traditional athlon and changes in opteron

Posted on 2006-04-12
Last Modified: 2010-04-26
Athlon processor and north/-southbridge seemed very easy to understand.

But now when I read new article about Opteron and Xeon I'm quite confused.
(this article was on finnish language so I took only the pictures)

1.) Does north-/southbridge exist any more in Opteron?

2.) The article said that the maximum memory bus speed in XEON would be 6,4Gbytes/s but northbridge is too slow. How is that 6,4Gbytes/s calculated?

3.) In dualcore Opteron both cores have their own memory buses. If motherboard has 4 slots for DIMM then are those diveded that Core1 has two slots and core2 has the other two? So should I pay attention to which slot I insert RAM in future?

4.) If XEON has bus speed of 800MHz then FSB would be 200 MHz and to achieve the 2,8GHz the multiplier would be 14. Is that correctly calculated?

5.) If that Opteron is 2,4GHz and the memory bus speed is 2,4Ghz how can I calculate the FSB from that? Would FSB communicate only with AGP anymore in this case?

6.) Opteron has 1MB cache for both cores (1+1MB) and XEON has 2MB cache for both cores (2+2 MB). Was the AMD's key to victory the fast memory bus and Intel only tried it's best to increase the L1 cache?

7.) Is the main reason for lower power consumption on AMD the lower frequency, what would the other reasons be?

8.) Article says that the XEON memory controller is on motherboard, does that mean that NB is the memory controller?

10 points each.
Question by:hafka

    Author Comment

    50 points each then
    LVL 69

    Expert Comment

    1) The Athlon64 (and related Opteron) have an integrated memory controller and Northbridge on-die with a hypertransport bus connected to the outside world:  The Northbridge is actually part of the cpu.

    2) The Xeon Front Side Bus is 800MHz and is 64 bits (8 bytes) wide, so that yields 6.4GB/sec

    3) No, RAM slots are not associated with a particular core.  All the RAM is available to each core, just like multiple cpus.

    4) Correct.

    5) Opterons still use the motherboard FSB, though they don't have a Northbridge.  When using PC3200 RAM, the FSB will be 200MHz and the cpu multiplier is multiplied with this to give you the final cpu speed.  FSB is still used to support the AGP and PCI buses.

    6) Pretty much the case.  The Hypertransport bus is much faster than the FSB, so memory accesses are extremely fast.  The Opteron also has the benefit of more than one of them.

    7) Lower frequency, lower voltage, and Cool N Quiet mode for more power saving.

    8) Yes.

    Author Comment


    On question 2 you said that the FSB speed is 800 MHz, but on question 4 I calculated that 800MHz bus speed gives 200 MHz for FSB.

    Or did you mean that the 6,4Gbytes/s is calculated from the 4*FSB value?

    On question 5 you said that when using PC3200 RAM, the FSB will be 200MHz. What about when using PC4000 or PC2800?
    LVL 69

    Accepted Solution

    >Or did you mean that the 6,4Gbytes/s is calculated from the 4*FSB value?

    This is the case.  The motherboard is using a 200MHz bus speed, but the cpu, in theory, accesses the bus 4x per clock cycle (it actually performs less):

    >On question 5 you said that when using PC3200 RAM, the FSB will be 200MHz. What about when using PC4000 or PC2800?

    To be exact, some motherboards allow you to change the FSB to whatever you like, and stability will depend on the RAM quality and motherboard.  Most motherboards I have will attempt to run PC3200 at 200FSB, if the cpu allows it.  I have run PC3200 at faster speeds, like 250FSB, but it was high quality RAM.  If you use PC4000, you may be able to run it at  a higher FSB, but you may also need to adjust other parameters like lowering HT to keep from overclocking too much.  With PC2700, you may need to run it slower, perhaps at 166FSB, to keep it stable.

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