Considering Something:

[Linarish]

I have an Alienware X51 computer, it has four gigabytes of RAM.

Now, what I'm considering is I have my old computer, a Pavillion p6000 series,
P6644y HP Pavilion p6600 Desktop PC series -  HP Pavilion p6644y Special Edition Desktop PC Product Specifications - c02575965 - HP Business Support Center

The ram is DDR3 and looking up from these sources Computer memory upgrades for Alienware X51 Desktop/PC from Crucial.com Memory:
DDR3 PC3-12800, DDR3 PC3-10600
Memory Type: DDR3 PC3-12800, DDR3 PC3-10600, DDR3 (non-ECC)
Maximum Memory: 16GB
Slots: 2

Would it be possible for me to put the ram in my P6644y into my Alienware?

 

[BikerEcho]

that would be possible.
check to see what speeds the different RAM modules are running at.
if the HP's RAM is slower then the Alienwares RAM, the Alienwares RAM will decrees in speed to mach the slower modules forom the HP.

---------- Post added at 12:35 PM ---------- Previous post was at 12:33 PM ----------

WAIT...
it seams like the Alienware only have 2 RAM slots on the motherboard.
so you can't have both the alienwares ram and the HP's RAM