Memory Bus vs. ICM vs. CPU Clock (FX-8320)

[Cryovenom]

Hi Guys,

So I've been out of the overclocking scene for years now, and haven't really done any serious tweaking since working at a computer store during college in the early 2000s. I recently (as in, last night) bought a new mobo/chip/ram/PSU combo and figured it'd be fun to get back into tweaking and OC'ing again.

Last time I did this, things were much simpler. Your RAM and the bus it was on ran at a certain speed, so you'd set the RAM bus speed, set the multiplier, and RAM Speed * Multiplier = CPU Speed. Simple enough. Play with the voltages and memory timings a bit and you were done.

My new setup is an AMD FX-8320 on a Gigabyte GA-970A-D3 with 2x4GB of Corsair Vengeance 1600MHz DDR3 , and I have to admit I'm a little lost on it. Now it looks like there's the RAM speed, then the IMC (Integrated Memory Controller?) speed which is different, and then the multiplier, and somehow they end up determining your CPU speed.

What I'm trying to figure out is how much room my 1600MHz RAM gives me for overclocking, and how the RAM speed and the IMC speed relate to each other. What is the "stock" setting for RAM, IMC and Multiplier with this chip, and how does changing one (say, RAM or IMC) affect the others?

I found something saying the IMC runs at 2200MHz, but I can't imagine the system would require 2200MHz capable memory in order to run stock clocks, so what gives?

Jon

 

[EarthDog]

Well, first, overclocking ram, unless you are benchmarking or using the integrated GPU, yields little to no results (real world).

That said... your clock speed is still a result of the HTref(FSB) x system multiplier. You memory also has a multiplier which is based off the HTref.

The IMC speed to which you are referring to is actually the NB speed.

 

[Cryovenom]

So I need to figure out the HTref speed, and changing that changes both the RAM and CPU speeds based off the multipliers they use? And what does the NB speed do?

Since Ram speed is HTRef * a multiplier, does that mean that it no longer matters which speed RAM you pick up? Could I run this same proc with 1066, 1333, 1600 and 2000MHz ram and have all of them run at their max speeds without actually affecting anything at all?

Sorry, I'm still kind of confused on this.

 

[EarthDog]

Im not an AMD guy...however, while you wait for someone more versed in this, in my signature is a link to a bulldozer overclocking guide. Check that out... and GL!

 

[Cryovenom]

Thanks!

 

[Conumdrum]

We also have an AMD CPU forum, so ask a mod to move your post there, you'll get better action there.

 

[Cryovenom]

Is this an AMD-specific thing? I posted it here figuring that it would be the kind of thing that applied to any modern CPU and it's kind of a RAM and Mobo question too so I didn't know where exactly it should go.

Edit: I've cross-posted in the AMD CPU forum and we'll see what happens. Thanks for the help guys.

 

[EarthDog]

AMD is pretty different from Intel, yes..I didnt notice it wasnt in the right forum, LOL!

For example, Intel has bclk(FSB/HTref) and system multiplier and memory multiplier, however there isnt a "NB" clock speed to contend with, so its best in the AMD section... agreed.

You see the "!" button? You can use that to report the thread and ask it to be moved.

 

[MattNo5ss]

Moved to AMD CPUs

 

[Cryovenom]

That AMD article in EarthDog's sig is actually really useful for this. What I've figured out so far is:

- Stock FSB speed is "always" 200MHz stock for AMD CPUs
- FSB * DRAM Multiplier * 2 = RAM Speed (meaning that yes, you can run any RAM speed you want just changing the multiplier... so what's the point of buying faster RAM?)
- FSB * CPU Multiplier = CPU Speed (though mine is listed as 20x, which would be 4GHz, but I have a 3.5GHz chip, so is this the "Turbo" Freq?)

And the HTT and CPU-NB also have their own multipliers.

Yeah this is way more complicated than it used to be, haha. But it should be fun.

 

[trents]

That AMD article in EarthDog's sig is actually really useful for this. What I've figured out so far is:

- Stock FSB speed is "always" 200MHz stock for AMD CPUs

True, except for the AMD APM CPUs which use a 100 mhz bus standard.

