Confused about Western Digital

I am about to buy some harddisks. What is the difference between the WD20 EARS, EZRS, EZRSDTL and EZRX?

Platters? Density? rpms?

OK, be warned: trying to decipher model numbers can get you into trouble as manufacturers sometimes change their mind about what the letters mean so bare with me.

http://www.wdc.com/en/products/products.aspx?id=120 (Click on Specifications)

http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-701229.pdf (More information comparing models)

As far as I can tell: E= Energy Efficient (GP Drive), R = 64MB Cache, X = SATA3, RX/DX/RS = Advanced Format Drives

The A & Z in the model numbers gets a little more confusing, if someone can help clarify that would be great. The only difference I could find was:

A = Uses less power (0.7W sleep, 3.3Widle, 5.3W r/w) and is lighter (1.4lb/0.64kg)

Z = Uses more power (0.8W sleep, 5.5W idle, 6W r/w) and is heavier (1.61lb/0.73kg)

My guess is A's have one less platter- however the external size of the drives is exactly the same and the specification sheet doesn't appear to list # of platters anywhere. Other than this the drives appear pretty much identical. If you can get your hands on an EARX then that would be the one to go for.

The EZRS appears to be identical to the EZRX other than the interface (EZRS = SATA2, EZRX = SATA3).

The EZRSDTL is rare in Aus and I can't find much at all about this model. Most of the sites offering specs etc. aren't in english and WD's site doesn't even list it.

Hope this helps

Platters? Density? rpms?

Just to add:

An "A" model drive is likely to have less platters than a "Z" model of the same size and will therefore have a higher density per platter. All of the WD GP drives are 5400RPM.

The DTL is likely to be the EU assembled drives.