deleting a partition on a hard drive

You have a used computer that someone delivered without wiping the drive and installing the original software. If this model is from 2011 or later, then do the following. If it is from 2011, then first check this out: Computers that can be upgraded to use OS X Internet Recovery.

Install OS X Using Network Recovery

Boot to the Network Recovery Server:

Restart the computer and after the chime press and hold down the COMMAND-OPTION- R keys until a globe appears on the screen. Wait patiently - 15-20 minutes - until the Recovery main menu appears.

Partition and Format the hard drive:

1. Select Disk Utility from the main menu and click on the Continue button.
2. After DU loads select your newly installed hard drive (this is the out-dented 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 Apply button and wait until the process has completed. Quit DU and return to the main menu.

Reinstall OS X: Select Reinstall OS X and click on the Continue button. Be sure to select the correct drive to use if you have more than one.

Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.

This should restore the version of OS X originally pre-installed on the computer.

I the iMac is pre-2011, then do this instead:

Clean Install of Snow Leopard

1. Boot the computer using the Snow Leopard Installer Disc or the Disc 1 that came

with your computer. Insert the disc into the optical drive and restart the computer.

After the chime press and hold down the "C" key. Release the key when you see

a small spinning gear appear below the dark gray Apple logo.

2. After the installer loads select your language and click on the Continue

button. When the menu bar appears select Disk Utility from the Utilities menu.

After DU loads select the hard drive entry from the left side list (mfgr.'s ID and drive

size.) Click on the Partition tab in the DU main window. Set the number of

partitions to one (1) from the Partitions drop down menu, click on Options button

and select GUID, click on OK, then set the format type to MacOS Extended

(Journaled, if supported), then click on the Apply button.

3. When the formatting has completed quit DU and return to the installer. Proceed

with the OS X installation and follow the directions included with the installer.

4. When the installation has completed your computer will Restart into the Setup

Assistant. After you finish Setup Assistant will complete the installation after which

you will be running a fresh install of OS X. You can now begin the update process

by opening Software Update and installing all recommended updates to bring your

installation current.

Download and install Mac OS X 10.6.8 Update Combo v1.1.

You have a Recovery HD from which to boot the computer to perform such activities:

Boot to the Recovery HD::

1. Restart the computer.

2. Immediately after the chime press and hold down the

"COMMAND" and the "R" keys together.

3. Release the keys when the Utilities Menu appears.

If this is a new, out of the box computer, then what leads you to believe there are two partitions on the drive? You cannot reformat a drive without erasing everything on the drive. That includes the OS. However, one must completely re-partition and reformat the drive back to case insensitive. There is no other way to do it. And, it cannot be done from the Recovery HD. You need to use Network Recovery such as outlined above or, if the computer came with Snow Leopard originally, by booting from the Snow Leopard DVD as shown above.