64 bit and ram question

[stylezeca]

is there a northbridge on the motherboards for the 64bit cpu still? and do you have to have a certain type of memory for the 64bit and how does dual channel work exactlY? thanks/!

 

[Ryoga]

There's no northbridge in the traditional sense. To my knowledge there's now one single chip with the combined functions of the north- and southbridge functions (less the memory controller). Take a look at this reference design.

As for requiring a different type of memory... it's complicated. As best I can tell, the socket 940 CPUs required registered DIMMs, but the 754's didn't... but I'm not sure on this one since I haven't been following AMD recently. I'm fairly certain that the 939's don't.

Dual channel is pretty easy. Normally, there's one bus from the memory controller to the RAM, no matter how many banks of RAM there are. In dual channel, there's two busses. So while the clock speed for the memory bus for PC3200 RAM is only 200 MHz, it has an effective data rate of 800 MHz (200 * 2 DDR * 2 dual chanel).

 

[Matthias99]

As for requiring a different type of memory... it's complicated. As best I can tell, the socket 940 CPUs required registered DIMMs, but the 754's didn't... but I'm not sure on this one since I haven't been following AMD recently. I'm fairly certain that the 939's don't.

This is correct.

 

[sunase]

Originally posted by: Ryoga
In dual channel, there's two busses. So while the clock speed for the memory bus for PC3200 RAM is only 200 MHz, it has an effective data rate of 800 MHz (200 * 2 DDR * 2 dual chanel).

Your numbers are wrong. The 3200 comes from running at 200MHz, transferring data twice each clock (DDR), and transferring 8 bytes (SDRAM has a 64-bit wide data bus) each transfer. So the 3200 is arrived at by 200*2*8.

If you add a second channel (which requires a second stick of memory to be accessed independently at the same speed via the second channel) you then multiply by two again giving 6.4 GB/s total memory bandwidth for using both channels (note an individual module is still half that).

This works out nicely because a P4 with a 200MHz FSB can transfer 4 times per clock (which is why they call it "800MHz"), 8 bytes wide again which is also 6.4 GB/s.

edit: little cleaner formatting

 

[Ryoga]

I wasn't talking about how the bandwidth rating for memory modules is arrived at. I was talking about why they say dual-channel memory is "800 MHz" when the clock speed of the memory bus is really only 200 MHz. One is best called the "data rate" and the other is the clock speed. Basically the same as when you said: "This works out nicely because a P4 with a 200MHz FSB can transfer 4 times per clock (which is why they call it "800MHz"), 8 bytes wide again which is also 6.4 GB/s" except I never referred to the actual bandwidth of the bus.

 

[sunase]

Oh, you did say memory bus. ^^ Sorry, my bad, not enough coffee this morning.

 

[Markfw]

And socket 754 is a single memory control. The socket 939 and 940 are dual memory controllers, but not dual channel in the same sense as the P4 and the nvidia socket A design.

 

[MDE]

Originally posted by: Markfw900
And socket 754 is a single memory control. The socket 939 and 940 are dual memory controllers, but not dual channel in the same sense as the P4 and the nvidia socket A design.

Please explain...