Freeing up System Memory (RAM) by Emptying the Trash

I've never heard of this problem before, but...

My guess is because there's so many items in the trash and maybe because those zipped files put themselves in the trash (maybe they are using extra memory).

That's my best guess.

Chris

My guess is that you had accessed those files, so the file system was caching the file contents until it found something better to use the memory for. However, when you empty the trash the files really go away, and thus the file system can no longer cache the contents of the file.

When looking at free RAM you need to combine BOTH the Free and the Inactive to get a more realistic estimate of RAM available for re-use.

why would the Unzip Utility/OS need to cache a file.

I can understand caching a web page,

It doesn't. The Unzip utility reads the file, and writes new files. All of this goes through the file system. It is the file system that is caching recently read or written data. When you delete a file that is cached by the file system, the file system has nothing to cache. The cache is a least recently used cache, so as you access new files (read or write) the file system will discard old cached data and cache the new stuff. If the operating system needs more RAM for other things, the file system will give up data it has cached, starting with the oldest stuff it has cached. If the OS does not need the RAM, the file system will attempt to cache as much as it can, as that avoids very expensive (in both time and Power) disk accesses. Accessing the disk is slow. Access the disk consume more power then letting it sit there idle (laptops appreciate not having the disk consume power when it does not need to).

Shouldn't the act of placing it in the trash, remove it from cashe?

The file system does not know that. The Trash is just another directory to the file system. Until the file is actually deleted, it is a real file to the file system. The Trash is a higher level concept used by the Finder. The Finder just creates a directory and puts stuff in it. The file system has no clue that this is something special.

isn't there a TTL on the cached files?

No. There is not Time To Live on the files. They remain cached until they are pushed out of the cache by other needs.

my questions is why does my machine slow down if Inactive memory is "Free Memory"?

My best guess. If some of the cached file data has NOT been flushed to disk (makes writing a file much faster if it is not forced to disk right away). However, in that case, when the RAM is needed for something else, then before the file system can release the cache it must send the unwritten new data to the disk first. And as stated above, disk access is slow. Again this is just a guess.