FSB Wall question

I have a question regarding processor fsb walls. Why do they occur? Not factoring in heat dissipation, why are there FSB walls to processors? It seems that these FSB walls only showed up with the Core 2 Duos...I remember with a pentium 4 and some amazing cooling, you can go to about 6 Ghz easily. So, why are there fsb walls to processors?
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  1. I've wondered this too
  2. Well see here, the netburst architecture is designed for high frequencies. There's probably a wall for them too, just much higher. As for why, I have no clue. Does anybody know? I'm curious now...
  3. italy oc'd a pentium 4 to 8ghz...
  4. I believe that the motherboard controllers for the FSB have a tough time keeping up with the high speeds and relaying information like it's supposed to, like the problems with proccesors and voltage leak.
  5. So it's not the processor, it's the motherboard that provides the FSB walls? So CPU frequencies are limitless without factoring in heat?
  6. nightscope said:
    So it's not the processor, it's the motherboard that provides the FSB walls? So CPU frequencies are limitless without factoring in heat?


    Everything will have it's limits.

    I don't think chips have FSB walls, the motherboards they are in do. As new motherboards come out the FSBs get higher and higher.
  7. cnumartyr said:
    Everything will have it's limits.

    I don't think chips have FSB walls, the motherboards they are in do. As new motherboards come out the FSBs get higher and higher.


    Well why do motherboards have fsb walls? It just gets too fast for it to handle? Or too hot?

    Has this ever been tested to prove that chips have no fsb walls?
  8. What motherboard would you test it on? :P

    I consider it like this because noone thought we'd see 400+ MHz FSB quads. It happened on some newer MBs. Now 450-500 MHz quads are slowly starting to appear (same kinds of chips).

    Clock generators on the motherboard would be my guess.
  9. Well someone needs to test this! It just doesn't make sense to me. Higher frequencies result in a higher heat output, but if that is taken care of, then what's stopping the reach of a higher frequency? Blah...blah...blah...
  10. nightscope said:
    Well someone needs to test this! It just doesn't make sense to me. Higher frequencies result in a higher heat output, but if that is taken care of, then what's stopping the reach of a higher frequency? Blah...blah...blah...


    You mean the actual frequency the FSB can run at? The FSB has shedloads of wires on which the signals all have to get to the far end at the same time, plus or minus a small fraction of a clock cycle. Laying them out is hard, and the higher the clock speed the lower the tolerance for variation between signals.

    Also, the speed of light itself is only a foot per nanosecond, so that introduces limits on how far signals can travel at high clock speeds.

    This is why the PC world switched from the parallel AGP bus to serial PCI-Express bus, for example; PCI Express has less wires so it's easier to lay out. More precisely, a 16x PCI-Express bus has lots of wires, but each lane has only four wires that have to be in sync.
  11. Firstly, there is the FSB-strap of the chip in question. There are 3 levels of FSB straps, 800/1066/1333. The lower straps have more aggressive memory latencies than the higher straps. This can cause a 'FSB wall' on chips such as the E2x00 and E4x00 which default to the 800FSB strap. When you push the FSB to extreme levels, the chipset is still trying to communicate with the CPU via the 800FSB strap parameters, which would be too aggressive, and you have a 'FSB wall'. I've seen a mod where an E4300 modded to the 1066FSB strap attained a 70MHz higher FSB than the 800FSB strap.

    Secondly, there is chipset limitation as cnumartyr said. This is especially true in quad cores compared to dual cores. You have (potentially) double the amount of data pumping through the FSB, which puts the chipset under a lot of stress.
  12. Wait...now that I think of it, how about this?

    The wires in the motherboard has a certain size, therefore only so much current can go through it. The thicker the wires, the more current can pass. Basically when you get in the high frequencies the current goes up (because voltage goes up), but it's being limited by the size of the wires in the motherboard. After all, only so much current can get through...OH YEAH and with more current, more resistance is present, thus making it exponentially harder to go faster! It's just like wind resistance ya?

