CAS Latency vs. Clock Speed

[AMD Lover]

So I'm looking at two different skews of RAM for my laptop. One set it 32GB (2x16GB) DDR4 2400Mhz CAS 14 and the other DDR4 2666Mhz CAS 16. Are they going to be about equal in performance?

[WereCat]

Chances are that your laptop doesn't support 2666MHz RAM... depends on motherboard and CPU.

[Jurrunio]

I guess DDR2 is actually DDR4?

 

2666MHz CAS16 is faster than 2400MHz CAS14, but why bother with fast RAM when using Intel CPU. Just get the cheaper one (if they cost the same, 2666mhz one)

[xentropa]

CAS latency (column address strobe) is the number of clock cycles between activating the word line and when the sense amps can pick up the signal.

 

CAS 14 and 2400mhz means it takes 14 clock ticks at 1200 mhz (half due to DDR)

 

The actual latency is 14 * 1 / 1.2 billion = 11.6 nanoseconds

 

For CAS 16 @ 2666 mhz, it is 16 / 1.33 billion = 12 nanoseconds.

 

Actually, CAS 14 at 2400 is slightly faster.

[Imbellis]

18 minutes ago, AMD Lover said:

So I'm looking at two different skews of RAM for my laptop. One set it 32GB (2x16GB) DDR4 2400Mhz CAS 14 and the other DDR2 2666Mhz CAS 16. Are they going to be about equal in performance?

Technically, as @xentropa said, the 2400 RAM is slightly faster.

4 minutes ago, xentropa said:

~Snip~ (half due to DDR)

 

How does that work?

[AMD Lover]

19 minutes ago, WereCat said:

Chances are that your laptop doesn't support 2666MHz RAM... depends on motherboard and CPU.

There's people saying it does and it pulls up on Crucial's compatibility list.

[AMD Lover]

18 minutes ago, Jurrunio said:

I guess DDR2 is actually DDR4?

 

2666MHz CAS16 is faster than 2400MHz CAS14, but why bother with fast RAM when using Intel CPU. Just get the cheaper one (if they cost the same, 2666mhz one)

Yeah DDR4, lol

[xentropa]

10 minutes ago, Imbellis said:

Technically, as @xentropa said, the 2400 RAM is slightly faster.

How does that work?

A clock is a square wave electronic signal.

 

DDR is an advanced circuit technoligy which can trigger an action on the rising AND falling clock edge.  So you get two "actions" per cycle as opposed to normally one.

 

The 2400mhz advertised is the actions per second.

[AMD Lover]

2 minutes ago, xentropa said:

A clock is a square wave electronic signal.

 

DDR is an advanced circuit technoligy which can trigger an action on the rising AND falling clock edge.  So you get two "actions" per cycle as opposed to normally one.

What about 2666Mhz CAS 15. Found one kit that meets that spec.

[xentropa]

1 minute ago, AMD Lover said:

What about 2666Mhz CAS 15. Found one kit that meets that spec.

Should work.  Its when you overclock RAM there are no guarantees.

[Nena Trinity]

Depends on the CPU some prefer CAS over MHz and some like MHz uber alles.