I've got some older hardware that needs a memory upgrade, and I was trying to determine what RAM would be the fastest on the platform. 

My platform takes DDR2 667MHz which is (slightly) more expensive than DDR2 800MHz for example. So here are the options:

```
 Frequency | CL (CAS Latency) | Latency (ms)
 -------------------------------------------
 667MHz    | 5                | 15ms
 800MHz    | 6                | 15ms

```

Which is all well and good - they look like the same absolute speed.

**But my question is**, does the memory operate synchronously with the CPU and share the same clock speed, or does it return as soon as it can? 

e.g.If it's synchronous, then when I put the 800MHz chip into my computer, then it will be running at 667MHz with a CL of 6, which would be slower.