Can someone explain to me the difference of ddr2 800 vs ddr2 667.

[mellondust]

This question is based on me going to upgrading to a conroe system.(as soon as there is a better motherboard selection) I don't understand how memory speed relates to the front side bus speed or performance. I thought I did, but I'm not sure now. Is the front side bus speed determined regardless of the memory speed? Lots of people are getting conroe systems and using ddr2 667 memory, why not get ddr2 800 if it can be used, or is price a factor. It seems to me that you would want to be running your rig with a 1066 fsb and the fastest memory your mother board will support. Please help me understand this relationship. If it is a price issue, is that where overclocking your memory comes in?

thanks

 

[Bobthelost]

Price performance is the reason. While you do get better performance running at 1:1 the premium you have to pay to do so is far greater than the performance increase you get from doing it.

Think of it as a motorway, if you're not getting trafic jams with 4 lanes then going to 8 lanes won't do anything. The DDR 800 has a higher bandwidth tahn 667, which doesn't help much as it's not clogged up, and if the latencies are the same a slightly faster response time (like increasing the speed limit on our motorway) which does improve things a bit.

Theres' some good articles on this topic in the main site if you want to go look.

 

[Raider1284]

With the new conroe systems they benefit most from having a 1:1 ratio with respect to the FSB and the memory speed. So if you are looking for a FSB over 333 your are going to have to start overclocking your 667 ram to keep a 1:1 ratio. But if you had 800 ram you could run it 1:1 without overclocking the ram all the way to 400FSB! You double the FSB to get the memory speed. Also alot of the new 800 ram will do 1066 quite easily with relaxed timings which would allow you to keep a 1:1 ratio up to 500FSB!

Hope this helps.

 

[vulcanman]

The front side bus on a Conroe system is 1066MHz ... so, per Raider1284 ... the ram has to be 2132 MHz ?

If so, why is Dell only offering 533MHz and 667MHz DDR2 chips for their Conroe configuration ?

TIA

 

[Raider1284]

the FSB you see in the bios is multiplied by different ammounts. The FSB is doubled to get the actual ram speed. While the FSB is multiplied by 4 to get the cpu FSB. At stock speeds the fsb is 266 in the bios, so 266*4 = 1066.

Hope this helps.

 

[Bobthelost]

DDR2 800 runs @ 200mhz. It's quad pumped. So to get a chip with a 266 FSB to be working @ 1:1 you'd need a DDR2 1067.

 

[imported_hardwareguy]

DDR2 isn't quad pumped, it's just doubled. If your system clock is 266Mhz (default for Core 2), then your ram will run at 533Mhz (266 x 2), your FSB will read 1066 (266 x 4), and your processor will run at whatever it's multiplier is x 266 (on the e6300 it is a 7x multiplier so at a 266Mhz system clock it will run at 1866Mhz). If you overclock to 400 your ram (at 1:1) will run at 800Mhz, your FSB will run at 1600Mhz and your CPU (if it's an e6300) will run at 2800Mhz.

 

[Raider1284]

Really? Because i have seen many people with 400*8 for the e6400 and they all are getting ddr 800 speeds when they keep the 1:1 ratio.

 

[imported_hardwareguy]

Originally posted by: Raider1284
Really? Because i have seen many people with 400*8 for the e6400 and they all are getting ddr 800 speeds when they keep the 1:1 ratio.

Yeah, that's correct. I have a e6400 @ 400Mhz system clock right now. My ram is at 1:1 and running at 800Mhz.

 

[Bobthelost]

Originally posted by: hardwareguy
DDR2 isn't quad pumped, it's just doubled. If your system clock is 266Mhz (default for Core 2), then your ram will run at 533Mhz (266 x 2), your FSB will read 1066 (266 x 4), and your processor will run at whatever it's multiplier is x 266 (on the e6300 it is a 7x multiplier so at a 266Mhz system clock it will run at 1866Mhz). If you overclock to 400 your ram (at 1:1) will run at 800Mhz, your FSB will run at 1600Mhz and your CPU (if it's an e6300) will run at 2800Mhz.

DDR = Double Data Rate ie dual pumped.
DDR2 = Double Data Rate X2 ie quad pumped.

When you had DDR 400 (PC 3200) it ran 1:1 with a FSB of 200. Just think about it for a few seconds.

