Reader Matthew Mitchell feels the walls closing in. He writes:
I have a 17-inch MacBook Pro with a 320GB hard drive. (Formatted it has 297GB, but who’s counting?) I’m down to 70GB and I heard that a full hard drive is a slow hard drive. I went looking for files to delete and found a fair few that were either hardly ever used or never used. Are there any secret locations on my hard drive that large and disposable files could be hidden?
There’s lots to talk about here.
Let’s start with the capacity of your hard drive. For just about ever, hard drive manufacturers have defined a megabyte as 1,000KB. The Mac OS defines a megabyte as 1,024KB. It’s for this reason that a 320GB drive (using the 1,000KB measurement convention) appears to have much less capacity, because it’s being measured by the OS using the 1,024KB definition. It’s been reported that this behavior will change in Snow Leopard so that OS X 10.6 will show a 320GB hard drive having exactly that capacity.
As for a full hard drive slowing down your Mac, it’s true. OS X uses your hard drive to swap files out of RAM and if there’s very little room to do that, your Mac needs to work harder at the job and therefore slows down. Note, however, that at 70GB your 320GB isn’t there yet. Continue to leave 10 to 15-percent of your hard drive free and you should be in fine shape.
Now, let's turn to lurking files and folders. In this regard it’s worth your while to download a copy of The Omni Group’s free OmniDiskSweeper. This utility will tell you how much space is consumed by folders and files on your Mac. When you find something you believe you can do without, simply highlight it and click on the Delete button in the bottom-left corner of the window.
Good places to start looking are in the /Library and ~/Library folders. For example, look in the Audio folder within the /Library folder and you’ll find an Apple Loops folder that holds GarageBand’s audio files, which take up many gigabytes of storage. If you don’t use GarageBand, this folder can go. Similarly, iDVD’s themes (found in /Library/Application Support/iDVD) take up a couple of gigabytes of storage that you can free up if you never touch iDVD.
Because it doesn’t go without saying for everyone, allow me to offer a couple of safety tips. First, don’t throw out items in the System folder unless you really, really, really know what you’re doing. And, more generally, don’t toss out files and folders stored elsewhere on your Mac unless you know the purpose they serve. Doing so could land you knee-deep in the soup.