Disk Space Help

Take a look at DiskInventory X (will not work in Mac OS X 10.7 Lion), OmniDiskSweeper, JDisk Report or GrandPerspective to see where your HDD space went to.
What is this "Other" in the storage tab? What is eating up my space? by theSeb

Btw, "memory" is not the same as "hard drive capacity":
What is Computer Memory? RAM vs Hard Drive
RAM vs. Hard Disk
It is recommended, to have 10 to 20 % of the HDD's capacity unused.

 

You're referring to drive space, not memory. Memory is RAM. You may have better success in attracting responses to your thread, and you'll make your thread easier to find for those browsing the forum for the same answers, if you follow this tip.


For space issues, there are a few things you can try:

• Begin by restarting your computer as a first step. This sometimes resolves issues.
• For Time Machine users on Lion, space may being consumed by Time Machine local snapshots, which can be disabled.
  OS X Lion: About Time Machine's "local snapshots" on portable Macs
• Search with Finder to see if the space is being consumed by a very large file or several large files. Adjust the 50GB in the illustration to whatever size you deem appropriate.
  
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• Use OmniDiskSweeper, JDisk Report or GrandPerspective to see how space is being used on your drive. Some of these apps may show more detail than others, so try several.

 

That has never been true. Yes a hdd gets consistently slower the more filled up it is because it startst writing at the outer tracks which are fastest sequentially and ends at the inner, but that has nothing to do with smoothness. You only notice this in big file transfers.
It operates smoothly until it is almost completely full. If there is less than 2-3 GB drive space left gets bad and with only a few hunderd MB it can even run into some errors with certain apps.
There is absolutely no reason to use less than half of the diskspace. If you get into the single digit GB left area you can start to worry about deleting stuff. <10GB.