general OCing: "system bus vs multipliers" question

[Sunny129]

ok guys...back in the day there were 3 main components to OCing a system: CPU, memory, and the system bus/FSB (i left video cards out b/c i consider that to be peripheral, and not a main system component). for instance, it seemed just as important to OC the system bus on my old P4C 2.6 system as it was to OC the CPU and memory. if i increased the quad-pumped system bus from 200MHz to 250MHz, my FSB would go from 800MHz to 1000MHz. obviously the system bus had to be OCed in order to OC the CPU b/c Pentium 4's at the time did not have unlocked multipliers. memory relied on the system bus to a much lesser extent thanks to the use of FSB : DRAM ratios (which more or less functioned as multipliers for the memory)...but at the end of the day, typically a combination of a particular FSB : DRAM ratio and a tweaked FSB was necessary to OC memory with sufficient accuracy.

we now live in a world of CPUs w/ unlocked multipliers (well not really, but a good number of CPUs today allow multiplier manipulation). i understand the benefit of having access to both the system bus and multipliers for OCing, but i'm on the fence about the importance of the system bus speed these days. back in the days of the Pentium 4, there were no IMCs (integrated memory controllers) or on-die north bridges (CPU-NBs). in other words, the FSB could not be changed using multipliers, and could only be changed by changing the system bus speed. these days we have the CPU-NB and the HT Link, whose speeds can be changed not only by manipulating the system bus directly, but also by changing multipliers...

...which finally brings me to my question. i see people OCing their unlocked-multiplier CPUs using multipliers only (with regard to CPU frequency, CPU-NB frequency, and HT Link frequency), and very little or no OCing using the system bus. for instance, i see some folks OCing their 1090Ts to ~4GHz (and CPU-NBs & HT Links to ~2600MHz) using nothing but the CPU multiplier, CPU-NB multiplier, and HT Link multiplier, and leaving the system bus at the default 200MHz. is there a reason some of these folks aren't using slightly lower multipliers and a higher system bus speed? again, back in the day, not only was it necessary to OC the system bus in order to OC the CPU and memory, but it was also important b/c it gave your FSB a boost too.

the only reason for not OCing the system bus that would make sense to me is if today's HT Link is the modern-day equivalent to yesterday's FSB. if that were the case, i can see how HT Link can be OCed by multiplier alone. is this a misinterpretation? if it is, then i'm still not clear on why some folks are using just multipliers, and no system bus, to OC.


TIA,
Eric

 

[superccs]

OCing via the multiplier option of a cpu puts less stress on the board, though OCing the FSB can bump system speed and provide the desired effect of a complete OC. I think a blend of both would be optimal, and for Phenom II's the HT bus speed I think has an optimal speed of 2200-2400 (though I forgot the test that shows that).

Either way the unlocked CPUs give greater flexibility, but only sometimes give greater peak overclock. ie a 1055T will clock to roughly the same as many 1090T at around 4.0-4.2Ghz.

Hope that helps.

I have no idea how the new i7, i5, i3s overclocking works, but I think its a completely different story.

 

[Sunny129]

well from the looks of it, it seems like your response is a confirmation of my thoughts regarding today's HT Link and yesterday's FSB. back in the day it was necessary to OC the system bus (or base clock) in order to raise the FSB since it did not have a multiplier (or an unlocked/accessible multiplier anyways). nowadays it seems that the HT Link can be OCed by either increasing the system bus (base clock) OR by increasing a multiplier or ratio.

so the conclusion i'm drawing is that OCing the system bus (base clock) is not that important nowadays for a few reasons:
1) with an unlocked CPU, one doesn't have to rely on OCing the base clock to increace CPU frequency.
2) the CPU-NB is changeable via a multiplier or ratio, making it again unnecessary to use the base clock to OC it.
3) the HT Link is also changeable via a multiplier or ratio, making it also unnecessary to use the base clock to OC it.

its making more and more sense to me why some folks are strictly OCing with multipliers. i guess it is b/c those with an unlocked CPU can OC the CPU, the CPU-NB, and the HT Link without even touching the base clock. this actually makes perfect sense in my head...is this accurate, or am i deluding myself lol?

 

[aigomorla]

Depending on the cpu, 1 is greater then the other.

And also family line.

Bclk will change other values like QPI and PCI-E if its on a shared multiplier.

Multi's usually dont change anything beause your using the standard bclk.

Put simply.. bclk is a adjustment which we can do on the board side.
Its unlocked via board side though bios by most vendors.

Multi is done straight on the microcode. This can not be changed by anyone except intel.

 

[soccerballtux]

I recently changed my overclock from multi-only (17.5*200) to a bus overclock. The bus on my chip can't go past about 225, up from 200, stable, but even then that made things like firefox a LOT faster at simple stuff like smoothscroll and UI responsiveness-- even though it's running at 2.2ghz when not under load.
I would go further if I could.

