How are DDR-3 data rates defined?

[dragonfury]

Hi all,

Why are the data-rates for DDR3 defined as 1066MHz, 1333MHz instead of simply 1000MHz, 1300MHz. Why is the increment in data speeds not round off? Is it some standard that was set in history?

 

[FvM]

They are fractional numbers referred from 400 MHz.

 

[dragonfury]

Why are they fractional? Any reason?

 

[FvM]

Clock generator frequency ratios are fractional, too. Obviously, the specification is historical somehow.

If you don't like it, use 1000, 1300 MHz etc.

 

[dragonfury]

I just wanted to know if there is some logical reason behind it.