Accidentally deleted startup disc

Startup again in Recovery mode (command + R) or if that doesn't work try forcing Internet Recovery Mode with command + option + R. Once the startup process is complete & you see the OS X Utilities screen, choose Disk Utility.

Once that is running, select your internal hard drive from the list on the left (not the volume name indented below it). If you have chosen the drive (which typically has a name suggesting its capacity) you will see a "Partition" tab in the Disk Utility window. Click it. From the popup choices for "Partition Layout" choose 1 partition. Make sure the "Format" choice shown is "Mac OS X Extended (Journaled)." Click the Apply button & confirm that you want to repartition the drive.

Wait for the process to complete. If it does without displaying any errors, quit Disk Utility & now try selecting Install (or Reinstall) OS X from the OS X Utilities menu.

If you get any error while doing the above, report at what step it occurs & what the error is.

PLEASE let me know if you resolved this issue. I am having the exact same problem as you've described it and at a loss for what to do. Was trying to restore to factory settings as I bought the computer from a friend, don't have AppleCare on it or anything

If you do not have a backup, there is no way to reverse the erase. If you did not use one of the secure erase options, you may be able to get some or all of your data back by using file recovery software like Data Rescue 3, otherwise there is no hope of getting it back.

Note that if you want to try to recover your date, you must not do anything that will write anything to the drive, including reinstalling the OS. That means you can't start up from it or restore any of the files back to it until the process is complete, so you will need an external drive to copy the recovered files to, & possibly an external DVD reader to run the recovery software from.

When I am pressing command key and the r key ..its directly get me the internet recovery mode even I didn't touch the option key ,so I am not getting the utility menu before internet recovery . Becoz I have several partition in my mac ..I want to install Mac os in a specific partition without harming another partition .. If I do internet recovery ,is it erase all of my hard-disk ...it's really important for me to save my data ,which is saved already in another partition in dis hardisk . ...pls help

Thanks so much for this... worked for me and I thought my laptop was done for. Thank you!!

Jennseay0393 wrote:

Ok, this now seems to be a lot more complicated than originally anticipated

So after startimg internet recovery, and selecting install mac os x i still have no operating system.

I get a message on the screen saying "could not write installation information to disk. Contact AppleCare."

What does this mean? How can I get my Mac Os back? Help!!

Boot while holding the option key.

You should see Recovery HD.

Select it and try Reinstall OS X again

Since you "erased the entire thing", threre is nothing to recover (with OS X Recovery Mode).

Where are you seeing Mac OS X base system?

I thought that the options were:

• Restore from Time Machine Backup
• Reinstall OS X
• Get Online Help
• Disk Utility

http://www.prosofteng.com/products/data_rescue.php

http://www.prosofteng.com/downloads/ $99 (might be cheaper on Amazon)

You can demo to see if it will work before you buy.

http://www.prosofteng.com/docs/Data-Rescue-3-Users-Guide/pages/intro.htm#intro_d emo

You said you backed up some data to iCloud.

Also Apps purchased from AppleStore can be re-downloaded and most other Vendors have ways to re-install Apps.

OS X can be re-installed.

So, the question is, how much data is there that you did not back up to iCoud (i.e. pictures, music, worksheets, etc), this is what you want to try to recover with Data Rescue.

Also, as you have a MacBook Air, and no system installed, by installing OS X you will write over data you are trying to recover, so you should install OS X and Data Recovery to a USB stick (you'll need a 16GB stick, $20)

Prosoft (makers od Data Rescue) have instructions on how to do this here:

http://www.prosofteng.com/support/datarescue3-bootable-usb.php

Other Data Rescue guides: http://www.prosofteng.com/support/datarescue3.php

It's been awhile since I did this, but I think all you need to do for a bootable USB with ML is to Boot into Recovery on you MacBook Air, Format the USB as GUID, then when you select Intall OS X, choose the USB to install to (this will take awhile). Then once installed, reboot your Mac while holding the option key, and select the USB drive with OSX. Then use Safari to go to the Data Recovery Website and install Data Recovery to the USB

Jennseay0393 wrote:

Oh no! There's no other disc or place that keeps files and stuff?

So when I restart computer I go directly to Safari and Data Rescue 3 and download?

The only place that keeps backups is iCloud, Time Machine, etc. If you have not been making backups there is no other place it is stored besides on the drive you erased. That's why it is so very important to regularly make backups!

Also, just to be sure you understand, you cannot write anything to the drive until you have attempted to recover data from it. That means you cannot install the OS & Safari on it. That means you can't start up from it (because you erased the OS that runs the machine), or reinstall the OS from the Recovery partition, or in any way involve that drive besides reading data from it with a utility like Data Rescue 3.

You will need to purchase Data Recovery 3, a suitable external drive for the recovered files, & something like a USB stick to install the OS on, like Tony T1 suggested. I suggest getting an external drive twice or larger than the capacity of your built-in drive so you can use it later for Time Machine backups.

If, after reading all the Prosoft instructions, you still have questions, you can contact the company's product support -- after all, you are paying for the product so you might as well get your money's worth.

Jennseay0393 wrote:

I think I did start back up my computer from the same disk, I will have to check. So the chances of there being any data on there is slim anyway. ?

If you mean the internal disk in your MBA, you could not have started up from it after it was erased (except possibly in Recovery mode.)

In case it isn't clear to you, the "OS" is the operating system of the computer. A computer can't do anything without an operating system except find, load, & run one. It must come from somewhere, like the hard disk drive inside a Mac, or an external USB drive. The internal drive usually has Mac OS X on it. If Lion or Mountain Lion was installed on it, it should also have a tiny little Recovery partition, which contains a "mini" version of the OS that can only run the few applications included on that partition.

(A partition is a subdivision of a hard drive that acts like a separate disk. So if Mountain Lion is installed, the main partition, called the startup disk, has the Mountain Lion OS on it, & the hidden Recovery partition has the "mini" OS & the apps it can run on it.)

If you erase the startup disk (which it seems you have done), the Mac can't possibly start up from it, so to do anything you have to start up from another disk, like the USB stick Tony T1 suggested. And to start up from that, it has to have an OS on it too, which is where the Recovery partition is useful. Assuming it is still on the internal hard drive, you can start up from it (by holding down the Command & R keys when you start up the Mac) & install the Mountain Lion OS on the USB drive.

If instead you reinstall Mountain Lion on the regular startup disk inside your Mac, that will write over at least some of the data you might otherwise be able to recover. (When you "erase" a disk normally, the data isn't actually erased; instead, the space on the disk where that data is stored is marked as unused, so subsequent writes to the disk may use it, replacing the old data it contained with the newly written data.)

Since there is no way to predict how much old data gets replaced (because it could be stored anywhere on the disk), there is no way to predict how much of it remains & could be recovered, except by using recovery software like Data Rescue 3.