[perfessor101]

I recently read a supposedly authoritative source that said there is a very big difference in Panther performance between a machine with 512 MB RAM and 640 MB. That source recommended 640 MB as the "sweet spot" although performance continues to improve all the way up to 1 GB and more. I cannot verify that scientifically, but from my experience I would be inclined to believe that is true.

Perhaps this will help you understand OS X memory usage a little better:

1. all memory in OS X is "virtual". Some of that virtual memory is in RAM, some in system and application files on the hard drive, and some may be in swapfiles
2. Wired RAM is memory that is pernamently "locked" by the OS and cannot be made inactive or moved to swapfiles. It must be there for the operation of the OS
3. Active RAM is memory that is currently in use by either the system or an application.
4. Inactive RAM may be thought of as a first stage swapfile. It contains instructions and data that are not currently in use within the OS or an application, but is left in RAM in the event it is needed again. If more Active RAM is needed, the Inactive RAM will be reassigned and if it contains data for a currently open application, that data will be rolled out to a swapfile. Otherwise the memory will simply be overwritten.
5. Free RAM is just that. It is RAM that is currently not mapped into Wired, Active, or Inactive RAM. If more Active RAM is needed, the Free RAM will be the first to be remapped into Active status.
6. Swapfiles are used to contain data being used by currently open applications for which there is currently no room in either Active or Inactive RAM
7. System resources, fonts, application files, frameworks (shared libraries) are mapped into the virtual memory address space for each application whether they are in Wired, RAM Active RAM, Inactive, RAM, or in files on the HD, but these resources are never placed in the swapfile(s) because they are already available on the hard drive and there is no point in duplicating the code.
8. Pageins occur anytime something is moved into Active RAM whether that is from Inactive RAM, the swapfile(s), or another file on the hard drive.
9. Pagouts occur anytime anything is moved out of Active RAM which includes mapping into Inactive RAM, as well as writing to a Swapfile. Only data is ever written to the hard drive since instructions are already on the hard drive.

All in all this is a very efficient use of memory. It also has the benefit of providing an almost invulnerable wall protecting the operating system and each application from inadvertent intrusion by ill behaving code. This is one of the "secrets" of OS X stability.