External Harddrive

Im planning on purchasing an external hard drive so I can save all my data onto that drive as back-up. Is it necessary to format the new drive I will be getting and if so, do I have to format it on a Mac or PC?

it doesn't neet to be formatted. it should com formatted to fat32 which the 4k can read and write too. I bought the el cheapo compusa 80G drive and it works well with the 4k.