TechSpot

Is it safe to change Memory Latencies??

By franklogus
Aug 1, 2004
  1. Hi all !
    I just got my new PC, with the basic following spec:

    Processor: Pentium 4 3.0C (HT, 800Mhz, L2=512Kb)
    Mobo: Asus P4P800-E DeLuxe
    Video Card: MSI 9800PRO
    Memory: 02 sticks of 512 MB Samsung DDR400 (The Model of my memory is recommended for Asus for Stable Overclock with my MoBo )
    HD : SATA 150, 200 GB, Seagate

    I am very glad with my computer (except by bad noise of stock cooler of my CPU), but I would like to give some "boost" on it. For to do it, I can use some features of my MoBo, but I am afraid of to do something wrong, because I am not an PC expert (far from this ...).

    I have read some reviews, and the most interesting I found at this site: X-bit Labs, where they did a nice and deep analysis of my MoBo...

    They told that there is a feature in the BIOS where we can get some "boost" of performance, but we need to have some pre-conditions to get success: "... you can achieve better results with DDR400 SDRAM, but only if you also enable the Performance Mode, but you need support of 2-2-2-5 timings for that! Not all memory modules are operational at such timings..."
    "... Performance Mode gives a positive effect only with 200MHz FSB and requires that the memory modules were stable with 2-2-2-5 timings at such FSB clock rate. By setting the Performance Mode option to “Turbo”, you reach noticeable performance gains..."

    So, my question is:

    1) Can I to change these settings of my current memory in a safe way?

    2) Is there some danger of damage on trying it?
    I use the CPU-Z utilitary, and it says me that my memory have the settings : 2,5 - 3 - 3 - 8... Can I try to change it (into BIOS) to 2 - 2 - 2 - 5, without any additional change? [Only to remember, my memory is "approved" for Asus to support overclock].

    3) Why doesnt my Samsung Model Memory (approved by Asus) dont have that settings (2-2-2-5) originally??

    As an additional information, I tried to enable the function TURBO without to change the memory settings, and the system "hanged"... So, I think I need to change it (if there is technical possibility, of course..), to get success about it ...

    Well, that's it ... Thanks a lot for any help !!!
     
  2. BrownPaper

    BrownPaper TS Rookie Posts: 467

    The lowest you should lower your memory latency to in the Bios are the rated latencies on your ram. The rated latencies for your ram should be on a sticker on your ram sticks or with the package of the ram.

    If your ram is rated to do 3-4-8-8, setting anything more agressive in the Bios (e.g. 2-2-2-5) will cause your system to hang, have Bios error beeps, or have a bunch of memory errors in a memory testing program like MemTest86. Having memory errors will probably trash your OS and the data on your hard drive.

    Just set the latencies in the Bios to the lowest settings your memory will support. If you still have problems, relax the latencies a little.

    Btw not all ram will be stable with the Turbo feature of boards such as Asus, Abit, etc. The ram that can do 2-2-2-5 latencies are really expensive.
     
  3. Nic

    Nic TechSpot Paladin Posts: 1,928

    I am running my TwinMOS PC3200 (2.5, 3, 3, 8) 256MB DDR sticks at 2, 2, 2, 5 timings, but I chose those particular modules because I knew they were good for those speeds.

    You could try gradually tuning your sticks one step at a time, seeing if your PC still boots, test for errors using Prime95, then increasing things a little more, and repeat. Undo the last change when you start to detect errors. You can also try increasing the voltage to your memory modules. Be careful as you could permanantly cook your memory, then you'll need to replace any modules should the worst happen. I doubt you'll notice much improvement in performance with tighter timings, as this is not something that P4s tend to care much about. Still, if you want to give it a go ...
     
  4. franklogus

    franklogus TS Rookie Topic Starter Posts: 64

    Thanks a lot for your hints, buddies !
    I have run the program AIDA32, and, there, it "tells" that my memory have maximum CAS latency of 2.5 (5.0 ns @ 200 mhz)... Would be this a limit (in other words, wont I be able to change the latency to "2") ??
    Thanks a lot for any additional information !!
     
