DDR II 667 vs DDR 400

We currently have DDR II 667 RAM on the dedicated server. We're looking to a new server. One of the options only comes with DDR 400 (or DDR 400 registered). Is there a big difference between DDRII 667 and DDR 400? This is for an AMD Opteron 170 or Opteron 248.

Also, if I run CPUZ on the current server it reports the type of memory to be DDR (not DDRII) with a DRAM frequency of 200MHz, CAS Latency 3 clocks, RAS to CAS delay 4 clocks, RAS precharge 4 clocks, cycle time 8 clocks, banks cycle time 12 clocks, command rate 1T, DRAM Idle Timer 16 clocks. Does this match the DDRII 667 that we are supposed to have?

Thank you.

From serverfault pbz

• What kind of server is this? Seems terribly slow. DDR(1) is more expensive than DDR(2) these days if its a new server you should look at the mainanace costs but wow I think I throw away worse pc's than that without looking twice..

  pbz : LOL, yeah, the specs aren't that great, but has been working pretty well for us. The server is from SoftLayer, it's one of their cheaper ones (http://outlet.softlayer.com/).

  Brian Knoblauch : Many times, the specs on server RAM doesn't look as nice as a typical workstation, due to the fact that it may well be buffered/ECC, etc.

  Thomaschaaf : Brian Knoblauch: I have a quad core with 3 Ghu per core 8 GB of ram 4 nics etc.. I wouldn't say thats a bad ass server at all just a regular server which will actaully do something ;)

  Thomaschaaf : http://www.hetzner.de/hosting/produktmatrix/en-rootserver-produktmatrix/ you might also want to try their servers ;) a lot cheaper hosted in Germany though but connection shouldn't be bad just try pinging their site and see how bad it is.

  pbz : I've heard nothing but good things about Hetzner, but unfortunately we need something on this side of the pond (US). They should consider coming over and spice up the competition a little bit.

  Thomaschaaf : We've got a handful of servers there.. really really good.. any reason linode won't work? Why do you need a dedicated machine.. that bad of a processor will feel the same or worse than any vm provider.. ;)
  From Thomaschaaf

• 667 and 400 indicate the bus speed of the RAM; higher is better.

  Then there's also the issue of DDR vs. DDR2; DDR2 is better.

  When it comes to latency, the first number (CAS latency) is the more important of the four numbers; lower is better.

  pbz : I figured it's slower, but how much slower? Are we talking about a huge difference? Thanks.
  From Scott

• It is also important to note the Front Side Bus speed of the processor. If the FSB is 400 then 667 memory will do you no good.

  pbz : How can I find out what the FSB is for the current system? They advertise a 800MHz bus for the "new" servers (http://outlet.softlayer.com/)
  From Jimmie R. Houts

• See question #4 of the page for CPU-Z to see why it might misreport what RAM you have installed. If you eyeball your RAM, most RAM sold in recent years has a sticker on it that says exactly what speed it is.

  You said that CPU-Z reported your memory as:

  • DRAM frequency of 200MHz
  • CAS Latency 3 clocks
  • RAS to CAS delay 4 clocks
  • RAS precharge 4 clocks
  • cycle time 8 clocks
  • banks cycle time 12 clocks
  • command rate 1T
  • DRAM Idle Timer 16 clocks

  Of these numbers, the two with the biggest single impact on memory access speed are the first two above, the front side bus speed (200 MHz x 2 for DDR = 400 MHz) and CAS latency. However, you asked does this mean you don't have DDR-II 667 -- this depends on whether or not your CPU supports a front side bus rate of 667.

  In a comment, you said that this is a server you can't power off or reboot to do this check. So in CPU-Z, look at the SPD tab. SPD (Serial Presence Detect) is a way to read information about the memory from the memory. This should tell you the manufacturer, model, part number, max bandwidth, allowed timings for different bus frequencies, and so on. You can look at each memory slot and tell what kind of memory is in each position.

  In CPU-Z in the "Memory" tab, it just tells you how the BIOS and OS decided to configure memory timings, based on looking at all of the memory chips and based on BIOS configuration. The "SPD" tab tells you exactly what the memory sticks you have are capable of.

  pbz : Obviously I don't know much about these things, so I may say something stupid, but CPUZ reports a Bus Speed for 200MHz. Is this what you're talking about? Thanks.

  Eddie : A bus speed of 200 MHz will mean a "front side bus" (FSB) speed of 200 MHz, which is reported before any doublings are applied. If your bus speed is 200 Mhz, then you are not very likely to benefit from faster memory, but this depends in part on your BIOS.

  pbz : Is there any place I could look for this multiplier? I can't physically look at the server since it's a dedicated server. Going to BIOS is not an option either. Thank.

  pbz : Thank you for your help. In the SPD tab the only thing that's listed is "DDR" and under Module Size 1024 MB. All the other fields are blank.

  Eddie : This means that the memory is a (most likely) older one with SPD. Which means the only way to truly know what kind of memory it is is to eyeball it. It would guess that it's probably DDR-400 though.

  Eddie : Everything I can find suggests that the Opteron 170 and 248 can only use DDR memory, and not DDR2. Don't take this as definitive, but my search results suggest this. AMD moved to DDR2 memory later than Intel.

  osij2is : I'll save my energy as Eddie has sufficiently answer this question. +1 on the CAS latency, Eddie. Everyone typically understands speed/MHz, but most people forget about RAM timing which in servers is very critical.
  From Eddie

• The speed difference will be absolutely nil. Even in applications like games that are sensitive to memory bandwidth, there's little if any real-world difference between DDR-400 and DDR2-667, because of DDR2's increased latency.

  You don't mention what the server is doing, but typical server tasks (web, mail, database, etc) are CPU- and/or network bandwidth- and/or IO-bound. Memory bandwidth makes little or no difference for those tasks. The bandwidth of DDR2-400 is something like 3.2GB/sec and unless your server is part of a render farm or is doing certain kinds of science work, you're simply not throwing around anywhere near that much data per second. Unless you've got a fairly pricy SAN or SSD array, your drives can't even hope to read or write 320MB/sec per second, and that's only 10% of DDR-400's bandwidth.

  As others have said, DDR2 is cheaper at this point, so it certainly has that going for it. Just don't expect any performance increase from it.

  From John Booty