What exactly is an High Density RAM?

Ajay Shanmuga

Honorable
Jan 3, 2014
34
0
10,530
Hey all! I was thinking of upgrading my PC, and I have an MSI MS7379 mobo, and coming to memory...I can't find a single 4GB ddr2 stick(are they truly available). But, while searching for sticks in eBay, I came across these strange 'HIGH DENSITY RAMS'. What are these actually? And the product page says that it should be used only for AMD Mobo. But, can I use it for mine? Will it work? What are the pros and cons?
Suggestions are welcome. Thanks in advance!

This was thing I was talking about...
http://m.ebay.com/itm/4GB-DDR2-800Mhz-PC2-6400-DIMM-240Pin-For-AMD-CPU-Desktop-Memory-RAM-Chip-/361416529965?nav=SEARCH
There are also similar sticks like this one.