Cpu memory compatibility

[Ancient Submariner]

Hello,
I have an Emachine MS-7207 with AMD processor 2.1.
Can I mix a 1gig PC3200 -400 DDR with any of the following?
KVR 400/512, 512 DDR 333 OR PC3200 256MB DDR CL3.

 

[saaiello]

You can mix ram yes but it will run at the speed of the slowest chip

 

[Ancient Submariner]

The reason I was asking is the different readings I get. When in "My Computer" it says I have 2.5 gig approx and when I run "mem" in dos cmd, I get 655360 conventional memory with 1 gig extended. What's the difference?