Disk Utility

One of the cool things about Macs and OS X is their ability to be able to erase, partition, and reconfigure hard disks using tools native to the operating system. While Windows XP also has some pretty neat tools, I find Apple’s tools are a bit easier to understand and use. This discussion will address the Disk Utility tool included in OS 10.2 (Jaguar). The Disk Utility in OS 10.3 is similar but includes other functions not discussed here.

Disk Utility is in your Applications/Utility folder. Its icon looks like a hard disk with a stethoscope attached.

The Disk Utility window is divided into two parts. In the left pane is a graphical list of the attached drives and their partitions. Click on the drive or partition you want to work on. The right hand side of the window is what I call the working side of the utility; it is there you either get information you are looking for or perform tasks on the selected drives or partitions. The tasks you are allowed to do are controlled by the tabs at the top of the window: Information, First Aid, Erase, Partition, and RAID. We’ll step through each one.

The Information Tab

The Information tab simply displays relevant information about the selected drive or partition. Clicking on a drive icon displays relevant information about its hardware set up.

Selecting a partition displays information about how the partition is set up:

Here you can see the mount point (“/” tells you it is at the root of the drive), the format used on the partition (HFS+ = HFS Extended), the size of the partition (41.66 GB), space available (26.52GB), space used (15.14GB), and the number of files (223,315) and folders (48,374) on the disk.

If you use this information along with the drive info, you can tell that the boot disk is a Western Digital 120GB hard drive I have partitioned twice. One partition is named Jaguar and one Panther, in honor of the Mac operating systems installed on them. I made the Jaguar partition 45GB and left the rest for Panther.

You may think there is a discrepancy between the size of the hard disk displayed in GB and the number of bytes shown. There really isn’t; the difference is due to the definition of a gigabyte which is 1,073,741,824 bytes or 1024 megabytes. (A kilobyte is 1024 bytes. A megabyte is 1,048,576 bytes or 1024 kilobytes. And it’s all because computers use a binary (base 2) number system.)

NOTE: Of course, a computer’s BIOS-- or Open Firmware in the case of a Mac-- uses some hard drive capacity to store information it needs to run and manage the hard disk. That’s part of the reason why the hardware always reports something less than what the hard drive’s marketing description led you to believe what was in there. The other part is because of the difference between bytes and bits and a marketer’s desire to state the biggest number they legally can. So, my 120GB hard disk only shows 111.79GB available. There’s lots of discussion on the web about this subject if you want to understand more. I consider the loss just a fact of life and use the hard disk’s marketed size as a “relative” measure rather than an exact one.

Once you have the information you’re looking for, it’s time to move on to actually doing something to repair your disk or make the operating system run correctly, which is probably why you’ve called up Disk Utility in the first place. Let’s look at the next tab in the utility, i.e., First Aid.

Click here to continue.