Basics4Mac - Making Sure You Have Enough Hard Drive Space

Don't get caught short

Available space
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I was working with a client recently who was getting an error message that her hard disk was almost full. When we checked it out, she had only about 150mb of space left. What does that mean and why is it important?

Mac OS X needs space on your hard drive often called "scratch disk." It uses that space as temporary storage when it runs your applications. Generally speaking, you should have about 5GB to 10GB free on your hard drive at an absolute minimum. Unfortunately, Mac OS X doesn't start to complain until you have far less space than that.

You can tell when your Mac is getting low on scratch disk space because you will find that your applications are crashing regularly and your are getting the "Spinning beachball of death" more often than normal.

You can tell how much free space you have left on your hard drive by going to the Finder and selecting your hard drive from the left pane. Then look at the bottom of the Finder window and you will see "X items, Y available." The number of items isn't important but the amount of space is.

So how much is a GB? It is short for gigabyte and is roughly 1 million bytes. And I bet that means nothing to you.

With your hard drive still selected in the Finder, choose Get Info by either right-clicking the hard drive icon or clicking the gear in the tool bar. Among the other info you will see are Capacity and Available. Both are numbers followed by GB.

For the sake of simplicity, consider the Capacity and Available values as whole numbers and then look at them in relative terms. 100GB is more than 75GB. The more GB capacity you have the more you can store on your hard drive. As you add data to your hard drive, the amount of available GB goes down. And down. And down. When you get it down below 10GB or 5GB, that is when you start having trouble.

If you let things go too long and get below 1GB, then the Finder starts to report your available space in MB. A MB (megabyte) is about 1/1000 of a GB. So my client's hard drive that had 150MG available had just a tiny fraction of the minimum amount of space required for Mac OS X to be happy. It is no wonder that all her applications were crashing.

So what do you do when your hard drive fills up? Well, you have to move things off the internal drive to either a disc or another hard drive. Movies and photos are probably your largest culprits. If you have a huge iPhoto library, you might consider moving the whole library to an external hard drive. You can find detailed instructions for that here.