    So who agrees with me? Maybe I'm totally wrong?
  13. nightscope said:
    Well why do motherboards have fsb walls? It just gets too fast for it to handle? Or too hot?

    Has this ever been tested to prove that chips have no fsb walls?


    You can test it yourself if you have an enthusiast class motherboard.

    Suppose, for instance, you have a Q6600. Go into your BIOS and lower CPU multi on your Q6600 to 4 (enthusiast mb's support the CPU multi unlock feature). With the front side bus running at deault 266 MHz (1066), the CPU will be massively underclocked running at less than half its default frequency (266 x 4 = 1066 MHz). By the way, if you really try this, make sure to take the divider off your memory modules (running them 1:1 would be best methinks).

    Now begin to raise the FSB in increments of 20. With a vanilla board (eg 975X), I guess you'll hit the "FSB wall" maybe around 500 MHz? Whatever, let's assume the system starts to cr@p out at 500.

    Obviously, if your system (with CPU multi =4) is conking out with FSB running at 500 MHz, it's not the Q6600 that is overheating, because the CPU is still underclocked and cool at 2.0GHz (500 x 4 = 2000 MHz). Rather, it's the system bus that is running hot and unstable at 88% overclock (266 vs. 500).
  14. easyg said:
    You can test it yourself if you have an enthusiast class motherboard.

    Suppose, for instance, you have a Q6600. Go into your BIOS and lower CPU multi on your Q6600 to 4 (enthusiast mb's support the CPU multi unlock feature). With the front side bus running at deault 266 MHz (1066), the CPU will be massively underclocked running at less than half its default frequency (266 x 4 = 1066 MHz). By the way, if you really try this, make sure to take the divider off your memory modules (running them 1:1 would be best methinks).

    Now begin to raise the FSB in increments of 20. With a vanilla board (eg 975X), I guess you'll hit the "FSB wall" maybe around 500 MHz? Whatever, let's assume the system starts to cr@p out at 500.

    Obviously, if your system (with CPU multi =4) is conking out with FSB running at 500 MHz, it's not the Q6600 that is overheating, because the CPU is still underclocked and cool at 2.0GHz (500 x 4 = 2000 MHz). Rather, it's the system bus that is running hot and unstable at 88% overclock (266 vs. 500).


    It'll happen a lot sooner than 500 MHz on a Q6600. For the record though, PLL/GTL Ref Voltages will help in raising the wall to a point.
  15. easyg, the lowest multi available is 6x, not 4x, but your point still stands.

    I also doubt a 975X would get anywhere NEAR 500MHz with a Q6600... 400MHz maybe... and that is a BIG maybe... ;)
  16. What you are saying makes sense, because you have higher heat when the NB is trying to comunicate with the CPU and at the same time you trying to push more current. There comes a point when the heat is just too much for the mainboard circuit pathways to handle and at anywhere near 500 +FSB you must have lots of fan pointed directly at the motherboard.

    Now with the processer you are dealing with how well it conducts electricity and most CPU chips behave differently even ones from the same waffle or batch. The higher bin processers are granted the names Extreme Editions because they conduct electricity so well thats why at their stock speeds, example; Quad Cores that only need 1.24 volts to run at 3.0GHz while still at stock volts as deemed by Intel.

    The lower bin CPU chips are pushed down to models like the my processer (E6600) that needs more than stock voltages to reach the same speeds as an Extreme Edition, they have gotten much better through revisions and thats why it Soo much smarter to buy a Q6600 instead and overclock it to Extreme Edition levels to save you some major cash!
  17. epsilon84 said:
    easyg, the lowest multi available is 6x, not 4x, but your point still stands.

    I also doubt a 975X would get anywhere NEAR 500MHz with a Q6600... 400MHz maybe... and that is a BIG maybe... ;)



    Oops, sorry, my bad. Thanks to cnumartyr too, for pointing out my mistakes.

