Adding memory

[MRGOOCH]

I am in the process of building a new computer.I will have 2- 4 GB matched memory sticks
and would like to include my older 2- 1 GB matched memory sticks in the remaining two slots. Can I do this?

 

[MRGOOCH]

My old memory is DDR2 800 PC-2 - 6400
New memory is: DDR3 PC3 -12800 1600MHz

 

[Cerb]

No. One is DDR2, the other DDR3.