what's difference between F2-6400PHU1-1GBNT I and F2-6400PHU1-1GBNR I

[anhtrue]

I bought three of F2-6400PHU1-1GBNR I, longtime ago. Now, I want to buy one more to setup dual channel mode with 4 rams. But in my location, they haven't got F2-6400PHU1-1GBNR I any more. They offered me buy F2-6400PHU1-1GBNT I. Without the white case, what's difference between them.

Should I buy F2-6400PHU1-1GBNT I? or buy a new kit ?

[GSKILL TECH]

They use slightly different chips, thus requiring different voltages. I would not suggest mixing them, but instead purchase a 2 x 2GB kit instead.

Thank you
GSKILL TECH