Factory restore Mac?

what will happen if i just factory restore with out erasing first the HDD?

Then it wouldn't be a 'factory restore'... if you elect to only install the OS, all of the information on your disk will be retained.

If you want a 'true' 'factory restore' see Thomas Reed's article, How to prepare your Mac for sale.

Clinton

If you planning to sell or give away the computer, then you need to properly erase the drive to prevent your information from being accessed by other people.

If you just need to restore OS X in place, then you don't need to erase the drive first.

Erasing the drive and reinstalling is the only way to reset to "factory default" state.

What is it you want to accomplish?

Reinstalling Lion/Mountain Lion In Place Without Erasing the Drive

Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.

When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the main menu.

Reinstall Lion/Mountain Lion: Select Reinstall Lion/Mountain Lion and click on the Continue button.

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

Install or Reinstall Lion/Mountain Lion from Scratch (Erase and Install)

Be sure you backup your files to an external drive or second internal drive because the following procedure will remove everything from the hard drive.

Boot to the Recovery HD:

Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.

Erase the hard drive:

1. Select Disk Utility from the main menu and click on the Continue button.

2. After DU loads select your startup volume (usually Macintosh HD) from the

left side list. Click on the Erase tab in the DU main window.

3. Set the format type to Mac OS Extended (Journaled.) Optionally, click on

the Security button and set the ZeroData option to one-pass. Click on

the Erase button and wait until the process has completed.

4. Quit DU and return to the main menu.

Reinstall Lion/Mountain Lion: Select Reinstall Lion/Mountain Lion and click on the Install button.

Note: You will need an active Internet connection. I suggest using Ethernet if possible

because it is three times faster than wireless.

Follow these instructions step by step to prepare a Mac for sale:

Step One - Back up your data:

A. If you have any Virtual PCs shut them down. They cannot be in their "fast saved" state. They must be shut down from inside Windows.

B. Clone to an external drive using using Carbon Copy Cloner.

1. Open Carbon Copy Cloner.

2. Select the Source volume from the Select a source drop down menu on the left side.

3. Select the Destination volume from the Select a destination drop down menu on the right

side.

4. Click on the Clone button. If you are prompted about creating a clone of the Recovery HD be

sure to opt for that.

Destination means a freshly erased external backup drive. Source means the internal

startup drive.

Step Two - Prepare the machine for the new buyer:

1. De-authorize the computer in iTunes! De-authorize both iTunes and Audible accounts.

2, Remove any Open Firmware passwords or Firmware passwords.

3. Turn the brightness full up and volume nearly so.

4. Turn off File Vault, if enabled.

5. Disable iCloud, if enabled: See.What to do with iCloud before selling your computer

Step Three - Install a fresh OS:

A. Snow Leopard and earlier versions of OS X

1. Insert the original OS X install CD/DVD that came with your computer.

2. Restart the computer while holding down the C key to boot from the CD/DVD.

3. Select Disk Utility from the Utilities menu; repartition and reformat the internal hard drive.

Optionally, click on the Security button and set the Zero Data option to one-pass.

4. Install OS X.

5. Upon completion DO NOT restart the computer.

6. Shutdown the computer.

B. Lion and Mountain Lion (if pre-installed on the computer at purchase*)

Note: You will need an active Internet connection. I suggest using Ethernet if possible because

it is three times faster than wireless.

1. Restart the computer while holding down the COMMAND and R keys until the Mac OS X

Utilities window appears.

2. Select Disk Utility from the Mac OS X Utilities window and click on the Continue button.

3. After DU loads select your startup volume (usually Macintosh HD) from the left side list. Click

on the Erase tab in the DU main window.

4. Set the format type to Mac OS Extended (Journaled.) Optionally, click on the Security button

and set the Zero Data option to one-pass.

5. Click on the Erase button and wait until the process has completed.

6. Quit DU and return to the Mac OS X Utilities window.

7. Select Reinstall Lion/Mountain Lion and click on the Install button.

8. Upon completion shutdown the computer.

*If your computer came with Lion or Mountain Lion pre-installed then you are entitled to transfer your license once. If you purchased Lion or Mountain Lion from the App Store then you cannot transfer your license to another party. In the case of the latter you should install the original version of OS X that came with your computer. You need to repartition the hard drive as well as reformat it; this will assure that the Recovery HD partition is removed. See Step Three above. You may verify these requirements by reviewing your OS X Software License.