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Hi, this is Gary with MacMost.com. Let me show you how you should format an external drive for your Mac. 

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Now when you buy an external drive, whether it is a large hard drive like this or just maybe a small USB thumb drive, you need to format it for your Mac. Even if when you buy the drive it says that it is formatted for Mac, it maybe using an older format and most of the time when you buy drives they are actually formatted for Windows. 

So when you connect a drive it should appear here on the left side of the Finder under locations. Here's this drive. It's not a new drive but I'm going to use it for this demonstration. If I select it it shows what is in there and chances are if it is a brand new drive that you bought it should mount just fine and show there is no files in there or maybe some junk in there like some software that was included with the drive. It is probably for Windows, not for Mac. 

Now to see the format of the drive you can select it here and then go to File, Get Info. Then you'll see information about the drive including Format. Now you can see here this is formatted for modern Macs using APFS. But chances are you're going to see something else there. Now keep in mind formatting a drive means erasing it. So if this isn't a new drive, but something you've had for awhile and you want to format it correctly now, the first thing you want to do is get all the data off of it. Put it on another drive, move it to your internal drive, make sure there is nothing you need on the drive because you're going to erase it and all those files are going to be gone when you format the drive. 

So to format the drive you need to run Disk Utility, which is an app that comes with your Mac. I'm going to use Launchpad to search for and run Disk Utility. Now what you should see here are internal and external drives including the one you have attached. I like to make sure that in View I have Show All Devices so I see exactly what's going on here. Otherwise you're actually seeing the volumes on the drive, not the drive itself. Since we want to reformat the whole drive we want to make sure we can select the whole drive and there's no confusion. So by doing this you can see how it opens up everything here. You can close things and open things like that. But the top level is going to be the physical drive itself, not the containers and volumes inside. So in this case I can locate the drive by its name here. Maybe yours is Untitled or blank or something like that. Then I can select the actual drive itself just above it. 

Now to reformat it what I need to do is click the Erase button at the top. This is where you have some choices to make. So, first of course you get to name the drive. So name it something appropriate. It's easy enough to change it later on but it is good to start off with the right name. Then you need to choose a format. So if you click here you get a lot of different options. So at this point the question is do you want to use the drive just for your Mac or is this drive going to be used to go between computers, specifically between Mac computers and Windows computers. Now it should be rare today that you actually want to use an external drive to go between Mac and Windows' computers. This used to be really common when we had very limited files sharing options. But today with Cloud Services like iCloud, DropBox, One Drive, etc., it is much easier to use those Cloud Services to see the same files on different devices rather than actually having to disconnect the drive and reconnect it to another computer and back and forth all the time. So today external drives more likely are just going to be attached to your Mac or attached to your Mac when you need to access the files on them and not something that goes back and forth.

In that case you want to use a Mac format. APFS is the modern Mac format. You can use the older Mac OS Extended format but it is really not necessary unless you still have very old Macs where you want to use this drive there as well. For most uses APFS is what you want to do today. Now there are case sensitive versions here. You don't need to worry about using that. For regular use just plain APFS works. Encrypted is a way to have a password set on the drive. The actual contents of the drive are encrypted. You can't get to the contents without the password. This means when you plug it into your Mac it will prompt you for a password. The same if you reboot. It's not as inconvenient as it sounds because you can actually save that password in your Keychain so when you connect and reconnect the drive to your Mac you shouldn't have to do anything. Which is actually kind of a danger because you can go months or years forgetting that there's a password for the drive and then connect it to a different Mac and then it prompts you for a password and you can't remember what that is. So if you do decide to use encrypted make sure you've got that password saved in your Password Manager or written down somewhere and remember that the drive is encrypted like that. 

But either way APFS or APFS Encrypted are probably the best things to use if you're just using your drive on a Mac. However, if you do need to use this drive on Windows then the choice is clear. You need to use ExFAT. Regular FAT is a very old format that has extreme limitations. It may work fine for little USB thumb drives like this. But you're going to want use ExFAT and it will work on any modern Window's system. 

Now there's also something called  Scheme here and you get to choose between GUID Partition Map, Master Boot Record, or Apple Partition Map. These two are older Schemes and for the most part you don't need to worry about them today unless you've got very old machines where you want to use this drive. For a long time GUID has been the Scheme that you want to choose. 

So once you have this all setup you click Erase. It will reformat the drive again erasing everything that is on there. Now it is a blank drive and ready to use. Now keep in mind if you want to use this external drive for Time Machine then you really don't need to worry about any of this. Time Machine is going to make sure it is formatted correctly. So you could have just plugged the drive in and you may have even gotten a prompt asking if you wanted to use this drive for Time Machine. Then you could just go through the instructions there to set it up. Otherwise if you go into System Settings and then General and then Time Machine you can add a Time Machine drive like this, select that drive, click Setup Disk, and it will give you some options here. When you hit Done it will actually reformat that drive to exactly what Time Machine wants. So it is not necessary to format the drive first in Disk Utility and then go through this process. This process would take care of formatting the drive all by itself. 

Hope you found this useful. Thanks for watchi ng.