I have the above Western Digital Black 500GB drive (WD5001AALS-00E3A0) build date August 2010.
When i first got it, i thought it felt a little heavy for a single platter disk, but didn't think much of it. I used yertech.blogspot.com 's collection of Western Digital platter sizes to see it reportedly has 1 platter/2 heads.
However, my benchmark read/write from HDtune shows maximum read/writes as 129MB/sec and minimum as 97MB. (here is the read. the write is pretty much a mirror image: http://i54.tinypic.com/1zlr9f5.png)
The graph simply doesnt look like a typical HDtune for a single platter disk from my experience. in fact it looks like half - without the tapering off on the end when it reaches the 500gb mark.
Does this looks like the drive most likely has 2 500GB platters, which are shortstroked to make 500GB in total?