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I have a pair of CL7 RAMs installed on my mainboard. I want to add another pair of of RAMs to my system, but since they are old, I can't find CL7 RAMs of same size and brand in the local market. The closest I can find is the CL9 version of the same brand. Are they compatible, can they work together alright?

Technical details:
Mainboard: Gigabyte P55A-UD3R, rev 1.0 (official page)
Currently installed RAMs: 2x Kingston, 2GB, DDR3, 1333MHz, CL7
The RAMs I want to add : 2x Kingston, 2GB, DDR3, 1333MHz, CL9

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up vote 3 down vote accepted

You can mix these as long as you slow down to the lowest common speeds.
( Read: It will work if you use both modules at CL9 speeds. )

The BIOS will most likely read the supported modes from the chips and auto select this. If that fails you can manually set the timings.

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