started to lag a little from when it was new, so when I upgraded to Leopard I did a clean install. Still noticed the lag so I checked my ram, and here's what I got:

The Powerbook was running the same exact apps (iTunes, iChat, iPhoto, Safari) as the MacBook, and even after loading dashboard on the Powerbook it still used only 500mb of ram and 4.45gb of Virtual Ram. The MacBook was using 615mb of ram and 32 GB OF VIRTUAL MEMORY?!? Wtf? I thought it might just be counting space set aside, but I checked the apps and adding all them up is about 32gb. They both have the same iPhoto library yet the powerbook's only took up 240mb of virtual ram and the macbook's over 1000mb.
I realize there are some slight differences (different iChat, spaces was running) but why in gods name would it make the MacBook use almost 7 times the amount of virtual ram! Help!



abijnk
Feb 28, 2008, 11:41 PM
What are the hard drive sizes of the two notebooks?

akindy
Feb 29, 2008, 08:32 AM
They both have 80gb, but the macbook is sata and the powerbook is ata.

Cromulent
Feb 29, 2008, 08:37 AM
Virtual memory does not mean much. Just ignore it.

What you want to look for is the amount of RAM which is being used and the number of page outs you are getting.

robbieduncan
Feb 29, 2008, 08:47 AM
It's not using 32GB of virtual memory. In fact it's using 0 (as can be seen by the number of pageouts being zero). The total VM size is currently 32GB, but it's mostly not in use so no page files have been created on the disc.

akindy
Feb 29, 2008, 08:57 AM
So macbook's have to set aside six times the amount of virtual memory as powerbooks? Or is it Leopard that has to?

robbieduncan
Feb 29, 2008, 09:02 AM
So macbook's have to set aside six times the amount of virtual memory as powerbooks? Or is it Leopard that has to?

VM size is not the same as virtual memory. Neither of the screen shots show any pageouts so in both cases all code and data for running processes is in system RAM.

The VM size is the total size of the theoretic VM size allocated to all currently running processes: it's not the amount of RAM, physical or virtual in use.

gnasher729
Feb 29, 2008, 09:26 AM
So macbook's have to set aside six times the amount of virtual memory as powerbooks? Or is it Leopard that has to?

As an analogy: Lets say you have three credit cards.

The first one is overdrawn by $1000. That 1000 is a real number, you owe them real money.

The second card has a credit limit of $10,000. That number doesn't mean anything until you go overdrawn. You don't have to pay anyone any money because of that credit limit.

For the third one, the bank manager has a form where he can fill in your credit limit, and that form has space for a six digit number. So he can give you a credit limit up to $999,999. That number means nothing at all. And that is about how meaningful the "Virtual Memory" numbers in Leopard are.

But I noticed that you actually had free memory (green in the display). Green means: This memory has no use at all at the moment. Blue (inactive) means: This memory is used for caches, it might be useful for something, but the system can get rid of it at any time at no cost if something really _needs_ memory. As long as you have green memory, there is no need to worry at all. If you still have blue (inactive) memory, you're still fine.