This how-to shows you the steps using Disk Utility 13 in OS X 10.10 Yosemite, but the process is the same if you’re using OS X 10.9 Mavericks or 10.8 Mountain Lion. Sometimes you want to wipe out all the data that’s on a hard drive or solid-state drive—erase it and start over. The best way to do this is to format the drive, which both erases the drive and prepares it for storing data by mapping out bad sectors, creating address tables for locating the data on the disk, and more. Similarly, you may have purchased a new drive that was formatted for Windows out of the box. You'll want to reformat that drive for your Mac. But formatting a drive so that it can be used as your Mac’s startup drive requires a slightly different procedure than formatting it for use as a secondary drive for storing data. Click the Erase tab if it’s not already selected.
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To format a hard drive means to delete any information on the drive and to set up a file system so your operating system can read data from, and write data to, the drive. As complicated as that might sound, it's not really difficult to format a hard drive in any version of Windows. Why Need to Format External Hard Drive for Mac and PC. To put it simply, if you want to share external hard drive between Mac and PC, you need to format an external hard drive for Mac and PC. Currently, hard drives for Windows PC are always formatted with NTFS, while hard disks for Mac are formatted with HFS+.
At the bottom of the window, you’ll see some information about the drive you have selected. Look at the Partition Map Scheme entry. If it says GUID Partition Table, you can format the drive by selecting Mac OS X Extended (Journaled) in the Format pop-up menu, giving the drive a name, and then clicking Erase. (Remember: This erases everything on the drive!) You can now skip directly to Step 8. If the Partition Map Scheme says Master Boot Record or Apple Partition Map, you need to continue to step 5.