- FSB * DRAM Multiplier * 2 = RAM Speed (meaning that yes, you can run any RAM speed you want just changing the multiplier... so what's the point of buying faster RAM?)

Not entirely sure what you're saying here but RAM always has an upper limit at which it will run. You can't run 1600 mhz ram at 2100 mhz but you can run 1600 mhz ram at 1333, 1066, or 800 mhz or anything in between by tweaking the FSB. Running faster ram frequencies can improve performance if and only if the CPU is starved for bandwidth. If it's already getting fed all the data it can handle when the ram is at 1333 mhz then putting in 1600 mhz ram will not likely help much. Then there are also ram latencies (aka, "timings") that come into play here. Lower latencies mean better performance at the same RAM frequency.

- FSB * CPU Multiplier = CPU Speed (though mine is listed as 20x, which would be 4GHz, but I have a 3.5GHz chip, so is this the "Turbo" Freq?)

No, CPU speed is a product of the CPU core speed multiplier (or just "Multiplier") and the FSB. The FSB is also known as the HT Reference. Confusingly enough, in many bioses the FSB is also called the "CPU Frequency". For instance, at the stock FSB of 200 mhz, if you set the core speed multiplier to 15x you get CPU speed of 3000 mhz (3.0 ghz) because 200x15=3000. If you raise the multiplier to 16x you get a CPU speed of 3200 mhz. "Black" edition AMD CPUs have upwardly unlocked multipliers so you can overclock them simply by increasing the multiplier. The easiest way to overclock but not necessarily the best. Non-black AMD CPUs have multipliers that can only be changed downwardly. You can only overclock them by increasing the FSB. Thus, with a non-black CPU that you want to overclock from 3.0 (stock multiplier=15x)to 3.2 ghz you would increase the FSB from 200 to 213 mhz since 15x213=3200.

The FSB is the master system bus. When you change it, it also affects the CPU speed, the ram speed, the CPU/NB speed and the HT Link speed because they are all tuned to it. Each of them has their own adjustments, however, and as you mention below, that must be tweaked in the process in order to keep the system stable.

And the HTT and CPU-NB also have their own multipliers.

Yes, but not "HTT". HT Link is what you meant to say. There is HT Reference (aka, FSB) and there is HT Link. Different parameters.

Yeah this is way more complicated than it used to be, haha. But it should be fun.

Hope this helps.

 

[Cryovenom]

It does help quite a bit.

What I meant by the RAM thing is that originally I was thinking the old-school way where the RAM speed and FSB speed were the same. So if you had PC133 RAM, but your "stock" specs were to run the RAM at 100MHz and your multiplier at 4.5 for a 450MHz CPU like the K6-2 450, you had 33MHz of "room" left to overclock your RAM in order to get more speed. I was trying to figure out how much "room" my 1600MHz RAM had and what speed my stock settings would be at, figuring that the CPU would require my RAM to run at, say 1333MHz and that I'd have 400+ MHz of "room" to overclock into. Now I realize that no, I can always run the RAM I bought at the frequency it's made for, and just adjust the multiplier accordingly.

Still though, when it comes to the CPU multiplier, I'm seeing a multiplier of "20x" here:
http://en.wikipedia.org/wiki/List_of_AMD_FX_microprocessors

But 20x 200MHz = 4GHz, but it's a 3.5GHz Chip with a 4GHz "Half Load Turbo". So is that what my multiplier is adjusting, the "Half Load Turbo"?

 

[ssjwizard]

There are so many things that will effect your OC and our ability to help you out. You did not mention what CPU cooler you are using. We have no idea what PSU you have. How is your case airflow? Your also using a motherboard that has a low rank 4Phase CPU VRM which does not have a heatsink.

You will be able to tweak this system some but dont expect miracles. If your on the stock heatsink I would not even bother OC that CPU.

 

[trents]

Hi Guys,



Now it looks like there's the RAM speed, then the IMC (Integrated Memory Controller?) speed which is different, and then the multiplier, and somehow they end up determining your CPU speed.

What I'm trying to figure out is how much room my 1600MHz RAM gives me for overclocking, and how the RAM speed and the IMC speed relate to each other. What is the "stock" setting for RAM, IMC and Multiplier with this chip, and how does changing one (say, RAM or IMC) affect the others?

