I am going to assume you mean a flash / thumb drive and not memory stick since memory stick usually refers to RAM?
Ok, having worked in IT for over 10 years, this is just plain wrong. Sorry, no offence but referring to a DIMM as a memory stick is incorrect and I don’t recall ever hearing this in the industry either.
Anyhow, to the question at hand. The TR’s have a Memory Stick PRO reader, the memory stick pro standard supports a maximum media size of 32GB. Memory Stick PRO High Speed media is backwards compatible with standard PRO readers so these can be used, no problem.
So you could use either the 4GB or 8GB Duo’s currently available. They don’t make full size memory stick’s in the larger sizes any more, but all duo’s now come with fullsize adapters.
MagicGate is a type of hardware DRM supported by the memory stick format, not a format itself. I don’t think it ever took off—maybe used on PSP?