What is DRW-1S81?

I dont’understand!! How many kind of LDW-811S there are?
LDW-851, DRW-1S81…finish?
If i buy a DRW-1S81 where i find the firmware update? Is a good dvd-writer or is a different version of the LDW-811S?

It is an OEM LDW-811S. You can find firmware for it here: http://www.4kus.com.tw