How To Format External HDD / USB Flash Drive on Mac Easily

You can format a hard drive or USB flash disk specifically so that it will be compatible with both Mac OS X and Windows PC computers. Though this excellent cross-platform compatible ability is unknown to many users, it's not a complex process, and if you frequently use both a Mac and Windows PC you will find this particularly useful because any data, media, or files stored on the the drive will always be accessible from any operating system. It only takes a few minutes to start, and it's extremely easy, and we'll walk you through the entire process in a few simple steps. This is a simple procedure and is achieved the same way for all drive types and through all connections, be they USB, Firewire, or Thunderbolt. Formatting a drive will erase all data and partitions on the disk:
  1. First you need to connect the hard drive or USB key to the Mac.
  2. Now launch the Disk Utility, which is located in Applications section, and then go to Utilities. Disk Utility Wizard
  3. You need to locate the drive name from the left-hand side of Disk Utility and click on it.
  4. Click on the “Erase” tab across the top. Select the Disk to Format
  5. Click the "Format" drop-down menu and select your preferred file system. Optionally, enter a name for the drive in the "Name" field.
  6. Click "Erase" button, and a prompt will pop up, which will ask again to click or Erase button, if you are not sure, then go with the Cancel button. Click On Erase Button Once Again
That's all there is to it, the drive will now format. Note: After formatting, the existing data will be gone. Make sure to back up any important data before formatting the drive. Smaller external hard drives, SSD's, and USB flash keys format quickly, while a larger hard drive may take a while longer. After completion the drive will be formatted to the Mac OS X compatible HFS+ file system