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Advanced users

If your memory is faster so is your entire system

Many users are fortunate in having a BIOS which allows them to improve critical memory timings. Vendors are often over cautious when setting the defaults.

Your ability to change memory speed timings will depend on the Chipset and BIOS supplied with the motherboard in your computer.

Caution: You should write down all of your current BIOS settings.


One small change at a time, please

Make a record of changes as you proceed, so you will know exactly which alteration is worthwhile in your particular system.

Make only small changes and only one at a time, testing your system each time you make a change. If you encounter increased errors or a failed bootup, then access the BIOS on next bootup and change that setting back to the previous value.

The improvements you can make will depend on your BIOS type, and the computer components. You will need to consult your manual and/or visit the manufacturer's Web site to get the details that apply to your own BIOS type and version.

Record it - Change it - Test it

Remember: There is never a guarantee that a BIOS alteration will have the desired result. If, however, you have a record of the previous setting (one that works), you can easily enter the CMOS and enter the original value.

No permanent damage can occur, even if your computer should happen to stall.

You will probably have to use timing settings for the slower RAM, if you have mixed RAM modules in the memory banks.


Understanding main memory

Memory speed depends on two factors:
1 DRAM Speed/Technology - the speed rating, & quality, of the memory you purchase
2 Memory Timing Settings - your BIOS settings for that memory

DRAM Speed: This depends on the physical quality of the memory in your computer. It's the minimum access time that your DRAM can physically handle, and is rated in nanoseconds (e.g. 50ns) or, more recently in frequency (e.g. 100MHz). This sets a physical limit on how fast you can set the Memory Timing Setting for the memory in your computer.

Memory Timing Settings: Just having a memory module(s) on your motherboard is insufficient. The system must be told how to (best) manage that memory. The memory's real speed is determined by the timing that the system is told to use, usually via settings in the BIOS setup program (CMOS). These settings tell the system how quickly it can try to read/write to memory.

Memory Timing Settings are, basically, stated in CPU clock cycles (also called Wait States) - the more clock cycles allocated to an activity, then the more time it takes. Hence, the lower you can safely set the Timings, then the faster your memory will run (and your entire computer system).

It is quite possible your current Memory Timing Settings are set too high (memory running slower) because Auto Configuration, or a computer assembler, is too conservative as a protection against a possible occasional error in extreme circumstances. No gamer would find that acceptable!
Note: Some systems automatically set the memory timing based on the speed of the memory.

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Auto Configuration

The default Auto Configuration setting in the CMOS uses very conservative memory timings to ensure the PC will remain stable under ALL conditions. Many default settings can be safely altered.

First record all the current settings and then disable Auto Configuration.
You can't tweak your memory timings until it's disabled.

Memory timings are normally found in the

Advanced Chipset Setup

You should concentrate on the Timings first. These usually give the most dramatic speed improvement to your computer. The memory timing level you can specify depends a great deal on the kind of DRAM you are using. Read/writes usually occur in groups for 4 (saves time that way). The first of the four is much slower because initialization must occur (referred to as Latency). The next three are much faster (no Latency occurs) and are referred to as subsequent read/writes.

For example, in most Pentium systems, FPM (fast page mode) memory has a cycle time of 3 clock cycles for subsequent read/writes, EDO (extended data out) memory runs with only 2 clock cycles, and SDRAM memory usually requires only 1 clock cycle. Latency occurs with all of them.

A further factor involved in setting memory timings is the Motherboard's Chipset - some Chipsets allow faster timings than others.

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DRAM Read Timing (Bursts)

Set it lower, and test your system under computer stressful situations.

Memory reads stored data as specific memory DWords or bits. For greater efficiency (speed) these are read in sequential sets of 4, or 8 (normally identified as xyyy). The first read/write (the x) of the four must first be initialized and hence is much slower (latency) than the other three (y 'bursts'). Latency still occurs with modern 'fast' memory (manufacturers may tell you that SDRAM has a burst access of '1', and 'forget' about the latency - its really 5-1-1-1, a total of 8 clock cycles)

These will be presented by your BIOS in a format like 5222 or 7333 , or a combination of both 7222/7333. The 5222 should be read (by you) as four separate numbers e.g. 5, 2, 2, and 2. Each of these is the number of CPU clock cycles allocated to reading that DWord. The x portion, latency for the first read/write, is the DRAM Leadoff Timing (see next).

Obviously smaller numbers are faster (like changing x333 to x222). Unfortunately, your memory itself may not be fast enough to cope with the smaller time allocated and errors could result. You can see why some trial-and-error is required by each user. If your computer experiences errors, crashes, freezes or even refuses to boot, simply go back to a higher value.