  5. Nic

    Nic TechSpot Paladin Posts: 1,928

    Try it and see ...
     
  6. Bug

    Bug TS Rookie Posts: 180

    The manufacturer of the memory will typically test the memory for its timing performance and will then mark it for a slightly lower setting. For example, if the memory almost hits 2-3-3-5 but is not fully stable, they will then test it at 2.5-3-3-5 and if it is stable, then they stamp it. They will test a certain number of these modules and all from that batch will get the same stamp. Even though some modules may be able to be set at a better latency. They may not adjust voltage or any of the other time settings to see if it will clock lower. You may be able to play with these numbers. On a memory stick, there are a number of memory modules. The stick is only as good as its weakest module.

    The only way to see what the memory module is capable of is to test it. change it. test it. change it. test it...
    Start with the 2.5 - 3 - 3 - 8 and lower it to 2-3-3-8
    if this works, try and lower another one
    if not, you can try to increase the voltage to provide additional stability, but this is where you can fry the ram
    Very rarely will you get a 2.5-3-3-8 to 2-2-2-5 as the memory is not high enough quality. Rather, look for memory that is rated closer or is rated specifically for those settings. This memory will be expensive.

    When they state that the memory is good for OCing, they are more than likely talking about the memory clock speed. You are running 400MHz DDR. They are talking about bumping that up. If you want to OC this speed, increase it very slowly and benchmark it to verify stability. If you start to see errors, clock it down and you have found your stable OC speed for the system.

    Bug
     
  7. Trunks

    Trunks TS Rookie

    Hi I have almost the same setup as you:

    Processor: Pentium 4 3.4 (HT, 800Mhz, L2=1MB Prescott 478)
    Mobo: Asus P4C800-E Deluxe
    Video Card: BFG FX5900XT OC
    Memory: 04 sticks of 512 MB Kingston DDR400 (KHX3200ULK2 timing 2-2-2-5)
    HD : SATA 150, 300 GB, Seagate

    My system is stable with the timings of 2-2-2-5 with the 2GB of RAM running Dual channel but I cant figure out how to enable performance mode. Any Ideas? Also you can get a gig kit of the KHX3200ULK2 memory for 223 bucks from zipzoomfly.com, kingston did tell me that the 875P chipset doesnt like the 2-2-2-5 timings and causes it to hang/crash but it seems to work like a charm in the P4C800-E Deluxe board.
     

    Attached Files:

  8. Trunks

    Trunks TS Rookie

    I messed around with my bios settings some more and in the CPU settings there is "Performance Accel. Mode" the settings are -Auto -Standard -Turbo. I had it set on Turbo and thats what gave the result of my actual RAM timings of 2-2-2-5 with Performance Mode in CPU-Z disabled (PAT). When I set the BIOS setting to AUTO, it enabled the performance mode but lowered one of my timings to 2.5-2-2-5, this is still extremely low compared to most memory modules and stable for my ssytem.
     

    Attached Files:

  9. LeeHunton

    LeeHunton TS Rookie

    ok i stumbled on this article and i thought, YES just what i needed to find.
    ok heres my situation.
    i saw what u put about performance mode.
    my RAM i bought was £110 and its corsair DDR400 latencys 2-2-2-5 and freq 200MHZ (400MHZ effective) PC3200.
    I have a ASUS P4C800-E Deluxe, on CPU-Z it showed my latencys to be 3-3-3-8, and a freq of 177.7 MHZ which both are wrong , 2-2-2-5 is what it should be and also 200MHZ not 177.7.
    then i read ur performance mode thing and i enabled it and now there 2.5-3-3-6 and freq is still 177.7. The latencys and freq are stil both wrong, and i dont know what to do to get them to what they should be, they should be 2-2-2-5 and 200MHZ freq.
    i paid a lot for my RAM and i want it to be at its best. i didnt pay for less performance of what it said on the box.
    can any of you help me with this please.
     
