200 FSB w/ asynch 133 memory or 266 FSB w/ synch 133?

Zzzt

Member
Sep 8, 2000
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I'm almost embarassed to ask this.

I was recently asked by a customer what the difference between the 200 and 266 bus tbirds. Easily answered. He then asked about the Chaintech 7AIA. I told him that that board only suppots a 100MHz FSB, but will run 133(266) to memory. He then asked if the rest of the board runs slower. I replied that that wasn't the case because the PCI bus is still running at 33 and AGP is still running at 66.

If the bus to memory is 133(266)MHz wide, exactly what are we limiting when we have the cpu running at 100MHz at whatever multiplier??

I really hated to tell the guy that I didn't have a solid answer for him. I guess I gained a bit of respect in his eyes, but I still didn't like having to say,"Idunno."
 

Sunner

Elite Member
Oct 9, 1999
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You're losing bandwidth mostly.

And you'll see a performance drop from the asynch bus.
But its not THAT big a deal unless you're c performance fanatic.
 

Guilty

Senior member
Nov 25, 2000
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FSB+PCI just isnt as wide as a true 133 bus. The memory may be running at 133MHz but a true 133MHz system will outperform it, look at the KT133/KT133A, you gain some memory bandwidth and multimedia bandwidth. The average consumer wont notice though.
 

Zzzt

Member
Sep 8, 2000
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The problem comes when you figure that if the memory is running at 133MHz, then that must mean that the CPU to memory bus is sending chunks of data at a rate of 133 MHZ. So if the cpu to memory bus is running at 133MHz, what the heck does the 100MHz refer to? From the CPU to what?

Maybe the CPU is talking to the northbridge at 100MHZ, and the northbridge is talking to memory at 133, but if that is the case, the northbridge-memory speed gets bottlenecked by the cpu-northbridge down to 100MHz, which should make a zero difference between running the memory at 100 or 133, but we see a difference, so that can't be quite right...

Idunno.
 

Brian23

Banned
Dec 28, 1999
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With the B version of the tbirds (200MHz FSB) they talk to the Northbridge at 100MHz DDR = 200MHz, and the Northbridge talks to the PC133 memory at either 100MHz or 133MHz. The board gets the 100MHz from the FSB speed, and the 133MHz comes from the FSB (100) + PCI (33). The Althlon advertises that it has a 200MHz FSB, but it really is 100MHz DDR. As for the C version of the Athlon (266MHz) it has a DDR FSB to the northbridge also. Then the Northbridge talks to the memory at the FSB speed (133MHz).