20: Zero Erase and Fresh install OS X (advanced)
Warning: permanent data destruction on the entire drive or partition selected. No recovery possible. All programs, files and operating system gone.
Wipes everything method. Everything erased, the hard drive bad sectors mapped off, everything new except files from storage drive, no clone or TM restores unless you know it's not corrupted.
This method is reserved for hard drives that the file structure has gone bad, pinwheel issues that isn't resolved by any other manner (bad sectors), malware, corrupted EFI or anything super serious that Disk Utility gives and unable to repair the drive.
The methods are the same as #8 Reinstall Just OS X, however before you install OS X again, you first select Disk Utility and the drive or partition and
On 10.6: Erase > Security Option > Zero All Data, then click Erase.
On 10.7: Zero Erase is one selection from the right, then click Erase.
It's going to take some time, when finished, one installs OS X and then go about installing programs and returning files from backup, or restoring from a clone or TimeMachine drive.
Note: SSD's boot drives don't have a Secure Erase function, only Erase.
10.7+ you may have to create a 10.7 Recovery USB to catch the entire drive.
Your basically booting from the Recovery HD partition which is on the same drive as MacIntosh HD or BootCamp, so your erasing one partition from another on the same drive.
However some people's drive problems extend outside the MacIntosh HD and BootCamp, into the hidden Recovery, HD, EFI or GUID partition map, therefore the only solution is to erase the ENTIRE from a outside source. If you can boot into OS X you should try to make this bootable Recovery USB, you may need to use another Mac to copy that Recovery HD.
If you can boot into only Recovery HD, then your should create this and later can use Carbon Copy Cloner to clone back onto the internal drive after the drive has been completely erased to catch all partitions, hidden and otherwise.
Newer Mac's have Internet Recovery which one can boot and use just like Recovery HD, it's downloaded off the Internet and can be used to erase the drive in it's entirety as well.
If you need more security in data deletion, I read this
What OS are you using?
How large is the internal Hard Drive and how much space are you using (Click on the HHD icon in the upper right hand corner COMMAND 'I').\
Are you trying to delete all data on the HDD or just some?
Look at this Apple support article and see if any of this information helps your situation:
Please DO NOT zero erase and reinstall yet! That's an absolutely ludicrous suggestion to jump straight to without trying anything else. Even if erasing the hard drive should prove to be necessary, a zero erase is not necessary.
If your hard drive doesn't have enough space, the obvious answer is to simply delete some stuff. You say, though, that the trash isn't emptying. Just to verify, you have stuff in your Trash, you choose Finder -> Empty Trash, you hear the "empty trash" noise, and then everything that was in the Trash is still there... is that correct?
If so, there may be something wrong with your hard drive, or it may simply be too full for the system to operate. (If the hard drive gets too full, it can cause serious problems, including corruption and data loss.) So, first thing to do is hold down the shift key while starting up. This boots into safe mode, which has the side effect of deleting some caches. That should give you a tiny bit of breathing room. Now try emptying the trash.
If it still doesn't work, you need to try repairing the hard drive. How you do that depends on what system you have. If you have Lion (Mac OS X 10.7.x), hold down command-R at startup, then select Disk Utility when you're given that option. If any older system, insert your Mac OS X install disk and restart, holding down the 'c' key during startup. Then select your language, and then choose Disk Utility from the Utilities menu. Either way, once in Disk Utility, repair your hard drive. If repairs are successful, try rebooting and then emptying the trash again.
Once you've done that, you'll need to make more space. You should have about 10-15% of the hard drive free. So start deleting stuff. Start with anything in your Downloads folder.
If repairs are not successful, you may be able to recover using something like DiskWarrior. But, if you have backups, you might do better to just erase the hard drive and restore from an older backup.
i have Mac OS X 10.3.5
the hd used to have 0 free space but i tried to restart and hold down the shift key for safe boot
and now i have 90.2 mb available
i guess if i do that again many times ill have more & more space available
btw i did well in my exam i just came early to school and revised
and maybe when i have free time ill take this crappy computer to a worker to format it...
Repeating safe boot isn't going to keep freeing up more and more space. You've got to delete some stuff. A LOT of stuff, actually! You're lucky if this is the only problem your computer is having... letting free hard drive space go all the way to zero can cause many problems, including data corruption.