 

[imported_hardwareguy]

QDR is quad pumped, but that's not really around yet. DDR and DDR2 are both double pumped. Here's a quote from the wikipedia article on DDR2:

"Unlike SDR, both DDR and DDR2 are double pumped; they transfer data on the rising and falling edges of the clock, at points of 0.0 V and 2.5 V (1.8 V for DDR2), achieving an effective rate of 200 MHz (and a theoretical bandwidth of 1.6 GB/s) with the same clock frequency."

http://en.wikipedia.org/wiki/DDR2_SDRAM
http://en.wikipedia.org/wiki/Quad_Data_Rate_SDRAM

 

[Bobthelost]

http://www.xbitlabs.com/articles/memory/display/ddr2-ddr_2.html

DDR 400 operates at a core frequency of 200mhz
DDR2 800 operates at a core frequency of 200mhz

Read the discussion of that wiki entry, it's more educational than the article itself.

DDR2 uses some QDR transfer methods, though is still very much based on DDR technology

Hmmmm...

 

[imported_hardwareguy]

So when I set my System Clock to 400Mhz and CPU-Z says my DDR2 RAM is running at 800Mhz it's actually running at 1600Mhz?

 

[zephyrprime]

DDR2 is not quad pumped. Yes, it's core speed is 200 and it's datarate is 800 so there is a 4:1 ratio but it is nonetheless not quad pumped. It is double pumped like DDR1.

Being quad pumped means having the ability to send 4 bits per pin per clock tick and DDR2 does not do that. DDR2 attains it high speed by having and internal io interface that runs at double core clock speed. The IO interface then reads 4 bits per core clock so it can achieve it's datarate. DDR1 reads 2 bits per core clock.

 

[skinnyj]

so great i think im more confused then before i clicked on this thread.

My question goes alont with the OP's I understand that price/performance may not be on par for 667 to 800, but im trying to build somthing that will last 2 yrs or so with only upgrading the gpu. Meaning that if i cant use 667 to overclock very well i rather spend the money on 800 now so I can oc it? does that sound logical ?

Or is 667 perfectly fine for ocing? and i should just resell the 667 later for some 800 or somthing? btw i will be getting a e6400 thanks

 

[Bobthelost]

Well despite being proven mostly/partly wrong i'll chip in again.

You can overclock the CPU without overclocking the RAM. You get more performance if you overclock both, but you don't have to. As such you can get the 667 and it won't make a difference to how high you push the OC on your CPU. Faster RAM might be helpful in the future if the sucsessor to C2D is more RAM hungry, but who knows.

I'd go for 667 myself (hell i did).

 

[skinnyj]

thanks bob. I guess im just wondering, if i get 667 i can still overclock and everything will run good? im not trying to hugely oc but i would like to get like 2.8 or somthing out of my e6400 thats possible?

 

[Bobthelost]

Yes. There are things called RAM dividers that let you operate the RAM slower than 1:1. I know i'm right on that one

As to how high an OC you can expect i don't know, (i try not to read the threads as i'll get jealous and upgrade again )

 

[imported_hardwareguy]

Originally posted by: skinnyj
thanks bob. I guess im just wondering, if i get 667 i can still overclock and everything will run good? im not trying to hugely oc but i would like to get like 2.8 or somthing out of my e6400 thats possible?

Most people have been able to get that high with the e6400. I've got 3.2Ghz out of my e6400 right now with Patriot DDR2-667. I've got my system clock at 400Mhz and my RAM at 1:1 with 4-4-4-12 timings. I think you'll be able to easily get to 2.8 but it depends on the particular chips/mobo you have.

 

[lxskllr]

Here's my $.02. I'm going to get ddr2 800. That'll give me more headroom for my overclock, and I may be able to tighten my timings some. If nothing else it future proofs the ram somewhat without adding significantly(to me) to the cost.

 

[Skeeedunt]

Are there any benchmarks that evaluate the impact of running C2D with a divider? Is it considered a non-issue as it was with A64's?

 

[imported_RedStar]

http://www.madshrimps.be/?action=getarticle&number=2&artpage=1963&articID=472

re: changing timings -nice graphs and analysis

 

[Skeeedunt]

Originally posted by: RedStar
http://www.madshrimps.be/?action=getarticle&number=2&artpage=1963&articID=472

re: changing timings -nice graphs and analysis

perfect thanks

 

[Hidden Hippo]

I got DDR2-800 and to be honest I'm not that happy with it. I don't want to overclock my processor at the moment, but on my board, it only seems to work if you have a 1:1 ratio. This means that I either have to downclock my RAM from 800MHz to 533MHz (not ideal, but it'll have to do until Abit fix this issue) or I have to overclock (again not ideal since I don't want to fry my processor).

 

[Bobthelost]

Not wanting to overclock is fine (sensible even ), but unless you overvolt heavily it's not going to be instant death, merely a few years knocked off the life span. If you don't raise the Vcore then it's not going to even lower the lifetime noticably.