    I was just trying to make an example and got a little careless.
  18. Holy crap. Those are some of the worst explanations I have ever heard.

    First of all, the reason for FSB wall is the same reason for any other digital circuit to have a 'wall'. Digital circuits consist of datapath and control. Datapath is stuff like multipliers, adders, etc. Control is the state machine for controlling the dataflow and is implemented using registers. The maximum frequency or the minimum cycle period is equal to the Tsu (flip-flop set up time) + Tprop(propagation time of the datapath) + Tcq(clock to Q of the flip flop). As temperatures decrease, transistors are able to switch faster and all these values decrease. The relationship is very complex because many parameters scale different with temperature. In the end, regardless of how low the temperature is, Tcycle will no longer decrease and the circuit can no longer be clocked lower.

    In addition, some digital circuit elements have a probability of becoming unstable (crossing clock domains). Increasing the frequency results in a higher probability of a circuit instability. So, if it's running fine, it still has a larger probability of failure, etc.

    Oh yeah, there are lots of other factors associated with increasing voltage (more tunneling and leakage) and higher parasitic capacitance
  19. I wanted to make it simple so the beginner could have an easy way to understanding. I did not want to write an SA about capacitors, resistors and transistors. Making yourself feel better by insulting others is wrong and by doing so makes you look bad because you have to put down others to make yourself feel better. Oh I just love your name it shows intelligent. :sarcastic:
  20. Yeah, that makes a bit more sense, but why does instability occur at higher frequencies? So too much stuff is going on for all the components to handle? How can this be fixed? Less wiring? How do newer chipsets offer higher frequencies? Better NB/SB heatsinks?

    So basically, the motherboard is the bottleneck for the CPU?
  21. I thought I would point out the the wall for the C2D is around the same it was for the pentium 4's. Remember that the 8 ghz pentium 4 was running somewhere near I believe a 17 or 18x multiplier, which means. That they only need to reach between 440 and 470 fsb depending on the multiplier used. So with respect to that it appears the walls are similar placed at around 500 fsb (obviously depending on the chip, mainboard, system config, and cooling setup). This is no real technical data that I am presenting, but a mere observation...I just believe saying that the pentium 4's (or rather their chipsets) had a much higher FSB "wall" is slightly inaccurate. Hope this helps!

    Best,

    3Ball
  22. 3Ball said:
    I thought I would point out the the wall for the C2D is around the same it was for the pentium 4's. Remember that the 8 ghz pentium 4 was running somewhere near I believe a 17 or 18x multiplier, which means. That they only need to reach between 440 and 470 fsb depending on the multiplier used. So with respect to that it appears the walls are similar placed at around 500 fsb. This is no real technical data that I am presenting, but a mere observation...I just believe saying that the pentium 4's had a much higher FSB "wall" is slightly inaccurate. Hope this helps!

    Best,

    3Ball


    Oh 3ball you're so technical :P
  23. nightscope said:
    Oh 3ball you're so technical :P


    Yea its just how I roll...lol

    Best,

    3Ball
  24. nightscope said:
    Yeah, that makes a bit more sense, but why does instability occur at higher frequencies? So too much stuff is going on for all the components to handle? How can this be fixed? Less wiring? How do newer chipsets offer higher frequencies? Better NB/SB heatsinks?

    So basically, the motherboard is the bottleneck for the CPU?



    In a sense, yes. But look at the die size of a CPU. They get to their high frequencies by utilizing die shrinks.
    A motherboard is a complicated, BIG piece of architecture that must work with multiple components all running at different speeds, accross very, very long traces and paths by comparison. Some day, everything inside your PC will fit basically into a single integrated chip. The only reason for a "motherboard" will be so you have a place to plug in your input devices, if those are even still needed.
  25. jitpublisher said:
    In a sense, yes. But look at the die size of a CPU. They get to their high frequencies by utilizing die shrinks.
    A motherboard is a complicated, BIG piece of architecture that must work with multiple components all running at different speeds, accross very, very long traces and paths by comparison. Some day, everything inside your PC will fit basically into a single integrated chip. The only reason for a "motherboard" will be so you have a place to plug in your input devices, if those are even still needed.