  10. pkroks

    pkroks TS Rookie Posts: 376

    i not too technical about this stuff. can someone explain ram timings to me? :)
     
  11. etherga

    etherga TS Rookie Posts: 69

    Didnt see wher esomeone added thsi already but if you do, and you probably will, slim up your timings to a point where they're unstable and your comp wont boot, you'll have to remove the motherboard battery to reset BIOS settings.
     
     
  12. Blakhart

    Blakhart TS Rookie Posts: 510

    First off, think of ram as a big spread sheet, with the timings relating to how fast (in cpu cycles) a certain column and row (the intersection of wich is a memory address) can be accessed by the memory controller.

    There are rules that apply to memory timings, and this link sums them up nicely:
    http://www.mushkin.com/doc/techSupport/papers/latency.asp
    The above is the single best piece of info I have found on memory.
    Pay attention to this quote:

    " The exact same is true for tRAS short for the RAS Pulse width. Historically, tRAS was defined as the time needed to establish the necessary potential between a bitline pair within the memory array until it was safe to write back the data to the memory cells of origin after a (destructive) read. Pay attention to the word read here.
    Memory, in many ways is like a book, you can only read after opening a book to a certain page and paragraph within that particular page. The RAS Pulse Width is the time until a page can be closed again. Therefore, just by definition, the minimum tRAS must be the RAS-to-CAS delay plus the read latency (CAS delay). That is fine for FPM and EDO memory with their single word data transfers. With SDRAM, memory controllers started to output a chain of four consecutive quadwords on every access. With DDR, that number has increased to eight quadwords that effectively are two consecutive bursts of four.

    Now imagine someone closes the book you are reading from in the middle of a sentence. Right in your face! And does it over and again. This is what happens if tRAS is set too short. So here is the really simple calculation: The second burst of four has at least to be initiated and prefetched into the output buffers (like you get a glimpse at the headline in a book) before you can close the page without losing all information. That means that the minimum tRAS would be tRCD+CAS latency + 2 cycles (to output the first burst of four and make way for the second burst in the output buffers).

    Any tRAS setting lower tRCD + CAS + 2 cycles will allow the memory controller to close the page “in your face!” over and again and that will cause a performance hit because of a truncated transfer that needs to be repeated. Along with those hassles comes the self-explanatory risk for data corruption. That one is not a real problem as long as the system is kept running but in case it is shut down and the memory content is written back to the hard disk drive, the consequences can be catastrophic. For the drive, that is."

    What they're saying is going from 6/2/2/2 to 5/2/2/2 pretty much gaurantees eventual data loss.
    Going lower than a tRAS of 6 in this case means trouble. Add the CAS to tRCD (RAS-to-CAS delay), plus 2 cycles to get the most reliable tRAS for your system.
    Use memtest86 (or similar) to verify your settings are stable, allowing a few complete passes error free before you call it good.

    Word.
     
  13. LeeHunton

    LeeHunton TS Rookie

    i still could use some help, i already know about how RAM works, but my situation explained above has got even worse.
    now my timings are 3-4-4-8 (way above the 2-2-2-5 which is what it should be doing) and the freq is now a shocking 160Mhz, even lower than 177.7. (there like that even with performance mode enabled)
    i did overclock my processor just after i posted my last reply, a little further up, minght that be why they got worse. but why did they get worse and how to i fix them both to 2-2-2-5 and 200MHZ freq, which is what they should be.
    help plz.
    (if nothing else works i will change the timings but if i do try then how to i do it, i have a ASUS p4C800-E deluxe, tips would be nice, o and MY RAM DOES SAY THAT IT SHOULD BE 2-2-2-5, just incase any of u were wondering, and 200 MH freq.)
     
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