I recently went into a local Mac Store that accepts old MacBook Pro trade-ins for store credit. As part of their trade-in evaluation procedure, they have their technicians thoroughly test the performance of the machine and probe for any serious problems. Fortunately, everything tested fine "except" they are reporting that the hard-drive has one bad data block which is enough for them to not be able to accept my trade-in in the computer's current condition. They will accept it once the hard-drive gets replaced. Ever since I've owned my MacBook Pro that I bought new in July 2010, I've never had any problems with the computer. I realize of course a critical problem can arise with a computer the older it gets if used on daily, regular basis and I know I am no longer under warranty. I have no problem buying a new hard-drive for my MacBook Pro and installing it myself to save part and labor costs, but I want to verify for myself the claim that there is a bad data block on my hard-drive. What software is best recommend for evaluating the integrity of a hard-drive that I can run myself to verify this problem? I would strongly prefer freeware solutions please or something extremely cheap.