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PC66 SDRAM VS PC100 SDRAM

Posted on 2000-02-28
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Last Modified: 2013-11-10
i HAVE A LX CHIPSET MOTHERBOARD with 64mb of SDRAM. I think it is the PC66 variety. My MB can be clocked up to 80 something Mhz.
Would it hurt the motherboard or existing memory if I bought PC100 memory  and ran it with my PC66 memory?
I would probably still run the MB at 66mhz.
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Question by:prae
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frache earned 50 total points
ID: 2564361

No problem ...
You can use PC100 ram.
You can mix PC66 and PC100 ram.

Note : Ok, also with PC133 ram ...
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by:jhance
ID: 2564556
>You can mix PC66 and PC100 ram.

Not a true statement.

You can mix PC66 and PC100 RAM as long as you run the memory bus at the speed of the SLOWEST RAM installed in the system.
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by:boom23
ID: 2564562
But if you overclock at 80 something mhz, then you might have a problem coz one of your ram is pc66 mhz.
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by:frache
ID: 2564719

More details :

-You can mix PC66 and PC100 ram if you still run the MB at 66mhz.

- 80 Mhz :
Make a try with PC100ram only, because you can have problem with processor or graphic card (-> PCI bus overclocked at 40 Mhz - 80/2 )
After, if everything is Ok ( test everything during 2 hours) , plug PC66 ram.
If you have problem, you can try to adjust ram parameters in bios.
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by:jhance
ID: 2564747
>- 80 Mhz :

>Make a try with PC100ram only, because
>you can have problem with processor or
>graphic card (-> PCI bus overclocked
>at 40 Mhz - 80/2 )


Again, you're confused.  On all motherboards the PCI bus clock is INDEPENDENT of the CPU and memory bus clock.

Where are you getting your misinformation?
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by:frache
ID: 2565348
WRONG :
"On -ALL- motherboards the PCI bus clock is INDEPENDENT of the CPU and memory bus clock".


Not agree with "ALL" ...

Many motherboard have PCI clock and AGP
clock synchronized with FSB clock (external processor clock). Particularly old motherboard with LX chipset ...
 
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by:sorgie
ID: 2565732
your not going to get any benefit from Pc 100 running at 66mhz and I really thing that trying the overclocking route with PC100 will if anything show no improvement and maybe just problems

stick with what your MB is designed for and save the extra expense.

Good Luck
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by:1cell
ID: 2565767
yes, the only benefit from running 100MHz RAM on a 66MHz bus is future upgradability.  Yes, it will work, but your 100MHz RAM will run at 66MHz.
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by:prae
ID: 2566347
One of the reasons I asked is that PC66 SDRAM is harder to find and MORE expensive than PC100 SDRAM in New Zealand. I can also get a good deal on PC100.  :-)
I'm not one for overclocking but could try as I heard that some PC66 can run at faster speeds. I have a couple of settings before I get to the 80mhz bus speed.
But thats where I get confused. Is the bus speed linked to the memory speed?
I thought the bus speed and memory speed were linked.
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by:frache
ID: 2568116

- Memory speed is linked with FSB - Front side bus = External processor clock.

-> With FSB at 66Mhz, you can use PC66,PC100 or why not PC133 ram.
-> With FSB at 80 Mhz ,PC100 is ok, but you can have problem with PC66.
Sometimes nothing to do ( "good" PC66 support 80 Mhz ).
Sometimes you can "play" with Ram timings in bios.

- Cache memory (level 2 or 3) speed is linked with FSB.

- AGP and PCI bus :  

With Pentium and first generation( LX chipset)  of Pentium II motherboards, often AGP speed = FSB, and PCI speed = FSB /2.

With second generation of Pentium II motherboard  ( BX chipset ) , 2 ways :

synchronized : AGP speed = FSB, and PCI speed = FSB /2.

asynchronized : whatever FSB speed, AGP speed = 66 Mhz / PCI speed = 33 Mhz.

Sometimes a motherboard have a jumper or a bios setting to change this parameter ( synchronized / asynchronized)

Synchronized is generally better for performance ( no lose cycles ).

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