Surface scan on TechTool Deluxe.

It is unreliable. If you wish to check or repair the drive do this:

Repair the Hard Drive and Permissions

Boot from your Snow Leopard Installer disc. 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 ** loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the ** 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 ** 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 ** and return to the installer.

If ** reports errors it cannot fix, then you will need Disk Warrior and/or Tech Tool Pro to repair the drive. If you don't have either of them or if neither of them can fix the drive, then you will need to reformat the drive and reinstall OS X.

TJ94 wrote:

Surface scan on TechTool Deluxe has said that there were 48 errors, why is this? Is this due to the Internet or is it internal or is it just something that happens?

A surface scan identifies bad sectors on the drive where data won't be reliably read or written too.

Normally as one writes data to the drive if it can't write to it then the driver software maps off that bad sector and uses another.

However at the factory, data is likely injected directly onto the drive, right over the bad sectors and everything which might result in unstable OS X behavior.

If your computer is running fine, then no need however if OS X is unstable, then perhaps some part of OS X itself is written on a bad sector.

There is a simply method to pre-mapping off bad sectors on new hard drives, and that's Disk Utility Erase Security option Zero and format the drive HFS+ journaled. (warning all data will be lost)

You can also do this in a perfectly fine working OS X by using Disk Utilities "Erase Free Space" option and choosing Zero (don't format)

To do it to a whole OS X drive, you need to clone all the data off first using Carbon Copy Cloner, to a external drive, then hold option and boot from the clone, then use Disk Utility > Zero method.

What Zeroing does is writes 0's to every bit on the drive or free space, depending which option you choose.

The driver software for the hard drive will then map off any bad sectors automatically. So with Zeroing your forcing the machine to do it in advance.

As you notice the Surface Scan for TechTool Deluxe was not enabled in the software by default, it's because there are always errors from bad sectors, but the hard drive driver software automatically takes care of them.