Question Is FSB and BCLK same thing? why are they different in my computer?

[Yanif]

My system is i7-4790K on Asus Z97-pro Gamer motherboard. I have manually set BCLK at 100 mhz, CPU multiplier at 46, and cache multiplier at 44 in BIOS. When I set DRAM frequency at 2200 mhz, CPUID showed fsb:dram ratio at 1:11. Since this setting was a bit unstable, I changed DRAM frequency to 2133 mhz. To my surprise, the fsb:dram is now 1:8 as indicated by CPUID. Does it mean that my FSB is 133 mhz now? How can FSB be different from BCLK? My second question is this: Was 1:11 a bad ratio thus caused system instability? or was 2200 mhz set too high? Are there fsb:dram numbers that computer favors more than other numbers? I appreciate any help and thoughts,

 

[CountMike]

My system is i7-4790K on Asus Z97-pro Gamer motherboard. I have manually set BCLK at 100 mhz, CPU multiplier at 46, and cache multiplier at 44 in BIOS. When I set DRAM frequency at 2200 mhz, CPUID showed FSB😀RAM ratio at 1:11. Since this setting was a bit unstable, I changed DRAM frequency to 2133 mhz. To my surprise, the FSB😀RAM is now 1:8 as indicated by CPUID. Does it mean that my FSB is 133 mhz now? How can FSB be different from BCLK? My second question is this: Was 1:11 a bad ratio thus caused system instability? or was 2200 mhz set too high? Are there FSB😀RAM numbers that computer favors more than other numbers? I appreciate any help and thoughts,

FSB (older term) and BCLK are practically same thing, providing connection between CPU and memory, PCI(e) and other parts. Changing FSB/BCLK also affects those components.
For instance, CPU multiplier x FSB frequency = CPU frequency , same goes for RAM and PCI but with some predetrmined dividers.

 

[Yanif]

FSB (older term) and BCLK are practically same thing, providing connection between CPU and memory, PCI(e) and other parts. Changing FSB/BCLK also affects those components.
For instance, CPU multiplier x FSB frequency = CPU frequency , same goes for RAM and PCI but with some predetrmined dividers.

Appreciate your feedback.
I am pretty sure that my CPU still runs at 4.6 GHz after changing DRAM frequency. HWmonitor says so. Since the multiplier was fixed at 46 in BIOS, that only means BCLK is still at 100 MHz. If FSB is same as BCLK, then how come the FSB:RAM ratio is 1:8 as indicated by CPUID? Should the ratio be 1:10.66? I am deeply puzzled by this mystery.

 

[CountMike]

Appreciate your feedback.
I am pretty sure that my CPU still runs at 4.6 GHz after changing DRAM frequency. HWmonitor says so. Since the multiplier was fixed at 46 in BIOS, that only means BCLK is still at 100 MHz. If FSB is same as BCLK, then how come the FSB:RAM ratio is 1:8 as indicated by CPUID? Should the ratio be 1:10.66? I am deeply puzzled by this mystery.

FSB/BCLK affect memory frequency, not other way around. You can change RAM frequency but it wouldn't change FSB. Divider is there to restore relation of RAM frequency to internal memory controller in the CPU. There's also SPD and XMP that describe RAM capability to BIOS so it can set all those values properly.
PCI and PCIe are also affected by FSB Higher FSB would also cause higher PCI(e) which needs to be as close to 100MHz as possible as not only GPU is connected to it but also disk controller (unless there's a separate chip for it) and some other ones. Dividers once again come to help so FSB frequency doesn't exceed what's best for it. Some BIOSes can adjust it automatically and some may have manual adjustment but those parts need to stay at 100MHz no matter which FSB frequency or troubles may ensue.

 

[Yanif]

FSB/BCLK affect memory frequency, not other way around. You can change RAM frequency but it wouldn't change FSB. Divider is there to restore relation of RAM frequency to internal memory controller in the CPU. There's also SPD and XMP that describe RAM capability to BIOS so it can set all those values properly.
PCI and PCIe are also affected by FSB Higher FSB would also cause higher PCI(e) which needs to be as close to 100MHz as possible as not only GPU is connected to it but also disk controller (unless there's a separate chip for it) and some other ones. Dividers once again come to help so FSB frequency doesn't exceed what's best for it. Some BIOSes can adjust it automatically and some may have manual adjustment but those parts need to stay at 100MHz no matter which FSB frequency or troubles may ensue.

Yes, you explanation makes sense, but I am still puzzled. Here is the gist of my question as shown by the cpu-z screenshot above.

It shows DRAM freq at 1066 MHz. It also shows fsb:dram at 1:8, which means DRAM frequency at 800 MHz. Now do you think the two numbers contradict each other? So which frequency my RAM is running at?

