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What does a hard drive do?
Storage is the hard drive’s responsibility. Everything you keep on your computer is on a hard drive. Not just documents, pictures, music, and videos. Your programs, your preferences, even your operating system—they’re all stored on your computer’s hard drive.
If your hard drive is damaged, you can lose it all. That’s the sad truth. Which is why most people have a backup system. They get another hard drive and copy all their important files onto that.
How much capacity do you need?
Everything that can be saved on a hard drive is measured in terms of its size. Text is very small, pictures are larger, music is larger still, and video is the largest of the bunch.
A hard drive is like a scale. It doesn’t know the difference between things that are on it; it only knows their size. But instead of pounds, a hard drive measures things in terms of megabytes (MB), gigabytes (GB), and terabytes (TB.)
Roughly speaking, a megabyte is 1 million bytes, a gigabyte is 1 billion bytes, and a terabyte is 1 trillion bytes.
So what does that mean for you?
If you need to transfer files between computers or a drive to back up just some of your files, you can get by with a smaller drive (250GB to 500GB).
If you want to back up your entire computer, or even several computers, or if you work with a lot of video and audio files, you’ll want a larger drive (1TB or larger).
Will your drive work with a PC or a Mac?
Any Seagate drive works with either a PC or a Mac. Some drives are already formatted to work with one or the other. But any drive can be reformatted to work with either type of computer.
IMPORTANT: If you reformat a drive, every single file on that drive is erased. So make sure you copy your files somewhere safe before you reformat.
It’s more difficult to use the same drive on both a PC and a Mac. The short answer is, they’re not really compatible. The more detailed answer is that, in a few specific circumstances, you can do a few specific things. You can read about those here. Related from Freeipadapp's blog.