Difference between DDR2-667 and DDR2-800

[bruins004]

Hey guys,

I am curious what is the difference between DDR2-667 Ram and DDR2-800 RAM?

 

[Deleted member 3]

66MHz (133MHz DDR)

And latencies depending on the module.

 

[bruins004]

Is there any reason why you would get DDR2-800 modules over DDR2-667 modules?

 

[Sasqui]

DDR2-667 is rated to run at an actual clock speed of 333.3 Mhz (667/2)
DDR2-800 is rated to run at an actual clock speed of 400.0 Mhz (800/2)

The clock speed of the ram is driven by the motherboard front side bus (FSB), times the FSB:MEM multiplier in BIOS (some boards have lots of options, others none or few).

For example, if you are running a core2 at stock FSB of 266 and you have DDR2-800, to get the memory to run at full speed, you would select a multiplier of 2FSB:3MEM (266FSB *3/2) = 400.00 and 400*2 = DDR2-800.

In the same scenario, for DDR2-667, you could pick 4:5 multi, so 266*5/4 = 333, or DDR2-667...

Of course memory can be overclocked (run faster than rated) and underclocked (run slower than rated).

Clear as mud?

 

[Sasqui]

Is there any reason why you would get DDR2-800 modules over DDR2-667 modules?

If your motherboard has lots of divider options, the memory speed will make a nice difference in system performance, and also give you a lot more options if you are overclocking.

And also, latencies play into the picture as DTBJ said.

 

[bruins004]

DDR2-667 is rated to run at an actual clock speed of 333.3 Mhz (667/2)
DDR2-800 is rated to run at an actual clock speed of 400.0 Mhz (800/2)

The clock speed of the ram is driven by the motherboard front side bus (FSB), times the FSB:MEM multiplier in BIOS (some boards have lots of options, others none or few).

For example, if you are running a core2 at stock FSB of 266 and you have DDR2-800, to get the memory to run at full speed, you would select a multiplier of 2FSB:3MEM (266FSB *3/2) = 400.00 and 400*2 = DDR2-800.

In the same scenario, for DDR2-667, you could pick 4:5 multi, so 266*5/4 = 333, or DDR2-667...

Of course memory can be overclocked (run faster than rated) and underclocked (run slower than rated).

Clear as mud?

That makes it a little clearer.
So what would the best multiplier be (I am guessing 1).

So due to that, that is the reason why DDR2-800 memory is better?

 

[Sasqui]

Yea, 1:1 or 1:2 is definitely the best, the odd ones cause additional "wait states", where the memory controller can be sitting idle waiting for the CPU or Memory to take or give it data.

Having various CPU multipliers helps too. For instance, I have my Core2 at a multiplier that runs it at it's max (around 430 FSBx8) and DDR2-800 memory at 1:1. So the DDR2-800 memory is actually being run faster than rated (roughly DDR2-860 ... 430 FSB*2), but everything is stable... and the fastest machine I've ever used

 

[Deleted member 3]

That makes it a little clearer.
So what would the best multiplier be (I am guessing 1).

So due to that, that is the reason why DDR2-800 memory is better?

The clock speed is simply higher, so it's bandwidth is higher. Normally this is totally useless since no official processor runs 1:1 with DDR2-800 at stock. However when you overclock the memory won't be a bottleneck as fast.