FSB of Athlon 64 procs

[d4dev]

Would it be right to say that the FSB of an Athlon 64 is 1600 MHz? Since the memory controller is integrated on the processor die, how is this figure arrived at? And lastly, how is it that different Athlon 64s have different FSBs? And where does HyperTransport figure in all this?

 

[arcas]

The Athlon64 doesn't really have an "FSB" since the memory controller is onboard (the FSB for Athlons and Pentiums refers to external bus connecting the CPU to the Northbridge/memory controller). HTT is the closest analog. It's the bus that connects the A64's memory controller to memory.

To get your true HTT speed, you multiply your HTT frequency (normally 200mhz) times your LDT multiplier (normally 5 for s939, 4 for s754). This gives a HTT speed of 1000mhz for socket 939 or 800mhz for socket 754. Since it's a DDR bus, your HTT speeds are effectively 2000mhz and 1600mhz, respectively.

Since the A64 doesn't have a FSB, it also uses the HTT frequency for its internal clock. There is another multipler for this. For example, the Opteron 165 has a multiplier of 9. 9 * 200mhz HTT = 1800mhz CPU speed.

 

[d4dev]

Ahh....ok. And is the HTT of an Opteron processor, lets say the Opteron 146, slower/faster than that of an Athlon 64?

 

[dguy6789]

Originally posted by: d4dev
Ahh....ok. And is the HTT of an Opteron processor, lets say the Opteron 146, slower/faster than that of an Athlon 64?

The Athlon 64 and the Opteron are basically the same thing.

Some Athlon 64s run at a 1600mhz htt and some run at 2000mhz. Same with Opteron.

 

[d4dev]

Thanks a lot guys!! You've been a BIG help!

 

[arcas]

It depends on the model. The socket 940 Opterons built on 0.13 micron process have an 800mhz bus. The socket 940 Opterons built on a 0.09 micron process have a 1000 mhz bus. So far as I know, the socket 939 Opterons are all 0.09 micron so they also have a 1000 mhz bus. Multiply by 2 to get the effective speed.

To be honest, though, there's not much point comparing the HTT speed of, say, a 146 with, say, an A64-3000. HTT is a very fast bus and is nowhere near congested for uniprocessor models whether it's 800mhz or 1000mhz. It's sort of like comparing the bandwidth of a 12-lane highway and a 16-lane highway even though only 6 cars are travelling down them.

(Arguably, the same applies for the 2xx models also. In fact, most lower-end dual s940 boards hang memory off of only one of the sockets meaning that CPU #2 has to use CPU #1 to access memory. So CPU #1's memory HTT bus will be carrying a double load. This is measurable in benchmarks but in non memory-intensive real-world apps, the performance hit is negligible.)

 

[d4dev]

Thanks! That was very informative!

 

[bs200sx]

Please Help Me I Just bought an athlon 3700+ 939 and an asus motherboard a8n5x and the overclocking software is reading that my bus speed is 800mhz and i can't fiqure out how to bring it up to 1000mhz bus 2.2 ghz clock my bios says 200mhz system