Ok you want to back up your 120gb ps3 HDD, so you go to your local store and buy a 250gb external HDD connect it to your PC and format it to FAT32 the file system your PS3 uses and you get a grand total of 32gb? This is because windows will only format FAT32 to 32gb unlike NTFS which is a maximum of 16tb. Your now sitting there scratching your head wondering where you went wrong and try to format again and again. You want a solution? Good the link is below will format a 250gb HDD in around 5 mins just click the large image. If you get stuck comment and I will try to help.
There is a long-winded way around which is delete the partition and make a RAW partition and then format using DOS and a few other strange commands but the application I have found works the best and saves you time.
Oh and if you get an idiot in a store telling you FAT32 will only format to 32gb use the application then take it back to the store connect it to a PC and rub his face in it.