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Synchronize vs. non-synchronize FSB/Memory speed?

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Old March 11th 04, 08:11 AM
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Default Synchronize vs. non-synchronize FSB/Memory speed?


I've seen numerous posts indicating that it's best to synchronize the CPU
FSB and memory bus speeds (i.e., 1:1 ratio), and I've been "experimenting"
and have some questions that I hope that you all can help with. This
experimentation is mainly for educational purposes (my own), so please don't
criticize the equipment ...

Ok, what I have is:

Motherboard: Asus A7V8X-X
CPU: Duron 850
Memory: PC2700 (1 stick, 512MB)

As I understand things, the Duron 850 CPU has a CPU clock of 100 MHz, and an
FSB of 200 MHz, and the relationship of CPU, (KT400) chipset/memory
controller, and memory is something like:

CPU ------------ KT400 -------------- Memory
FSB Memory Bus

I gather that a "1:1 ratio" or "synchronized" means that the FSB speed is
equal to the Memory Bus speed, and that the reason that this is "good" is
that since the bus speeds on both sides of the KT400 are the same, no
buffering is needed in the KT400.

Is this correct?

Assuming that it is, the A7V8X-X BIOS has the following setting

- Multiplier
- External Frequency
- Memory Speed

"External Frequency" is shown as, for example, "100/33", and I think that
the "100" is the CPU clock speed (so it's equal to FSB/2) and the "33" is
the PCI bus speed.

Following the diagram above, I am guessing that the "Memory Speed" is the
speed of the memory bus (i.e., between the KT400 and the memory).

Is this correct?

With the setup that I have (described above), when I boot the machine and go
into BIOS, the default settings a

Multiplier: 850
Ext. Freq.: 100/33
Memory Speed: Auto

The system wouldn't boot pass the BIOS with these default settings, but I
was finally able to get it to boot into Windows XP by setting Memory Speed
to "266". With this setting the system seems to run stably.

Given the above (Ext. Freq.=100/33 and Memory Speed=266), isn't this NOT
synchronized (since FSB= 2 x Ext. Freq. = 200, while Memory Speed = 266)?

Should this work (it does!)?

Ok, now, due to what appear to me to be a somewhat buggy BIOS, the BIOS
doesn't seem to "normally" offer "200" as a selection for the Memory Speed
(it only offers 266, 333, and "Auto").

After much mucking around (a really LONG story), I was delighted to finally
be able to get "200" to appear as a selection for Memory Speed.

I thought that when I got to that point, "Great, now I can get the FSB and
Memory Speed synchronized.". BUT, to my utter amazement, when I set Memory
Speed to "200", the system wouldn't boot at all. I just got a black screen,
with not even the initial BIOS display. I had to power the system down,
then up, which with the A7V8X-X, causes BIOS setup to come back up
("Crashproof BIOS").

So now, I'm very confused:

- The system seems to run fine when the FSB and Memory Speed are NOT
- The system seems to NOT be able to boot when the FSB and Memory Speed are

Can anyone explain this?



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