There are a few different versions of this drive with slightly different geometries (a few more or a few less sectors) and different buffer memory.
This is the OEM version which is usually supplied in an anti-static sleeve and sold in bulk to computer builders. As such, it will not have the normal retail packaging, fixing screws or the information leaflet. You can buy the screws in packs of about 100 quite cheaply or you may be able to beg a few from anyone who builds or repairs computers. Functionally, there is no other difference between OEM and retail versions. The OEM version tends to be slightly less expensive.
As it does not have the normal protection that the retail pack would normally provide and it has been known for some sellers to do rather stupid things when despatching OEM drives. If you should be a victim to one of these sellers, and purchased via Amazon, I would suggest that you return the drive for refund, purchase from a supplier with more understanding of the product and complain to Amazon!
The distinguishing feature of the Caviar Green series is that the motor speed is not constant. In normal use when writing or reading, it will operate at it maximum rotational speed but when inactive, the motor will slow. This will save a proportion of it its normal wattage. It does mean that the drive needs a moment to reach maximum speed from a lower one.