Most off-the-shelf USB flash drives are formatted for Windows computers. You can easily reformat a drive to use the standard Mac OS Extended format with the Disk Utility app. Keeping the drive in MS-DOS format may be a better option, however, if you plan to use it on both Mac and Windows computers.

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Video Transcript: So let's say you get a little USB drive andyou want to use it with your Mac. When you plug it in you may find that it'snot formatted for Mac, it's formatted for Windows of course because most computers outthere are Windows machines. But you want to format it for a Mac. It's easy to do. You just have to use the Disk Utility appthat you already have on your Mac. Now I've inserted the drive into my Mac intothe USB port. I'm going to run Disk Utility here and itwill come up as one of the drives on the left. There it is. It's the 16 GB external physical disk drivethere I can see it's got one partition on it called No Name. And sure enough it's an MS-DOS partition. So what I want to do is I want to reformatthis whole drive as a Mac drive. So I don't want to select just the volume,just that one partition. I want to select the entire thing and I wantto hit Erase. I'll give it a better name. Maybe I'll use my name there so it can identifiedit if I loose it in a computer lab or in school or something. I'll choose a format. I want Mac OS Extended Journaled. That 's your standard Mac format. Now I get to pick a scheme. So this is kind of a level of formatting thedrive here. What I want to choose is either Master BookRecord or GUID Partition Map. GUID is standard for Macs now so that's whatI'll choose right here. Then I'll hit erase and it'll erase the driveand create this one volume, this one partition on it called My Drive. Then I'll be able to use it on my Macs. Now I should note that MS-DOS isn't that badof a format especially if you want to use this drive between both Mac and Windows machines. Because your Mac can understand MS-DOS formatjust fine but Windows won't be able to understand Mac. So only format the drive as Mac Only if you'reonly going to use it on your Macs. So you can see here it's done. I've got My Drive and it's now formatted MacOS Extended.