 

[Cogman]

ok guys...back in the day there were 3 main components to OCing a system: CPU, memory, and the system bus/FSB (i left video cards out b/c i consider that to be peripheral, and not a main system component). for instance, it seemed just as important to OC the system bus on my old P4C 2.6 system as it was to OC the CPU and memory. if i increased the quad-pumped system bus from 200MHz to 250MHz, my FSB would go from 800MHz to 1000MHz. obviously the system bus had to be OCed in order to OC the CPU b/c Pentium 4's at the time did not have unlocked multipliers. memory relied on the system bus to a much lesser extent thanks to the use of FSB : DRAM ratios (which more or less functioned as multipliers for the memory)...but at the end of the day, typically a combination of a particular FSB : DRAM ratio and a tweaked FSB was necessary to OC memory with sufficient accuracy.

we now live in a world of CPUs w/ unlocked multipliers (well not really, but a good number of CPUs today allow multiplier manipulation). i understand the benefit of having access to both the system bus and multipliers for OCing, but i'm on the fence about the importance of the system bus speed these days. back in the days of the Pentium 4, there were no IMCs (integrated memory controllers) or on-die north bridges (CPU-NBs). in other words, the FSB could not be changed using multipliers, and could only be changed by changing the system bus speed. these days we have the CPU-NB and the HT Link, whose speeds can be changed not only by manipulating the system bus directly, but also by changing multipliers...

...which finally brings me to my question. i see people OCing their unlocked-multiplier CPUs using multipliers only (with regard to CPU frequency, CPU-NB frequency, and HT Link frequency), and very little or no OCing using the system bus. for instance, i see some folks OCing their 1090Ts to ~4GHz (and CPU-NBs & HT Links to ~2600MHz) using nothing but the CPU multiplier, CPU-NB multiplier, and HT Link multiplier, and leaving the system bus at the default 200MHz. is there a reason some of these folks aren't using slightly lower multipliers and a higher system bus speed? again, back in the day, not only was it necessary to OC the system bus in order to OC the CPU and memory, but it was also important b/c it gave your FSB a boost too.

the only reason for not OCing the system bus that would make sense to me is if today's HT Link is the modern-day equivalent to yesterday's FSB. if that were the case, i can see how HT Link can be OCed by multiplier alone. is this a misinterpretation? if it is, then i'm still not clear on why some folks are using just multipliers, and no system bus, to OC.


TIA,
Eric

Ok, I think you are getting terms mixed up. First off, the system bus IS the FSB. You seem to be using those terms as two separate things. I could see how Intels and AMDs terminology for it could make things confusing, but suffice it to say that the front side bus and the system bus are the exact same thing.

Second, Overclocking the multiplier doesn't affect (or at least, it very minimally affects) the system bus. If you aren't changing the numbers from say 9x to 10x, then you aren't changing the multiplier.

Now the question, why one or the other? Overclocking via a higher FSB provides more benefits than overclocking via multiplier. By using the FSB only, you not only increase the speed of the CPU, but the speed of all devices connected to the FSB. This increase of system performance means that a system overclocked only with the FSB will be faster than one overclocked only with the CPU multiplier (Assuming that dividers don't screw things up). In theory at least.

The reason you overclock only the multiplier is that you want to see how fast your CPU can go without limiting it to your ram, video card, etc. Multiplier overclocks are generally more stable than FSB overclocks.

Now, in practice, a FSB overclock generally don't provide THAT much of a gain over multiplier overclocks. Memory access speeds really aren't that big of a game changer (sorry 5333 DDR40 sellers).

 

[Sunny129]

Ok, I think you are getting terms mixed up. First off, the system bus IS the FSB. You seem to be using those terms as two separate things. I could see how Intels and AMDs terminology for it could make things confusing, but suffice it to say that the front side bus and the system bus are the exact same thing.

Second, Overclocking the multiplier doesn't affect (or at least, it very minimally affects) the system bus. If you aren't changing the numbers from say 9x to 10x, then you aren't changing the multiplier.

Now the question, why one or the other? Overclocking via a higher FSB provides more benefits than overclocking via multiplier. By using the FSB only, you not only increase the speed of the CPU, but the speed of all devices connected to the FSB. This increase of system performance means that a system overclocked only with the FSB will be faster than one overclocked only with the CPU multiplier (Assuming that dividers don't screw things up). In theory at least.

The reason you overclock only the multiplier is that you want to see how fast your CPU can go without limiting it to your ram, video card, etc. Multiplier overclocks are generally more stable than FSB overclocks.

Now, in practice, a FSB overclock generally don't provide THAT much of a gain over multiplier overclocks. Memory access speeds really aren't that big of a game changer (sorry 5333 DDR40 sellers).

ok, i thought i might be going astray with the terminology. so then the system bus, front side bus, and base clock are all just different names for the same concept. in fact, looking back to the introduction of the Pentium 4, i see that i had the terminology mixed up then too. you see, back then i used the terms system bus and base clock interchangeably, but thought that the actual FSB was 4X the base clock simply b/c the launch of the P4 era was also the launch of quad-pumped FSBs. but looking back, i see that folks at the time generally didn't refer to the FSB at its face value. that is, if a P4 CPU ran on a 100MHz FSB, even though the FSB is quad-pumped and effectively 400MHz, people still equated the base clock value of 100MHz with FSB.

i thank you for helping get the terminology straight, but i'm still kind of left wondering if i'll truly have a faster system OCing with the FSB than i will by OCing with multipliers only, on a Phenom II platform that is. one of the points i tried to make in my original post before posing my question was that, back in the day there was no doubt that FSB OCing made for a faster system than multiplier OCing did, due to the fact that FSB OCing would OC not just the CPU, but other devices running on the FSB as well (the exact reason you stated above). but if i OC the CPU, CPU-NB, and HT Link all via multiplier (as we have the ability to do that these days), what devices running on the FSB are being left not OCed?

