All the 'upgrading your Apple TV' tutorials say I need a 2.5" IDE drive, but there seem to be very few of them, they have low capacity and they are very expensive.
I've found a 1TB internal 3.5" SATA drive for £75. Can't I use that?!
If you wish to use a 2.5 inch SATA drive and keep your AppleTV as a nice little self contained unit (but you are currently limited to 500Gb), use this link..........https://forums.macrumors.com/threads/683178/
If you want to go for a giant AppleTV and are prepaired to have an external drive with a SATA cable hanging out of your AppleTV, use this link (commonly referred to on Macrumors as the eSATA mod).....https://forums.macrumors.com/threads/683178/