these are tradeoff between DDR2 (for higher speed, but higher read latencies) vs DDR (lower speed + read latencies).  

so if u make the bus speed the same for both, then DDR2's higher latencies will make it slower than DDR. 

http://www.diffen.com/difference/DDR_vs_DDR2

and a technical comparison charts in numbers:

http://www.freescale.com/webapp/sps/site/overview.jsp?code=784_LPBB_DDR


On Mon, Jun 3, 2013 at 2:39 PM, devendra.aaru <devendra.aaru@gmail.com> wrote:
Hello,

I have two different types of hardware, one with DDR SDRAM and another DDR2,
i tested them with bw_mem tool for write bandwidths, seems that at
higher writes of  >512kbytes the DDR is faster than the DDR2(more than
40%). But when compared to reads, DDR is slower (more than 50%). I
couldn't find any reference that explains why. AFAIK, the DDR2 works
double the faster rate than the DDR.


any ideas?

Thanks,

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Regards,
Peter Teoh