Is it possible to actually remove files from a hard drive? advice needed pl

Question

Hey guys and gals. i have a G5 Dual 2GHz Power PC with a problem. I recently had to do an archive and install (my second one). after getting thru with this and trying to get back what had been lost i realized that i only had about 90GBs left on my System Hard Drive. I have two drives on my Mac, one for the system, programs and such and one for recording audio and saving Logic and GB songs. The one that is the boot drive and has all the programs on it is the one that is seriously depleted. It seems that i will have to replace a lot of programs to get them to work again after the A&I and i just don't have the room to do so.
So my first question is that if i move files off that drive do i get that space back? Does it actually "get rid' of those files or does it just make them unaccessible? My second and related question is that if i erase the drive does this actually "get rid' of the files and do i get that space back? The reason i ask is that i have heard that you can't actually completely get rid of files on a hard drive. That when you erase a hard drive it it doesn't really erase the drive it just makes them (somewhat) inaccessible.
If i can't get that space back am i correct that i will need to replace the drive to get more space? Is replacing the hard drive a difficult process? I know that i can by an external hard drive but i am uncomfortable with using one for other than back-up or storage space.
any opinions or advice would be appreciated-thanx-gospel

Answer 1

If you did archive and install, your old system files are most likely still in a directory called Previous Systems at the root of the hard drive - IF you don't need anything from there (i.e., your system is working fine), you can delete that folder - it has many files, so it will take a while to delete. Whenever you delete files, you get the space back. What you heard about data not being deleted is somewhat true (see next para), but you'll need special utilities to reclaim the deleted data, so from a normal usage perspective, you DO get the space back when you delete, so you can reuse that space for other files. Archive and Install of Leopard creates about 11 GB worth of files in the Previous System folder, so there is a lot of space you can reclaim on your system drive.
* Here's an over-simplified view of file storage. Normally a hard disk contains random 1s and 0s anyway. Storing a file organizes some of them (a file size worth) to the proper sequence of 1s and 0s. Think of the hard drive as made of many 'slates' on which file data is written. A master slate keeps track of which files use which slates. When you delete a file, the operating system (OS) normally 'deletes' the name off the master slate only and marks the space as free and available (even though the data may still be there on the slates the old file used - that is, the 1s and 0s belonging to that old file - it is marked as free/available). So the OS can reuse the space - this is what was meant by "you get the space freed up when you delete the file." The special data-recovery utilities know the method the OS uses, so they CAN reclaim the data if that space wasn't overwritten by storing other newer files. So really, erasing the whole disk means marking all space as available/free on the master slate. The disk elements always contains 1s and 0s - even when "empty" - just in a disordered way and known to the master slate. Storing a file just puts order into the sequence of the 1s and 0s.
Obviously I took too long typing all that!
Message was edited by: BobZune