MacMost Now 321: Using Disk Utility to Format Drives

Learn how to use Disk Utility to erase and format an external drive. You can also create drives with multiple partitions.
Video Transcript / Captions
Closed captioning for this video is available on YouTube: MacMost Now 321: Using Disk Utility to Format Drives.

Hi. This is Gary with MacMost Now. Today's episode let's learn how to format a hard disk using disk utility. So disc utility is the go-to application for Mac experts to format hard disks. Let's go and take a look at how it works. Disc utility is located inside your utilities folder inside your applications folder. When you run it, it immediately gets to work and looks for all the drives that are connected to your machine. You'll even see optical drives. In this case I've got the Macintosh hard drive, which is the internal drive for this iMac. I've also got a 250 gig external hard drive hooked up and on it is one volume.
So a disk is a physical drive, like this one. A volume is a space on that drive that shows up as a hard disk on your machine. Typically, you would have one volume on a hard disk but you can actually partition it into two or more volumes on a hard disk. So here in disk utility if we wanted to reformat this drive, we would select the drive not necessarily the volume. Then we can click erase and on there we get some options. We usually want to choose the latest version of the Mac format, which is Mac OS extended journaled. But we can also choose an older drive in case we need to hook this one up to older machines. We can also choose to do it as a Microsoft compatible drive, which the Mac can read but can also be read by Windows machines.
Once we've chosen that we can choose a name and then we can click erase. This will reformat the drive and create a new volume on that drive replacing any old volumes that were there. One reason you may want to use disk utility to format a new drive that you get is a new drive may be formatted for Windows and you may want to reformat it specifically to use for a Mac. You can use it either way but it'll be more efficient if you actually formatted OS 10 extended.
So here we go. Now we've got this volume test on our external hard drive. We can also do some other things. For instance, if we wanted to create multiple volumes we could partition the drives. So instead of erase, click partition and here it tells us there's one - a large partition - and it's called test. We could change this to be say two partitions and we get to name each one of these and also change its size by changing the number in here or simply dragging the divider around. If we do that, we end up with two partitions and two volumes on that single drive. They would both show up whenever we connected this external drive to our Mac.
Now multiple partitions aren't always very useful, but you can use them for organizational purposes. You can also use them to create a single partition that holds scratch files. These are files used by video editing software and photo editing software that sometimes takes a lot of disk space but it's not something you really ever have to back up cause you can specify a time for the machine to only back up a certain volume and ignore another one.
Also, of course, this is very convenient way to erase an entire drive. You can drag everything to the trash and throw it away. But it's still going to leave a lot of junk behind and it may take some time to empty the trash if you have a ton of files. Just simply reformatting the drive would only take seconds. This technique also works for the little, tiny USB flash drives and I use it all the time to simply reformat them and start over using them for a new purpose.
So I hope you found this look at disk utility useful. Till next time, this is Gary Rosenzweig with MacMost Now.

Comments: 8 Responses to “MacMost Now 321: Using Disk Utility to Format Drives”

    9 years ago

    Thanks Gary!
    About partitioning volumes (not formatting), there’s a less known feature available since Leopard I think. It is the ability to change the size of existing partitions and this action, if you stay on free space, won’t erase the existing data if any. This could be very handy.

      9 years ago

      Yes, you can do that if the drive is formatted properly, and if the drive supports it — not all drives support it. So I recommend a complete backup of all data on the drive before attempting this.

    edward McCrea
    9 years ago

    Hi Gary
    I have started looking at macmost and find it useful enough to keep on your mailing list as well as recommend it to other folk as well. So thanks for you time. I found the disc utility very useful and one of those things that I often forget how to do because you do not use it all the time and when you need it you know it is there but can never find it. So thanks for this post. I have now made notes and stored it somewhere I can find it. I am a pc user that just recently switched to mac (very happy I did) but I still find somethings hard to do on a mac because I am stuck in pc mode. . . learning fast.

    Something I am looking for is information on how to use time machine – again not something I use a lot but I am pretty clueless about how to use it and if you can recommend any resources that would be much appreciated.

    Teddy McCrea

    9 years ago

    Your book is OK,but Iam not a computer person.Your videos at Mc Most are To fast.So why dont you make DVDs of each chapter of your book slow down your examples and speech.Put the DVDS on sale to the public,I know that I would buy them. Thank you for showing me a lot.A person who has never used a computer before,but would like to learn. Thanks Gill Jacobson

      9 years ago

      The DVD model hasn’t really worked for the most part. You have to sell too many of them to make it worth it — only a few companies have been able to do it, and with a lot of marketing effort. I think the book is a good alternative for many, but I know I can’t please everyone.

    9 years ago

    Lary, keep doing the great job! I am not a Mac person. A friend gave me a Powerbook G4. I want to erase all the data completely and have it clean to sell it. (I believe somebody could use this cute, but with lots of scratches, laptop.) The friend doesn’t have the installation CD. Question: Can I somehow do what I want without it? (I think I can’t format the drive where operating system is installed.) Thanks.

      9 years ago

      You need to installation CDs to do that. Alternatively, you could do it with a Mac OS X (10.3, 10.4 or 10.5) install CD too, though it wouldn’t replace the iLife applications, only the base OS and base applications.
      So you might be better off selling it to a used Mac shop that can re-install the system on their own. See if there is one in your area.

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