 

[CountMike]

Yes, you explanation makes sense, but I am still puzzled. Here is the gist of my question as shown by the cpu-z screenshot above.

It shows DRAM freq at 1066 MHz. It also shows fsb:dram at 1:8, which means DRAM frequency at 800 MHz. Now do you think the two numbers contradict each other? So which frequency my RAM is running at?

No, you don't divide by 2, you multiply that number with 2 to get effective RAM frequency.
1066.5 x2 = 2133MHz.

 

[Yanif]

No, you don't divide by 2, you multiply that number with 2 to get effective RAM frequency.
1066.5 x2 = 2133MHz.

Even if you multiply by 2, my question is still the same---there are two different speeds: 1600 MHz by fsb;dram ratio, and 2133 MHz by dram speed. So which is the real one?

That is why I doubt FSB being the same as BCLK. If FSB is 133 MHz, then the two numbers can be reconciled. I know that raises more questions. Obviously something does not add up here. What is it?

 

[CountMike]

Even if you multiply by 2, my question is still the same---there are two different speeds: 1600 MHz by fsb;dram ratio, and 2133 MHz by dram speed. So which is the real one?

That is why I doubt FSB being the same as BCLK. If FSB is 133 MHz, then the two numbers can be reconciled. I know that raises more questions. Obviously something does not add up here. What is it?

 

[CountMike]

Both are real because it's DDR memory (Double Data Rate) just depends what is reporting what. More about it https://en.wikipedia.org/wiki/DDR_SDRAM

 

[Yanif]

Both are real because it's DDR memory (Double Data Rate) just depends what is reporting what. More about it https://en.wikipedia.org/wiki/DDR_SDRAM

Sorry I don't understand what you mean. How can one thing having two different values at the same time? It is like saying my car travels at 16 mph and 21 mph at the same time, since both speed are real. No. Both cannot be real. Two different speed means at least one of them is incorrect.

Likewise, DRAM cannot be running at 1600 MHz and 2133 MHz at the same time. I read the wikipedia article and I did not see the claim that DRAM can operate at two frequencies at the same time. Or did I miss something?

 

[CountMike]

Sorry I don't understand what you mean. How can one thing having two different values at the same time? It is like saying my car travels at 16 mph and 21 mph at the same time, since both speed are real. No. Both cannot be real. Two different speed means at least one of them is incorrect.

Likewise, DRAM cannot be running at 1600 MHz and 2133 MHz at the same time. I read the wikipedia article and I did not see the claim that DRAM can operate at two frequencies at the same time. Or did I miss something?

There's actual frequency (1066), and than there's what you can take as "performance effect as if it was running at 2133MHZ), Have a look at chart here https://www.microcontrollertips.com/understanding-ddr-sdram-faq/

View: https://www.youtube.com/watch?v=DLM20pWqMyU

 

[Yanif]

There's actual frequency (1066), and than there's what you can take as "performance effect as if it was running at 2133MHZ), Have a look at chart here https://www.microcontrollertips.com/understanding-ddr-sdram-faq/

View: https://www.youtube.com/watch?v=DLM20pWqMyU

My question is not about bus rate (DRAM) of 1066 MHz, vs the double data rate (DDR) of 2133 MHz. The two numbers, although different, actually describe the same frequency. They are different because the unit of measurement is different. It is like describing speed in terms of mph and kmph. You having two different numbers does not mean there are two speeds. There is no contradiction here. So let's stick with same unit of measurement so that we don't end up with having two numbers to describe the same speed. One number one speed is easier for both of us.

Therefore, please don't bring in DDR frequency when I am talking about DRAM frequency, and vice versa. You are just confusing yourself by doing this and changing my question into something I never asked. So with that understanding let me rephrase my question into two versions. You can pick either one of them depending on your choice of talking either DRAM frequency or DDR frequency.

DRAM frequency version: From the cpu-z screen shot, you can see DRAM frequency is 1066 MHz. From fsb:dram ratio of 8, it should be 800 MHz. My question is why they are different? The only way to reconcile the difference is making FSB=133 MHz. However you said previously that FSB is the same as BCLK, which should be at 100 MHz. Do you have any explanation?

DDR frequency version: From the screen shot, you can see DDR frequency is 2133 MHz (1066 multiplied by 2). From fsb:dram ratio of 8, it is 1600 MHz. My question is why they are different? The only way to reconcile the difference is making FSB=133 MHz. However you said previously that FSB is the same as BCLK, which should be at 100 MHz. Do you have any explanation?

I apologize if I mixed up DRAM and DDR in my previous question. I hope I clarified here what I am asking by breaking down my question into two versions, so that you can stick with one version. Thank you.

