How can I format my external hard drive to use on my PS3?

Formatting deletes everything on the drive as part of the process. PS3s can only read FAT32 format external drives. Your drive is probably formatted as NTFS. NTFS is very much owned by Microsoft, which makes it a pain to include it in a non-Microsoft product. Its an industry politics and intellectual property issue. FAT32 has a limit of 4GB per file (so if you have a bigger file you must split it in two). Modern versions of Windows won't format a FAT32 drive bigger than 32GB. This is an artificial limitation. If you want to format a larger drive as FAT32, you need a third party partition editing utility. As a Linux guy, I like GParted. GParted doesn't run on Windows, but you can run it standalone off a bootable CD. If this doesn't appeal, then you will need to look at some of the other similar programs available (see link below). You don't have to format the whole drive as FAT32. You can partition it into two partitions and have one FAT32 partition for your PS3 (and any other non-Windows systems you come across) and an NTFS partition for your PC. These partitions will show up as two separate "disks" on most systems. Many partition editors will let you "shrink" the existing NTFS partition, leaving your files intact, and put the new FAT32 partition in the space that creates. However, most carry a "back up any important files" warning for anyone who is doing this.