Any Drive over 32 GB is supported by Medicat.
We SRONGLY suggest using a USB 3.0 or above as using usb2 will SEVERLY damage the speed of your install and some tools may fail to boot.
That being said Medicat will boot with computer that only has 2.0 slots.
Matt And Jayro strongly suggest using a USB SSD enclosure if you plan to use Medicat on a semi regular basis.