I found something saying the IMC runs at 2200MHz, but I can't imagine the system would require 2200MHz capable memory in order to run stock clocks, so what gives?

Jon

Jon, I'm not sure I understand all the technical nuances either about IMC vs. ram speed but I can say some things that might help. First, the memory controller used to be combined with the PCI controller in a motherboard chip called the North Bridge ("NB"). Now the memory controller has been moved onto the CPU die, thus it has been "Integrated". The ICM contains a component that is overclockable (the "CPU/NB") which is a communication bridge, as I understand it, between the CPU cores and the CPU cache and ultimately the RAM. Increasing the CPU/NB frequency increases the efficiency of this communication process and thus enhances overall memory/cache memory performance apart from any change in the ram frequency.

The stock multiplier of your CPU is 17.5x I believe. "Turbo Core" technology speeds up some of the cores under load.

You would do well to download and install three programs: CPU-z, HWMonitor and Prime95 in preparation for your overclock. In particular, CPU-z will show you visually how making changes to one of these components affects the others.

 

[Johan45]

Hi Cryovenom and welcome to OCF
Once you start down this road I'm sure you'll enjoy it. There is alot of help on this forum and some very keen minds.
If you're going to be asking for assistance once you start you should put up a sig that has all the vitals about your rig. This is available at the top of the page under the quick links drop down. You should also download CPU-z, prime95 and HWmonitor(the non pro version).
These are tools we use for diagnosing , testing and monitoring. They offer alot of relative info. You'll be quite familiar with them by the time you're done.

 

[trents]

Gigabyte GA-970A-D3. I wouldn't expect to get much overclock of an 8 core FX CPU with that motherboard. The power phase isn't very rugged and there is no heat sink on the VRM area of the board. Those 8 core FX CPUs draw huge amounts of juice when you begin to overclock them.

And as ssjwizard explained, we need more hardware info. What is the make and model of your CPU cooler, your video card, the make and wattage of your PSU and make and model of your case (+ number of intake and exhaust fans).

 

[Cryovenom]

I'm not expecting miracles with my setup. I'd be happy with even a 5-10% increase and an understanding of how this works so that as I get better parts (cooling, replacement board, etc...) I am comfortable with how the overclocking works and can take it further later.

Mainly I'm looking for the understanding, more than the results. As for my other components, they're modest, listed below (added a Sig as suggested)

Jon

 

[Johan45]

That's good with a stock heatsink and fan you'll be lucky to reach the turbo speed at a sustained oc running prime. Just don't let the temps go over 70 deg for cpu and 60 deg core for an extended period of time.

 

[trents]

Now, open HWMonitor on the desktop and leave it open while you run a 20 minute Prime95 blend test to stress the system and check for max temps. At the end of the stress test, capture an image of HWMonitor and attach it with a post. See note below about how to do that. We need to check max CPU socket temps and core temps at stock frequencies and voltages before we overclock anything and drive temps up higher. We need to see if you have any headroom to overclock from a temp standpoint. If core temps exceed 65c or CPU socket temps exceed 70c, stop the test.

Please attach the image directly to your post, not linked to a webpage. There is a built in forum tool to do this. After you save the pics to disc, click on Go Advanced at the bottom of any new post window. When the advanced post window appears, click on the little paperclip tool at the top. This will load the file browser/uplink tool and the rest will be obvious. You can attach up to three pics per post. If you ever need to add more pics, do so with additional posts.

 

[Cryovenom]

I'll aim to keep it 65/55 under full load if I can. If that means that I only get to go up the smallest of notches, that's fine. It's all about making the most of what you have. If that means I run 3.6GHz instead of 3.5GHz due to cooling and mobo limitations, then so be it. At least it gives me a start, and a damn good reason to start saving up for better coolers/board.

Edit: As soon as I get the system built I'll get the testing done and the results added to the thread. Unfortunately it won't be until this weekend - the g/f and I have made a date of it so we can both upgrade our his/hers gaming rigs before next weekend's LAN. I can handle getting the images in-line, I tend to spend a bunch of time on other forums (like rx7club.com) and have posted plenty of pictorials over there.

In the meantime, it's time to search, search, and search some more!