Cannot read a bootable disk? cannot format? how to repair it?

Formatting your new external hard drive is not as difficult as you may think. In fact, you don't even have to be a computer techie or uber-Mac geek to perform this procedure successfully.

The tool you would use, to format your drive within your Mac OS X system, is the built-in utility application called Disk Utility.

Disk Utility is Apple Inc.'s defacto utility application, for performing disk related tasks within the Mac OS X volume.



From creating new images, to burning CDs and DVDs to formatting hard drives, Disk Utility performs well enough to keep not only your Mac OS X volume on your hard drive error free, but keep your hard drive healthy and error-free as well.

I could go on in detail, admirably describing more features of this versatile Mac OS X tool, but the purpose of this FixYa tip, is to show you how to easily format your external hard drive. So that is where I will take you now.
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There are generally two formats in Disk Utility that you can use to effectively format your hard drive.

Mac OS Extended (Journaled) - if you want a Mac readable hard drive only

MS-DOS (FAT 32) - If you want your external hard drive to be read by both Mac and PC.

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--STEPS FOR FORMATTING YOUR HARD DRIVE WITH DISK UTILITY--
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• First, make sure your external hard drive is connected securely to your Mac and is turned on.

•Next, from your desktop, click anywhere on a blank space on your desktop. Now you should see Finder listed near the Apple menu icon.

• From the Finder menu, click on Go, then Utilities from the
drop-down menu. This will take you to your Utilities* folder.

(*You can also get to the Disk Utility application via Applications > Utilities folder)

• Now, locate and launch the Disk Utility application.

When Disk Utility opens you will see a left side window, which will show
all connected hard drives and optical drives. It is here that you
should see your external hard drive listed in that window.





• When you locate it, simply select it and then select Partition
from the tabs on the right hand side.



• Change the Volume Scheme from Current to 1 Partition

• Make sure to provide a name for your new external hard drive.

• Select Mac OS Extended (Journaled) from the Format
drop down menu, for a bootable Mac only external hard drive.

• Or select MS-DOS from the Format drop down menu, for a bootable Mac & PC external hard drive.

From there, click the Options button, located toward the bottom of
your window.


This will open a partition scheme selection window as seen in this screen shot:




• Select GUID Partition Table for bootability on a Intel processor based
Mac.

• Or select the Apple Partition Map for bootability on a PowerPC based Mac.

• Click the OK button.

Finally, click the Partition button and allow Disk Utility to format your new external hard drive.

When this process is complete, you now have a newly formatted, ready to use hard drive.

Believe it or not, this process can be completed faster than you think.
Using this method with Disk Utility, I was able to format my new 1TB Iomega USB external in less than 20 minutes.
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Final Note:
I used the external hard drive as the focus for showing you how to format and prepare your hard drive for use on your Mac, but this feature can also work with internal hard drives as well.
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For more information about some of the disk repairing features of Disk Utility, here is a great support link for this nifty and quite effective Apple utility for the Mac OS X platforms:

Using Disk Utility to repair a disk

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Thanks for reviewing my Mac OS X Tip!

Regards,

-Mactechtrainer

When you are getting the disk read error and when you try to get it ok by bootable cd at that time you find that the drive is showing the unknown format.

In this case simple remove you faulty hard drive and plug into the another system where the operating system is same and format is also same eg. ntfs or fat32.

keep the HDD as secondary and start the system and go to manage-->disk management and click on the damage partition and it will try to recover it automatically and after that you get the unkown to ntfs than restart and chekc the hdd.

you can take backup of your c drive and than replug the hdd to your original system and most probaly it will start properly

And if do not do so than you can repair by bootable ok

In this way you can recover data from the unknown partition also.