There have been roughly three generations of double data rate RAM
for desktop and laptop computers:
DDR, DDR2 and DDR3.
The number following each is usually the effective clock rate:
e.g. DDR2-800 has a raw memory clock rate of 400 MHz
that transmits data twice per tick -- hence the "double data rate".
A second convention has developed, which simply multiplies
that effective clock rate by 8 bytes per tick:
thus, 800 MHz x 8 bytes per tick = 6,400 Megabytes per second.
And, that memory has come to be identified as PC2-6400
where the "2" in "PC2" identifies DDR2.
So, let's switch to DDR3, using the same approach:
PC3-8500 was derived by multiplying 8 by some effective clock rate:
so, just divide 8500 / 8 = 1066 (roughly), or DDR3-1066 e.g.:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820134784&Tpk=N82E16820134784
Similarly,
PC3-10600 / 8 = DDR3-1333; DDR3-1333 x 8 = PC3-10600
PC3-12800 / 8 = DDR3-1600; DDR3-1600 x 8 = PC3-12800
Notice how the latter specs are exactly TWICE the specs for DDR2-800:
i.e. 800 x 2 = 1600; 6,400 x 2 = 12,800.
Browse around Newegg and search for the strings
"DDR2" and "DDR3" and you'll see plenty of examples
of various raw memory clock rates, identified also by their
"PCx" nomenclature.
I hope this helps.
MRFS