 

[CountMike]

My question is not about bus rate (DRAM) of 1066 MHz, vs the double data rate (DDR) of 2133 MHz. The two numbers, although different, actually describe the same frequency. They are different because the unit of measurement is different. It is like describing speed in terms of mph and kmph. You having two different numbers does not mean there are two speeds. There is no contradiction here. So let's stick with same unit of measurement so that we don't end up with having two numbers to describe the same speed. One number one speed is easier for both of us.

Therefore, please don't bring in DDR frequency when I am talking about DRAM frequency, and vice versa. You are just confusing yourself by doing this and changing my question into something I never asked. So with that understanding let me rephrase my question into two versions. You can pick either one of them depending on your choice of talking either DRAM frequency or DDR frequency.

DRAM frequency version: From the cpu-z screen shot, you can see DRAM frequency is 1066 MHz. From fsb:dram ratio of 8, it should be 800 MHz. My question is why they are different? The only way to reconcile the difference is making FSB=133 MHz. However you said previously that FSB is the same as BCLK, which should be at 100 MHz. Do you have any explanation?

DDR frequency version: From the screen shot, you can see DDR frequency is 2133 MHz (1066 multiplied by 2). From fsb:dram ratio of 8, it is 1600 MHz. My question is why they are different? The only way to reconcile the difference is making FSB=133 MHz. However you said previously that FSB is the same as BCLK, which should be at 100 MHz. Do you have any explanation?

I apologize if I mixed up DRAM and DDR in my previous question. I hope I clarified here what I am asking by breaking down my question into two versions, so that you can stick with one version. Thank you.

DDR is type of (S)DRAM, practically same thing https://whatis.techtarget.com/definition/SDRAM-synchronous-DRAM
DDR signal is generated on the UP and DOWN part of square wave while older RAM that you might call now used only high or low values of square wave. Some programs only detect and display square wave frequency and so show only that frequency while real data frequency is double that.

 

[Yanif]

DDR is type of (S)DRAM, practically same thing https://whatis.techtarget.com/definition/SDRAM-synchronous-DRAM
DDR signal is generated on the UP and DOWN part of square wave while older RAM that you might call now used only high or low values of square wave. Some programs only detect and display square wave frequency and so show only that frequency while real data frequency is double that.

Agree. Like I said, although DRAM and DDR frequencies are different, they are the same thing because the latter is the speed of data, which is the double of the former, which is the speed of bus.

However, I don't see this discussion going anywhere if you keep talking about things both of us fully understand, and trying to answer a question I never asked.

How about my question? I trust you to know that it is not about DRAM vs DDR difference? Do you have any thoughts?

 

[drea.drechsler]

...
How about my question?
...

On the assumption you're referring to your original question....

Technically FSB and BCLK are very different even though people use the terms to refer to the same thing. Correctly and technically, BCLK refers to the clock signal input used for synchronizing communication and operation of any data bus...it could be PCIe bus, the DDR4 bus, RS-232 bus, RS-488 bus. FSB is one specific bus, the Front Side Bus, that provides data communication between the CPU and the northbridge. In current parlance by general computer users, however, they are essentially the same thing.

Since the functions of the northbridge have been entirely taken onboard the CPU in modern SoC (Sysetm on Chip) architecture the FSB correctly is internal to the CPU. But people commonly apply old terms to new paradigms so, whether correctly or incorrectly, they think of the FSB broadly as all the busses used (PCIe, SATA, USB, DDR4, etc.) connecting the CPU to all the devices on them.

In this way of thinking (on Ryzen systems, at least) the BCLK is the clock signal(s) being sent to all the devices that talk directly to the CPU, and the CPU itself, so that they are in sync and talking together. Since it's the master clock signal (in my way of thinking, it should be called MCLK or Master Clock) everything will adjust their internal clock speeds to stay in sync.

Since increasing the MCLK also increases it's internal clocks the CPU will increase clock speed without bothering with multipliers, it was the 'handle' motherboard mfr's gave users who wished to overclock multiplier locked processors. Back in the day, peripherals had a lot more tolerance to clock variations but that's changed as everybody is squeaking out the last bit of performance. Even so, power users still use it to tweak performance but it's very dangerous without very careful stress testing and preparations to handle a lost HDD or SDD should it go badly.

Because FSB is poorly defined in the context of modern SoC systems I think some people also think of the Infinity Fabric, on Ryzen, as the FSB. At least, its been the way I've been able to interpret many confusing posts to be a little less so. In that vein, I can imagine some using it to refer to the Ring Bus on Intel systems.

So in summary, FSB and BCLK are very different and yet used interchangeably by average users and even to refer to disparate things. Understanding what someone's referring to frequently takes a little bit of interpretation in the context of the system they're talking about.

 

[Yanif]

On the assumption you're referring to your original question....