    So when they're able to fit all of that into one integrated chip, there will be practically no limit to how the frequencies can go? (Not factoring in friction/heat)
  26. If they can fit all of that onto a chip one day, I'll eat my socks, and not just the clean ones.
  27. starcraftfanatic said:
    If they can fit all of that onto a chip one day, I'll eat my socks, and not just the clean ones.


    What's the physics limit? Something like 22nm? Which is like.. 2 more die shrinks for Intel. I can't remember it off the top of my head.
  28. Why doesn't intel jump directly to 22nm instead of 45 nm, etc...?
    Need to master each die shrink can't jump too quickly?
  29. nightscope said:
    Why doesn't intel jump directly to 22nm instead of 45 nm, etc...?
    Need to master each die shrink can't jump too quickly?


    Takes a lot of time to design, convert all current manufacturing to the new process, bug test, research, and all of that stuff.

    That attitude is kind of like.. well why didn't we just jump from the Pentium I to Sandy Bridge? It's a progression and requires a ton of research and development.

    As an example.. the Scroll compressor was theorized back in the late 1800s. The technology to make it work within tolerances was not around until the 1980s with the first scroll being released in 1987. Just an example, but it shows people know what is possible, but the ways to do it may not be worked out yet. Also keep in mind CPUs are probably the most complex item being manufactured on the face of the earth.
  30. I see...

    So lets say this, if we (humans...) discovered how to completely illuminate friction on surfaces, wouldn't that give us the ability to have extremely high frequencies?
  31. nightscope said:
    I see...

    So lets say this, if we (humans...) discovered how to completely illuminate friction on surfaces, wouldn't that give us the ability to have extremely high frequencies?


    As far as I remember they are working on replacing electronics in computers with fiber optics anyways. Think about how much less heat would be generated and information moving at the speed of light within a computer.
  32. Do you think fiber optics will work? Have they done testing on them and insured that they would be a good replacement? Wouldn't things get unstable with them?

    I read a little bit on them but I'm not 100% sure what they're composed of...so if you can shed some light on me in that area it would be appreciated.
  33. nightscope said:
    Do you think fiber optics will work? Have they done testing on them and insured that they would be a good replacement? Wouldn't things get unstable with them?

    I read a little bit on them but I'm not 100% sure what they're composed of...so if you can shed some light on me in that area it would be appreciated.


    It'd work in a similar way of comparing a copper wire to wire a house and the circuitry within the CPU.

    It's the transfer of information. The question is whether or not they can mass produce fiber optics at that level.

    It's just a progression of technology, I'm sure it's only a matter of time.
  34. Is it hard to produce?
  35. latency between areas memory cpu and bridge chip
  36. What does latency have to do with higher frequencies? Higher frequencies help the latency between them.
  37. starcraftfanatic said:
    If they can fit all of that onto a chip one day, I'll eat my socks, and not just the clean ones.


    How big is that SD 2 GB memory chip you have in your phone or camera, or how about the new mini SD chips that are less than half the size of the regular SD's and hold up 4 gb of data? Simply amazing.

    30 years ago 2 GB of memory would have cost over 3 million dollars and would have taken a building half the size of a Wal-Mart Suuper Center to house all of it. It does not pay to doubt what can be pratical in the future.

    Hope you like the taste of your own sweaty feet!
  38. I was referring to fitting all the motherboard components, sound and vid cards, proccesors and everything else onto a single chip.
  39. That would be an astounding thing to achieve. Only a matter of time with all the improvements that are being made.
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