 

[maniac5999]

I am also interested in this. I have a Phenom II 940. Individually, the core is stable to 3.4ghz, NB/HT to 2300mhz, and memory to about 1080mhz. However if I try to tie everything together with Base Clock/FSB overclocking I can only end up with 3.36/2160/960. beyond the three settings that I mentioned, what am I increasing when I overclock using the FSB?

 

[biostud]

Unless you want to run your CPU right to the limit, it doesn't really matter. The speed difference is very small, and even if it limits your CPU to 3.8Ghz instead of 4Ghz you're not going to notice the difference.

 

[maniac5999]

Unless you want to run your CPU right to the limit, it doesn't really matter. The speed difference is very small, and even if it limits your CPU to 3.8Ghz instead of 4Ghz you're not going to notice the difference.

Obviously we're talking about small gains and losses here and there, but my interest is partially academic -I like to know how stuff works- and partly for fun. -I like overclocking my computer- Does changing Bclk/FSB change anything like L2/L3 speed or is it just a workaround for the 90% of people who don't have an unlocked multiplier?

 

[maniac5999]

Does ANYONE know? When I increase the Bclk am I increasing anything beyond what can be increased individually in the BIOS with a BE processor? L2? L3? Magical pixie fairy dust? I'm shocked that nobody on the site seems to know.

 

[RaistlinZ]

As far as I know L2/L3 cache run at the same speed of your CPU always. So, if you increase your CPU speed by upping the multiplier or by increasing the Bclk, or both, then yes your L2/L3 will also be running faster.

Someone please correct me if I'm wrong though.

 

[maniac5999]

As far as I know L2/L3 cache run at the same speed of your CPU always. So, if you increase your CPU speed by upping the multiplier or by increasing the Bclk, or both, then yes your L2/L3 will also be running faster.

Someone please correct me if I'm wrong though.

Interesting. In that case, I guess I should just set my clock back to 200mhz and just increase all the multipliyers.

 

[Sunny129]

Obviously we're talking about small gains and losses here and there, but my interest is partially academic -I like to know how stuff works- and partly for fun. -I like overclocking my computer- Does changing Bclk/FSB change anything like L2/L3 speed or is it just a workaround for the 90% of people who don't have an unlocked multiplier?

+1

my original question was not a "should i OC via multipliers, the FSB, or a combination thereof" - rather it was a simple "what is the exact difference between OCing with multipliers only, and OCing with FSB only" question.

as i've stated a few times already in previous posts, its easy to see how back in the day an increase in FSB/base clock freq. resulted in the OC of more than just the CPU. for instance, FSB/base clock OCing was required in order to OC a locked CPU (and still is today). likewise, FSB/base clock OCing was required in order to OC the effective FSB (double-pumped for older Athlon XP systems, and quad-pumped for older P4 systems). most boards were pretty good about offering a PCI bus freq. lock so that it wouldn't run out of spec while OCing the FSB. and while memory was proportional to the FSB freq., some manipulation was usually available via FSB : RAM ratios (and still is today).

today however, it would appear that the only thing dependent on FSB OCing would be the memory which, although it can be manipulated via FSB : DRAM ratios, still requires manipulation of the FSB to fine-tune the memory frequency. otherwise, a CPU with an unlocked multiplier doesn't require FSB OCing to be OCed, the CPU-NB doesn't require FSB OCing b/c it has unlocked multipliers, and the HT Link/effective FSB doesn't require FSB/base clock OCing b/c it also has unlocked multipliers these days.

my CPU is a Phenom II X6 1090T. if i wanted to OC it from the default 3.2GHz up to 3.6GHz, i could either leave the FSB/base clock alone and increase the multiplier to 18 (18 x 200 = 3600MHz), or i could leave the multiplier at 16 and increase the FSB/base clock to 225MHz (16 x 225 = 3600MHz). if i went the FSB/base clock OCing route, my HT Link freq. would increase from the default 2GHz up to 2.25GHz (10 x 225 = 2250MHz). but i could just as well achieve an HT Link speed of 2.25GHz by increasing the multiplier and leaving the FSB/base clock freq. alone (11.25 x 200 = 2250MHz...i know there's no 11.25 multiplier, but this is just hypothetical).

simply put, the question is this: if we OC all these components to the desired level by OCing the FSB/base clock and leaving all the multipliers untouched, what additional buses/components/whatever are also getting OCed that wouldn't get OCed were we to OC to the same CPU/CPU-NB/HT Link frequencies using only multipliers?

that's about as clear as i can make the question at hand...