Technically FSB and BCLK are very different even though people use the terms to refer to the same thing. Correctly and technically, BCLK refers to the clock signal input used for synchronizing communication and operation of any data bus...it could be PCIe bus, the DDR4 bus, RS-232 bus, RS-488 bus. FSB is one specific bus, the Front Side Bus, that provides data communication between the CPU and the northbridge. In current parlance by general computer users, however, they are essentially the same thing.

Since the functions of the northbridge have been entirely taken onboard the CPU in modern SoC (Sysetm on Chip) architecture the FSB correctly is internal to the CPU. But people commonly apply old terms to new paradigms so, whether correctly or incorrectly, they think of the FSB broadly as all the busses used (PCIe, SATA, USB, DDR4, etc.) connecting the CPU to all the devices on them.

In this way of thinking (on Ryzen systems, at least) the BCLK is the clock signal(s) being sent to all the devices that talk directly to the CPU, and the CPU itself, so that they are in sync and talking together. Since it's the master clock signal (in my way of thinking, it should be called MCLK or Master Clock) everything will adjust their internal clock speeds to stay in sync.

Since increasing the MCLK also increases it's internal clocks the CPU will increase clock speed without bothering with multipliers, it was the 'handle' motherboard mfr's gave users who wished to overclock multiplier locked processors. Back in the day, peripherals had a lot more tolerance to clock variations but that's changed as everybody is squeaking out the last bit of performance. Even so, power users still use it to tweak performance but it's very dangerous without very careful stress testing and preparations to handle a lost HDD or SDD should it go badly.

Because FSB is poorly defined in the context of modern SoC systems I think some people also think of the Infinity Fabric, on Ryzen, as the FSB. At least, its been the way I've been able to interpret many confusing posts to be a little less so. In that vein, I can imagine some using it to refer to the Ring Bus on Intel systems.

So in summary, FSB and BCLK are very different and yet used interchangeably by average users and even to refer to disparate things. Understanding what someone's referring to frequently takes a little bit of interpretation in the context of the system they're talking about.

If I understand you correctly, are you now saying that fsb (as defined by the programmers who wrote cpu-z, whatever that is) frequency could be different from bclk frequency? My system is not AMD but Intel i7-4790k, BTW.

That is actually what I suspected from the very beginning---my bclk frequency is 100 MHz and fsb frequency is 133 MHz, which is the only way to reconcile the numbers appear on the cpu-z screenshot.

If so, it worth noting that you have changed from your initial position that bclk frequency is same as fsb frequency.

 

[drea.drechsler]

If I understand you correctly, are you now saying that fsb (as defined by the programmers who wrote cpu-z, whatever that is) frequency could be different from bclk frequency? My system is not AMD but Intel i7-4790k, BTW.
....
If so, it worth noting that you have changed from your initial position that bclk frequency is same as fsb frequency.

I honestly can't say what CPU-z is calling the FSB as I'm not familiar with modern Intel systems but it's entirely possible they are different. The point I was making is FSB and BCLK definitions are somewhat fluid and vary a lot based on the system and how people use, or misuse, them in a context different from what they understand them to be.

In context of Ryzen systems, FSB and BCLK are very frequently used to refer to the same thing. Since that's the context I typically work in, I'm not really changing.

 

[Yanif]

I honestly can't say what CPU-z is calling the FSB as I'm not familiar with modern Intel systems but it's entirely possible they are different. The point I was making is FSB and BCLK definitions are somewhat fluid and vary a lot based on the system and how people use, or misuse, them in a context different from what they understand them to be.

In context of Ryzen systems, FSB and BCLK are very frequently used to refer to the same thing. Since that's the context I typically work in, I'm not really changing.

OOPS. In last comment I mistook you for the first guy who responded to my question. Sorry. Now I understand you really did not change your position.

When I set DRAM at 1100 MHz, the fsb:dram ratio was 1:11 as reported by cpu-z. When I set DRAM at 1066 but did not touch anything else, the ratio became 1:8! It was such a surprise because I also had the impression that fsb is same as bclk. It means the motherboard changed fsb on its own, and fsb is not the same as bclk!

I don't recall there is a fsb setting in BIOS. What I set in BIOS is 3 "auto" for CPU Strap, PLL Selection, Filter PLL, and one manual 100.0 for BCLK frequency. Maybe between auto CPU strap and auto PLL selection the motherboard decided a ratio of 1:8 is more elegant than 1:10.66?

If motherboard changed "front side bus" frequency in response to a different DRAM frequency, does it imply FSB connects only CPU and RAM?

Incidently, my GPU is hitting "reliable voltage limit", "operational voltage limit", and "power limit" all the time these days as reported by HWMonitor. Does it have anything to do with FSB frequency?