How to format a thumb drive, hard disk or SSD drive.


You may not know that USB Thumbdrives come in different formats. This article explains why this matters and how to format a USB drive into the format that you want.


Formatting a Thumb Drive or Hard Disk.

1. Open Disk Utility. (It is in the ‘Utilities’ folder in the  ‘Applications’ Folder on your computer.)

2. Insert tahe thumb drive and it will appear in the left window pane like this:

disk util

3. Select the Thumbdrive. (Here it is called ‘16.01 GB TOSHIBA). Some options will appear in the main window. Click on the ‘Erase’ Tab as follows:


If you now click on ‘Format’ you will see a list of the available formats. You will need to select the format that you want. Here is a little bit about each one.

Mac OS Extended is the standard Macintosh Format that has been in use since OS-X Panther 10.3

Journaled is safer – it adds some protection to make the thumb drive data safe if the power cuts out or the drive is pulled out when it is still in use.

Case Sensitive just means that upper case and lower case filenames are treated differently.

Encrypted means the data is password protected.

For best performance you should select ‘Mac OS Extended (Case-sensitive, Journaled). This is the fastest and safest system. It will work with versions of OS-X  since to 10.3 (Panther).

You can select ‘Encrypted’ if you want the drive password protected. It will ask you for a password. If you forget the password, all the data on the disk is lost forever!

MS-DOS (FAT) is for PC computers (and other devices like TV’s and cars). They cannot read Mac OS Extended format. MS-DOS (FAT)  allows the USB drive to be read on a PC computer. Most thumb drives you purchase come formatted as MS-DOS (FAT) by default. Macintosh computers can read PC formatted thumb drives but PCs cannot read Macintosh formatted thumb drives. Also, MS-DOS formatted drives cannot handle files over 4GB.


Mac OS Extended (Case-sensitive, Journaled): Fastest and best.

MS-DOS (FAT): Compatible with non-macintosh computers, but 4GB file size limit.

Mac OS Extended (Case-sensitive, Journaled, Encryoted): Secure but don’t lose the password!

Once you’ve selected the format you want just select ‘ERASE’ and it will take about 20 seconds or so to erase the drive depending on it’s size.

All this information is true for USB Hard Drives and SSD drives as well.

Creating a Boot Drive.

You don’t need to read the rest of this article unless you want to make a ‘Boot Drive.’ If you want to put a copy of OS-X on the drive and boot off it, then there is one more step you need to add to the above. You need to go to the ‘Partition’ tab, it will look like this:

partition tab

Select ‘1 Partition’ as in the picture above, and then press the ‘Options’ button. You will be prompted to choose a partition scheme.


Notice that each partition scheme allows you to boot a different computer. ‘GUID’ is for current day Macintosh Computers. Older PowerPC based macs (prior to 2006 – the G3. G4 G5 etc) need the ‘Apple Partition Map’ and PC Windows Computers need the ‘Master Boot Record’.

You will probably never need to use the bottom two. If you but a Hard Drive or Thumb Drive from anyone other than Apple, it will probably come formatted as ‘Master Boot Record’ and so you will need tot change the partition to ‘GUID Partition Table’ if you want to be able to Boot from it.


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