How do I format a USB stick on my iMac

Drive Preparation

1. Open Disk Utility in your Utilities folder.

2. After DU loads select your hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.

3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to GUID then click on the OK button. Set the format type to Mac OS Extended (Journaled.) Click on the Partition button and wait until the process has completed.

4. Select the volume you just created (this is the sub-entry under the drive entry) from the left side list. Click on the Erase tab in the DU main window.

5. Set the format type to Mac OS Extended (Journaled.) Click on the Security button, check the button for Zero Data and click on OK to return to the Erase window.

6. Click on the Erase button. The format process can take up to several hours depending upon the drive size.

Steps 4-6 are optional but should be used on a drive that has never been formatted before, if the format type is not Mac OS Extended, if the partition scheme has been changed, or if a different operating system (not OS X) has been installed on the drive.

To format a partition, you have to use Disk Utility. Follow these steps:

1. Open Disk Utility (it's in Utilities folder, inside Applications folder) and choose your USB drive on the sidebar.

2. Go to Erase tab, choose the format you want next to "Format", and then, press Erase button. Your USB drive will be formatted.

If you need graphic help, see > http://pondini.org/OSX/DU1.html

Note that GUID partition table is completely optional, and if you have to use your USB drive with a PC, I recommend you to not modify it because you may have problems when you connect it to PCs

On Mac, that's not possible,

What format do you want to use with the USB drive? If you want to use exFAT (it's the best if you want to use your USB drive with Macs and PCs), you must erase the USB drive on your PC with Windows. That's because OS X, when it erases the disk with exFAT, makes your USB drive unreadable for PCs. This doesn't happen if you format your USB drive using FAT32 (it shows in Disk Utility as "MS-DOS (FAT)")

There is only one universal format, FAT32 or MSDOS. If the flash drive is formatted as such already then you need do nothing to use it on a Mac. If it's formatted NTFS, then:

Drive Preparation

1. Open Disk Utility in your Utilities folder.

2. After DU loads select your hard drive (this is the entry with the mfgr.'s ID and size) from the left side list. Click on the Partition tab in the DU main window.

3. Under the Volume Scheme heading set the number of partitions from the drop down menu to one. Click on the Options button, set the partition scheme to MBR then click on the OK button. Set the format type to MSDOS. Click on the Partition button and wait until the process has completed.

I forgot to say that exFAT is only compatible with Windows XP SP3, Vista, 7 and 8, and the main advantage respecting to FAT32 is that you can store files bigger than 4 GB on your USB drive. That's why I recommend it

dadlewis wrote:

This is a simple 4GB usb formated on a MS PC and I just want to reformat it in universial format.

It's likley already formatted FAT32 by default and will work on a Mac or PC just fine.

Since it's only 4GB you can't put larger than 4GB sized files on it, so there is no need to format it exFAT on a PC or OS X Extended Journaled on a Mac for larger than 4GB sized files.

Just use it like it is FAT32/MSDOS and if it's NTFS, then use Disk Utility to format it: Partition 1, Option: MBR, Format: MSDOS.

Drives, partitions, formatting w/Mac's + PC's

I have the same question. All the replies were helpful but when I tried to follow directions I received this error message: "couldn't unmount disk" What does this mean, please? Unsure how to proceed.

Thanks,

Tara

I too had the same problem. On a PC, you simply right click and select "format." The reason I wanted to do this on the mac is because I have an 8gb usb flash drive that for some strange reason, when I deleted all the files it still showed only 1.5 gb available making it impossible to put any more than 1.5 gigs of new data on it.

I went to utilities like the previous posters said and simply clicked "erase." No need to partition, don't understand why you would need to do all of that to do a simple format. I too, got the "couldn't unmount disk" message so I went to the drive on the left, right clicked and clicked "unmount disk" then went ahead and erased it. Now it's good as new.

This is the first convoluted thing on mac that I have come across as compared to windows. I have been a mac user for 2 years now and swear by them but this is probably one of the dumbest things I have seen yet. At least now I know how to erase. Way too complicated but everything else on a mac is way better than windows.

I hope this helps.

Thank you - you have solved my problem. Thanks so much for answering!

hey please help me i have the same problem but i can't press the erase button!