The BIOS (Basic Input/Output System)

The BIOS Memory Timing

IntroductionSetting RecommendationsSpecial Note for MR BIOSBack to computer news

Introduction

The performance of the mainboard is highly depending on the memory timing you adjust in your BIOS setup. The settings you are able to change and the different values however differ a whole lot from chipset to chipset and from BIOS to BIOS. Some BIOSes hardly leave it up to you to tune up your system, others give you almost too many settings to choose from and some BIOSes adjust the memory timing very well after you only had to choose the DRAM speed. In general you can say that for optimal performance you should keep most of the values as low as possible. Should you choose them too low however you will either occur system crashes/hangs or your system wont boot at all. Even if this should happen there's nothing you'll have to fear though. Just load and you can be sure your system will work just fine - setup defaults after entering setup again just not too fast however. Also there's no long term damage to fear - readjust your settings and everything will be as it was before.

I will not discuss the basics about the BIOS, because there already exists an excellent and extremely comprehensive summary, the BIOS Survival Guide, latest edition 5.1, which is a must read for everybody who isn't already quite experienced with the BIOS setup. If you want to, you can download the whole Guide as a Word document and read it relaxed offline. All the topics discussed in this Guide I wont even touch!

The Settings

You'll find the memory timing settings usually in the Advanced Chipset Setup section of the BIOS setup.

• Auto Configuration
  • If you ever should want to get the most out of your system then switch this one off - quickly ! You anyway wont be able to change anything unless you do.
• DRAM Read Timing
  • Short Explanation:
    Most accesses of the main memory are actually happening as a Burst. This is due to the cache not fetching only one DWord/Word/Byte, but rather than that fetching 4 or 8 consecutive DWords in a line. That's obviously much more effective than getting each byte on its own into the cache or the CPU. A burst read is done (in easy words) by telling the memory the first address first and then consecutive DWords can be read in a row, without telling the memory each address anymore. This obviously saves time. In clock cycles this looks then like x-y-y-y for a normal burst or x-y-y-y-z-y-y-y for a so called back-to-back burst. For Pipelined Burst Cache RAM e.g. this is 3-1-1-1 or 3-1-1-1-1-1-1-1. That's the amount of clock cycles the CPU needs for reading from its PB cache. Now for the main memory it's not a fixed value like for the PB cache, instead you can and have to adjust the x,y and sometimes also the z, due to the different DRAM types and speeds.
    Now after you've read this and hopefully understood it as well ;-), you see that the system will be faster when the x,y,z values are low rather than high, 'cause it takes the CPU less clock cycles to actually get the data it wants to process.
    The DRAM Read Timing is more or less the 'y'. Therefore you normally can choose from something like x222 and x333 for EDO (which is faster) and x333 and x444 for FPM RAM. You often have to choose it combined which each other, like x222/x333 and x333/x444, where the higher value stands for FPM, the lower for EDO RAM.
  • Recommendation:
    Choose the lowest possible value and try out your system ! If you don't occur crashes after starting some programs (best under Windows 95 or more sophisticated OSes) it obviously is the right setting for your RAM.
• DRAM Write Timing
  • Short Explanation:
    Well, it's the same as the read timing, with the difference that the values are the same for FPM and EDO RAM, if you shouldn't have known, EDO is only faster being read as FPM, the write accesses are the same.
    So also, you adjust the 'y', this time for the read timing.
  • Recommendation:
    As above, as low as possible. Change it and check your system !
• RAS to CAS Delay
  • Short Explanation:
    This is the amount of clock cycles it shall take for the Column Access Strobe to follow the Row Access Strobe. Chinese for you ? Sorry, I really can't explain this computer basic knowledge to you, it would burst the dimensions of my whole site ! There's some info about that in the BIOS Survival Guide, memory section, please look it up there.
  • Recommendation:
    Again as low as possible, but again remember that not every RAM module is able to work with the lowest setting, so test your system after changing it !
• DRAM Leadoff Timing
  • Short Explanation:
    This one is the 'x' of the above described burst read/write. Here are some interesting differences between the Intel Triton FX and HX chipset. The FX can read fastest in a burst with 7-y-y-y, the HX is able to do 5-y-y-y - that's the reason why it's faster !
    Writing in the FX is actually always done in a 5-y-y-y, the HX is also able to do a 4-y-y-y, but Intel recommends this only for 50 or 60 MHz bus clock.
  • Recommendation:
    And again keep it as low as possible. The value '5' for the HX chipset is mainly meant to only work well with 50ns or faster EDO.
• Turbo Read Leadoff
  • Short Explanation:
    Well, that seems to be a quite stupid name for choosing the lowest Leadoff setting, most likely '5' for HX boards. Still don't know what turbo chargers have to do with computers...
  • Recommendation:
    Enabled of course, but as above be aware of ....
• Turbo Read Pipelining
  • Short Explanation:
    I haven't got a clue what that's supposed to mean ! Maybe somebody will enlighten me.
  • Recommendation:
    Well, it sounds turbo-good to me, enable it and see how it goes !
• Speculative Lead Off
  • Short Explanation:
    The 430HX chipset is capable of allowing a DRAM read request to be generated slightly before the address has been fully decoded. This can reduce read latencies.
    More simply, the CPU will issue a read request and included in this request is the place (address) in memory where the desired data is to be found. This request is received by the DRAM controller. When enabled, the controller will issue the read command slightly before it has finished determining the address.
    Thanks to Novations Technologies Inc., who gave me this info.
  • Recommendation:
    BY ALL MEANS enable it TO GAIN PERFORMANCE

OK, so far the settings I know, which are NOT discussed in the BIOS Survival Guide. If you should have settings I shouldn't have discussed here yet and which you also couldn't find in the Guide, then

Special Note for MR BIOS Users

MR BIOS usually only lets you choose the DRAM speed, like 70ns/60ns/50ns, but it's well known for it's aggressive timing. So if you choose 50ns, you should have performance wise the best configuration --- as long as it works.

Flash BIOS upgrades
Wim Bervoets' excellent guide to Flash BIOS upgrades for all M/B manufacturers present on the web ! Not to be missed !

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