Memory Allocation problems

You need to do a little reading:

http://www.macosxhints.com/article.php?story=20010613140025184

http://developer.apple.com/documentation/Performance/Conceptual/ManagingMemory/i ndex.html

http://developer.apple.com/documentation/Performance/Conceptual/ManagingMemory/A rticles/AboutMemory.html

In fact the "free" memory figure you see only refers to RAM that has not been used. "Inactive" memory is RAM that has been used but is no longer in use and is available for other applications. The total amount of "available" memory is the sum of inactive and free. You know you are running out of memory and relying entirely on VM when you start to see positive instantaneous pagout figures when you run the command "top" from the Terminal. If you see a positive Pageout number in parentheses, then you have a RAM shortage problem.

Your system can become slower over time for a number of other reasons, but first you have to specify what the measure of "slower" is. If you are talking about Safari getting slower, this has nothing to do with VM and everything to do with Safari itself. If you are talking about overall system slowdown it may be because you don't leave your computer on 24/7 and the Unix maintenance scripts are not running. Hence your temp, log, and cache files are getting too large. Install the shareware utility Macaroni to resolve this problem.

Other possible problems can arise from virus software that is incompatible with Tiger and hogs CPU time. Immediately after installing Tiger Spotlight begins to index your hard drives. This could take hours during which time the computer will be sluggish. If you open the Activity Monitor and click on the CPU tab, you can observe whether any particular process is hogging the CPU.

Most complaints about RAM or memory related slowdowns come from users who do not know a thing about memory management in OS X. Repairing permissions is not a memory management solution or maintenance routine.

I totally agree with Kappy. I'll only add that my interpretation of "free" memory on a healthy system is to take the total physical RAM installed on your system (1.5 GB for the top post) and subtract the amount of "wired" memory from this. The result is the amount of physical RAM available to any application, instantaneously.

Activity Monitor will show you the amount of "wired" RAM used. Its usually minimal.

Now, is that physical memory in use before an application requests it? You bet.

RAM that is not in use is a total waste of resources.

The fact that Repairing Permissions frees up memory indicates that your system is not healthy, for some reason or another.

I'm curious what the basis is for you assumption that the memory tagged as inactive is not available for other applications to use. If applications were reliying solely on VM you would start to hear a lot of drive thrashing and note a dramatic slowdown in application behavior.

I can launch Disk Utility an run Repair Permissions and note no significant change in anything in top other than the additional overhead of running DU. The amount of inactive RAM before and after is just about the same.

The reason pages free up when running Disk Utility is simple; enough memory is required to run the utility that inactive pages have their contents swapped out through normal pager activity, resulting in them being added to the free list.

As mentioned above, you can read more about Apple's memory management here; to quote it in brief:

When the number of pages on the free list falls below a threshold (determined by the size of physical memory), the pager attempts to balance the queues. It does this by pulling pages from the inactive list. If a page has been accessed recently, it is reactivated and placed on the end of the active list. If an inactive page contains data that has not been written to the backing store recently, its contents must be paged out to disk before it can be placed on the free list. If an inactive page has not been modified and is not permanently resident (wired), it is stolen (any current virtual mappings to it are destroyed) and added to the free list. Once the free list size exceeds the target threshold, the pager rests.

Have a look at this knowledge base article:
http://docs.info.apple.com/article.html?artnum=107918

Here's the last paragraph:
"What does all this mean?
This means you shouldn't worry when the Free memory is low. The only time Free memory should be high is right after the computer starts up. As you use applications or services, memory is used and transitions to Inactive. Applications that need more memory will take from the Inactive, but the Inactive is there just in case you need it again. If the combination of Free and Inactive is very low, then you might need more memory." (emphasis added)

HTH!

Apple should add an "available" field in the Activity Monitor.