The answer is: A 2.5" PATA (=IDE) disk. Today (2012) they are somewhat more expensive dollar to GB than SATA and newer disk types, but they can be aquired most places, and often cheap, if they are used... You could also buy an SSD (Solid State Disk) to minimize power consumption and build-up of heat in you Apple TV 1st gen. 64GB IDE MLC cost btw. $50 and 100. Possibly avoid the Chinese direct-to-consumer SSDs found on Amazon in bundles - Transcend's SSDs are also made in China, but at least you have a place to complain, if your's stop working. SSDs of the type MLC are slower than SLCs, but at about 1/3 of the price of a type SLC. Cloning your old hard drive onto an SSD takes two partitions on the SSD, and this writing back and forth between the two partitions on the SSD are perceived by some as slower than using a spinning hard drive.