First time i read some information about SSD's, i was surprised to learn they internally use NAND flash chips. This kind of memory is generally slow (low bandwidth) and have high latency while SSD's are just the opposite.
But here is how it works : SSD drives increase their bandwidth by using several NAND flash chips in parallel. In other words, they do some data striping (aka RAID0) across several chips (done by the controller).
What i don't understand is how SSD's drives have such a low latency, whereas they are using NAND chips? (or at least lot better than what a typical single NAND chip would do)
EDIT: I under-estimated NAND chip capabilities. USB drives, while powered by NAND's are mostly limited by USB protocol (which have a pretty high latency) and the USB controller. That explain their poor performance in some cases (as prunge explained).