I dont understand it bleh!

[Tab]

What is it with PCI Lock and AGP Lock. I see alot of people people saying that if you have a 400Mhz FSB for the Barton Cores you'll need a 1/6th Divider. Can someone explain this to me in newbie terms.

 

[Technonut]

Ripped from The Tech Report:

While the front side bus in Athlon XP systems runs at 133MHz, the PCI bus needs to run at 33MHz, and the AGP bus needs to run at 66MHz. The PCI bus takes its cue from the system bus, running at a fixed fraction of the system bus?in this case, one quarter. This is referred to as a 4:1 PCI divider, because for every four ticks of the front side bus clock, the PCI clock gets one. AGP then runs at a 2X multiple of the PCI bus.

Of course, if you try to run the front-side bus at 166MHz without changing the divider, you wind up with a PCI speed of 41.5MHz and an AGP speed of 83MHz. And then you're overclocking nearly everything, from the chipset to the RAM to the AGP and PCI interfaces to the processor itself. Doing it this way can deliver some performance improvements. However, you're running components out of spec, and while some components can take the added speed, others can't. This can lead to stability problems. The bottom line is, if AMD ever does come out with a 166MHz system bus, they won't do so with the PCI and AGP interfaces overclocked. Instead, they'll change the PCI divider to 5:1 to compensate for the bump in front side bus speed.

EDIT:

Read through the whole article linked above.... I hope this helped. The same principal would apply to truly run in spec at a 400MHz FSB.

 

[Tab]

I really dont understand bus speed and pci and agp speed. What do you get from locking it

 

[mechBgon]

The ability to increase the CPU/memory speed and performance without harmful drawbacks to the PCI equipment.

 

[ChampionAtTufshop]

Originally posted by: Tabb
I really dont understand bus speed and pci and agp speed. What do you get from locking it

ok at 100mhz frequency for cpu, there is a 1/3 divider in place for pci to keep the pci devices (ide controller, pci add in cards, usb, onboard nic, etc) in spec for their designated bus speed (33mhz)

for 133mhz frequency for cpu, there is a 1/4 divider
for 166mhz frequency for cpu, there is a 1/5 divider
for 200mhz frequency for cpu, there is a 1/6 divider

so if your cpu frequency was 165, pci bus would be WAY outta spec and some devices may not function either properly or at all.
when the cpu frequeny gets bumped to 166, all is well.

the newer nforce2 boards have a feature called agp bus locking. this enables the user to lock the agp bus at 66mhz (agp spec) which in turn locks the pci bus at 33 (agp divided by 2 equals pci).

the last few generations of p4 boards have always had a pci/agp lock.

**note the above explanation is taken into account before teh "ddr" portion for the cpu's**