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/5 PCI Divisor? What is this bois update you people speak of?
- Thread starter Ferg
- Start date
- Joined
- Apr 10, 2001
To explain:
On current motherboards the highest PCI Divisor today is 4. If you rev your FSB up to 133Mhz then you're system (if a recent board) kicks the PCI divisor up to 4. 133/4 = 33mhz. 33mhz is what all you PCI and HDD devices are designed to run at. This means going above 133FSB puts stability as questionable. A lot of PCI divices don't even like being overclocked by 2 mhz. This limits the FSB you can use.
Add a PCI divisor of 5, and your new limitation becomes your memory. With a PCI divisor of 5, you can run a FSB of 165mhz and keep your PCI cards and peripherals at default speed.
I'm sure you can see the value here.
- Thread Starter
- #3
I wrote quite article on this matter about a week back, since i cant seem to get the proper link to that thread i will just post it here.
Well at first glance it should be an obivous answer, configuration B, but I am not so sure that there is that much of a difference. Because, when you run a system at 133 Mhz the PCI bus automatically changes to 1/4 of the the front side bus which would equal to 33 Mhz. When it is at 100 Mhz then it runs at 1/3 of the front side bus which is alco equal to 33 Mhz. So If all of the components in your computer are remaining at the same speed then what are we gaining by increasing the front side bus. Well as far as I know the only difference is that the ram. In a 100 Mhz fsb motherboard the ram can be set to equal the front side bus + the pci bus speed. In an unoverclocked system that would be 133 Mhz. That is the same speed that the ram runs at in a 133 Mhz speed except that since it is running at the same speed as the fsb no bottlenecks occur. On the otherhand by having a system running at a speed of 133 Mhz it would take increasements of 4 Mhz for every 1 Mhz in PCI bus speed increase. Therefore assuming that a 133 Mhz system and a 100 Mhz system could both overclock over their default values at equal amounts then the PCI bus would be faster on the 100 Mhz system. Example. If you ran a 100 Mhz system at 112 Mhz then the PCI bus would be 37 Mhz. If you ran a 133 Mhz system at 145 Mhz then the PCI bus would be at 36 Mhz. While this is not a very large difference in speed it is some. So lets recap. In a 133 Mhz system the advantage is less bottlenecks in memory. The disadvantage is slightly less PCI bus speed. And vis-versa is true for a 100 Mhz system. So who is the winner. Well I believe the advantage goes to the 133 Mhz for two reasons. The first is the added memory speeds out weighs the slight disadvante in PCI bus speeds and Most 133 Mhz chipsets can overclock better than 100 Mhz chipsets. The VIA KT133 and VIA KT133A chipsets for example. Most KT133's max out at around 112 while I believe that most KT133A chipsets can do around 150, but I am not sure about that. So my conclusion is that while the 133 Mhz front side bus speeds are better than the 100 Mhz front side bus speeds there is not as much difference as you would think. Does Anyone have a link to benchmarks of identical systems except one having a VIA KT133 chipset and the other having a VIA KT133A chipset? This would show the real difference.
So by changing the divisor to 5 i think performance increase wont be as much as it could be. Although 165 Mhz memory is very impressive.
Well at first glance it should be an obivous answer, configuration B, but I am not so sure that there is that much of a difference. Because, when you run a system at 133 Mhz the PCI bus automatically changes to 1/4 of the the front side bus which would equal to 33 Mhz. When it is at 100 Mhz then it runs at 1/3 of the front side bus which is alco equal to 33 Mhz. So If all of the components in your computer are remaining at the same speed then what are we gaining by increasing the front side bus. Well as far as I know the only difference is that the ram. In a 100 Mhz fsb motherboard the ram can be set to equal the front side bus + the pci bus speed. In an unoverclocked system that would be 133 Mhz. That is the same speed that the ram runs at in a 133 Mhz speed except that since it is running at the same speed as the fsb no bottlenecks occur. On the otherhand by having a system running at a speed of 133 Mhz it would take increasements of 4 Mhz for every 1 Mhz in PCI bus speed increase. Therefore assuming that a 133 Mhz system and a 100 Mhz system could both overclock over their default values at equal amounts then the PCI bus would be faster on the 100 Mhz system. Example. If you ran a 100 Mhz system at 112 Mhz then the PCI bus would be 37 Mhz. If you ran a 133 Mhz system at 145 Mhz then the PCI bus would be at 36 Mhz. While this is not a very large difference in speed it is some. So lets recap. In a 133 Mhz system the advantage is less bottlenecks in memory. The disadvantage is slightly less PCI bus speed. And vis-versa is true for a 100 Mhz system. So who is the winner. Well I believe the advantage goes to the 133 Mhz for two reasons. The first is the added memory speeds out weighs the slight disadvante in PCI bus speeds and Most 133 Mhz chipsets can overclock better than 100 Mhz chipsets. The VIA KT133 and VIA KT133A chipsets for example. Most KT133's max out at around 112 while I believe that most KT133A chipsets can do around 150, but I am not sure about that. So my conclusion is that while the 133 Mhz front side bus speeds are better than the 100 Mhz front side bus speeds there is not as much difference as you would think. Does Anyone have a link to benchmarks of identical systems except one having a VIA KT133 chipset and the other having a VIA KT133A chipset? This would show the real difference.
So by changing the divisor to 5 i think performance increase wont be as much as it could be. Although 165 Mhz memory is very impressive.
- Joined
- Jul 9, 2001
- Location
- WI
With the 1/5 divison you could run the PCI in spec at 166.66. Gee, don't they sell PC166 memory? How convienent.
- Thread Starter
- #5
I know the sell PC166 memory, but two things. First of all that Epox motherboard does not work with PC-166 memory. It uses PC-2100 and PC-2400 memory. PC-2400 probably could make it. I didnt say that it would make it slower, i just said that until we increase the speed of our pci cards we are not going to see the results that we could.