Change 7444 to 7333
Change 7333 to 5333
Change 5222 to 5111

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DRAM Write Timing (Bursts)

Set it lower, and test your system under computer stressful situations
The same applies as DRAM Read Timing (note: the values are the same for FPM and EDO RAM)

DRAM Leadoff Timing

Set it lower (low values are only for fast RAM).

This one is the x in the above DRAM Read/Write Timing

The fastest settings have changed with faster Chipsets.

The 430 FX Chipset can read fastest in a burst with 7-y-y-y.

The 430 HX can use 5-y-y-y.

The latest Chipsets will use . . .

. . . consult your motherboard manual for details of your own Chipset.

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RAS to CAS Delay

Set it lower, and test your system (not all RAM modules can cope with a lowest setting).

This is the amount of time (number of CPU clock cycles) a CAS is performed after a RAS.

The terms CAS and RAS are widely used in memory timings. The memory structure used for 'read from', or 'write to', is divided into columns and rows. Hence, CAS stands for Column Access Strobe and RAS stands for Row Access Strobe

RAS Active Time

Set it higher for improved performance (?)

The is the amount of time a RAS can be kept open for multiple accesses.

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DRAM Speculative Leadoff

Enable it, for many Chipsets; monitor performance carefully.
It enables an earlier first access to memory.
The memory controller initiates the read request before the address for the read has been completely resolved. This results in a small performance increase but does not work with all systems.

Turn-Around Insertion

Leave it disabled
Enabling it inserts an extra clock cycle (longer wait state) between consecutive DRAM read cycles.
Back-to-back burst reads will normally occur without adding an extra delay. Disabled is usually OK.

System ROM Cacheable

Enable it, if you use BIOS RAM Shadowing.
BIOS RAM Shadowing copies its contents into main memory for improved performance (usually).
Enabling System ROM Cacheable will further improve the performance by caching this area.

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Increase memory speed by up to 30% with Interleaving

If you have a modern high quality memory module and a top of the range Motherboard, you may be able to increase RAM speed substantially. Micron's PC-133 has this ability, but most standard SDRAM 133MHz memory have not. Motherboards with the VIA Chipset (Abit) allow it, but many others do not.

Interleaving permits simultaneous access to 2 - 4 memory banks instead of the normal sequential access. Your memory access will not, of course, increase by 2 - 4 times because of Latency (see above), but the increase is substantial (perhaps 30%) and very worthwhile.

The CPU looks for required data in RAM when it fails to find it first in L1 cache, and then in L2 cache. Faster RAM means the CPU does not need to wait so often (idle times) for data to become available from RAM - and that means greater overall computer speed.

Look in your BIOS, or manual, for items like Force 4-Way Interleave (Enable it) and DRAM Bank Interleave (select 4-Way).

THPC has no experience with Interleaving and will not offer further advise. It is well worthwhile investigating if you have top quality RAM. You'll get full details of its enablement at the manufacturer's Web site, and you can visit for a comprehensive description of one user's (Moto) personal experience.

Feedback on Interleaving would be greatly appreciated.

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Your own BIOS may not have all of the above, or may use slightly different names for some. Also, your BIOS may have some other settings that apply to that Motherboard/Chipset.

Blind experimentation can be time-consuming, so investigate fully before making any changes.

Read the CMOS Help, or the BIOS help file, or look in your Motherboard manual. You can also get useful details on the manufacturer's Web site, and at the UserGroups.

Update the BIOS:

It is always advisable to look for a BIOS update at the manufacturer's Web site. It will be an improved version, may be faster, and may even give you greater accessibility to functions.

Flashing (updating) the BIOS is usually quite easy. Remember, however, that you computer will not boot without a working BIOS, so read the manufacturer's instructions very carefully before you get started. In particular, look for a method that will backup your BIOS to a floppy as a safety measure.

Many manufacturers provide some method, such as a batch file, to automate the flashing process for you - that makes life very easy indeed!.

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TweakBIOS Utility

Some BIOSes do not allow you to access the memory timings.

You can use a utility: TweakBIOS, or the difficult to use AmiSetup.

TweakBIOS works with a large number of different BIOSes and has some helpful comments.

A lower setting is nearly always faster, though you will still need to check each one.

You MUST first make a note of the original setting(s), even if using the TweakBIOS utility. You will not damage the operation of your system by changing a default setting PROVIDED you know the original. Returning to the original setting will then be very easy.

TweakBIOS (shareware)         TweakBIOS Home Site

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Please remember that you alone are responsible for the consequences of any changes you make to your computer hardware or software.

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