Does PC133 memory actually run 133 Mhz, if the FSB is only 100 Mhz ?

Qzruh

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Sep 19, 2000
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Some people around me said that the memory clock should be the same as the FSB, since it is a Syncronous DRAM, so that the PC133 memory paired with processor which have 100 Mhz FSB, only run at 100 Mhz.

I dont think this way, but i am lack of knowledge of this, i have read (sometimes ago, i forgot) in anandtech or tomshardware, they said that the PC133 run in 133 Mhz in the motherboard that have the chipset supporting 133 Mhz memory clock. So i think the chipset is envolved in this case..

I will give an example, i have a T-Bird 700 which have 100Mhz FSB, with PC133 memory. Some people telling me that my PC133 memory will not run in 133Mhz frequency, since my processor FSB is only 100 Mhz. I dont think this statement is correct, because i know that my chipset, VIA, is supporting 133Mhz memory clock. So i ask anyone *please* who can explain me technically what is the relationship between FSB clock ,memory clock, and this VIA133 chipset, how come the 100Mhz FSB can accept the data from an SDRAM with 133Mhz memory clock, since the memory is syncronous.

Anyone can explain me ? pleasee.....
 
Feb 24, 2001
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humm, it should be a ratio to the fsb. on my asus k7v it's 3:3 for pc100 and 4:3 for pc133. shouldnt be dependant on the speed (on most boards i would think). otherwise pc133 ram would just now be working with the thunderbird c chips. if i understand what you are saying.
 

Krioni

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Feb 4, 2000
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Well, to put it simply, the VIA chipset allows your memory to run Asynchronously in relation to the FSB of your processor.

In the BIOS of your motherboard there is a setting that allows you to run the memory at 1 of 3 options
1. FSB speed (100MHz)
2. FSB speed + PCI bus speed (133MHz)
3. FSB speed - PCI bus speed (66MHz)

This is really a very smart way that VIA has used to allow people to upgrade to there motherboards without having to buy new RAM if they have older PC66 memory, and for people who have newer memory (PC133) to take advantage of that even though the processor does not support that high of a FSB.

And, the RAM being "Synchronous DRAM" has to do with the RAM itself and is completely independent of the processor or motherboard (other than they have to support it :) .


 

Qzruh

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Sep 19, 2000
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Thx alot Krioni, i got your point.
So this is because the chipset allow the memory to have clock asyncronously with the FSB.

one more question,
Will the frequency difference will maka e bottlenck ? imho, if the 133 Mhz memory feed the data to a 100 mhz processor ?

Thx

Andy

btw, where can i find an article of this subject on the internet ?
 

14k

Senior member
Mar 5, 2001
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so if i had an athlon t-bird 1.2 (266) and a motherboard which had a 266FSB what RAM would I use because SDRAM does not come in PC266?.. or will i get PC133 RAM and the ram will run at 133mhz because the motherboard's fsb supports anything upto 266mhz?
 

sitka

Senior member
Dec 29, 2000
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Athlon C means an "effective" 266FSB it is actually operating at 133MHZ but just doubles the amount of things it can do at 133. Same with Motherboard and claims of 266. It is running at 133. So sdram at 133 matches nicely with 266 or 133. DDRAM also has a base frequency of 133 but uses the "effective" 266 speed that matches the newer Athlons. Just think of it in terms of efficiency. Things labled 266 are just twice as efficent as things labled 133. If something is capable of this higher efficency, whoever built it is sure to tell you about it. DDRAM is PC266.