it basicaly compares USB3 and SATA2 which USB3 is 4.8Gbps and SATA2 is 6Gbps (giga bits per second)(not bytes) which is /8 to get bytes, not bits.
there are 8 bits in a byte so 16 bits will be 2 bytes, if you get my drift. and bytes are used for space where as bits are used for speed. hence why Gbps(Giga Bits Per Seconds) and GB (Gigga Bytes)are diffrent as can be seen here. http://en.wikipedia.org/wiki/Data_rate_ ... per_second
so basicaly in laymans terms saying that your downloading at 2 giga bytes is wrong, (like if you driving a car) it means (in an hour) how fast you driving and you just say 20 miles, when infact you mean 20 MPH or 32.3 KMP (for our USA friends ) or vice versa saying what speed did you drive and you say, well i driven at 20 MPH when you means you drove at 20 miles. This might be a bit long winded but i hope you get my drift, im an IT guy and i get alot of customers confused about the whole Gbps and GB thing (one is distance one is speed, like Miles Per Hour MPH or just Miles, ones distance ones is speed) so dont think im assulting you inteligence i just want to make it so your understand what your buying! i see alot of people getting ripped offf (as you can imagine in IT)
so i hope i set you off with the knowledge to look for what you want, rather than just an item that some ones says that you think you want! but look at them links and you will gewt a good disivons to deise for you self, but like what what posted on the link above, SATA2 is quicker than USB3 so if possible i would get a Sata Drive rather than SSD.
P.S im only assuming you want a external Drive if note here is a quote.
"the 256GB M4 drive averaged sequential read speeds of 416MB/sec and write speeds of 257MB/sec."
Which TBH is limited by SATA2 speeds, so if i was you i would just get a small SSD for now dont spalsh out for a big espensive one, becuase the tech aint there just yet! i hope this helped!