Can someone demystify FSB mhz and Memory Mhz? 2

[jsteph]

Hi,
I'm a bit confused as to the relationship between the FSB (Front side bus?) and the memory frequency, and System Bus--if that's yet another thing. I had gone into my motherboard's settings and saw that the fsb frequency said 100, and there was a memory frequency % setting, and at 100% it said 'resulting frequency = 600mhz' for the memory. This caused the system to not boot of course, I had to drain the cmos to get it to boot.

The motherboard is a Gigabyte GA7N400-L1. The box says 'FSB 400', but the FSB setting in the cmos only goes to 200mhz. Is this dependant on the processor (I have an AMD athlon 1600)? The memory I got is ddr 2700, which says it's rated at 333hmz, I have it in the dual channel configuration, 2 -256meg sticks. I set the 'optimized' setting for the memory in the cmos, and now when it boots, it says 'Memory frequency 200mhz'. I guess I'm just wondering how to get the most out of this system, so I'd expect it to say 333mhz, but I'm having trouble dialing in the right settings. Can anyone help with this? Thanks,
--jsteph

 

[TheGoatMan]

The speed your thinking of is combined speed. If its a 400 fsb your actual fsb is half that. I'm not sure the exact formula but it works like this. Its the combined bus speed meaning your bus going from your cpu to your memory and from your cpu to your expansion slots. So if its a 400 fsb that means both buses are 200 mhz. And a 333 would be a 166 combined buses make sense? Now I'm sure your chip is a 266. So you probably need to run it at 133 mhz. Try getting a new processor with a 333 fsb. Correct me if I'm wrong but I think thats how it works.

 

[cdogg]

Ok here goes!

First of all you need to understand how the components on the motherboard are connected to one another. There's a decent diagram here:

http://www.extremetech.com/article2/0,3973,1148758,00.asp

The FSB is the path between the CPU and the Northbridge, part of the motherboard chipset (it's divided into two sections - Northbridge and Southbridge). The Northbridge is then connected to RAM known as the memory bus, which runs at its own speed separate from the FSB on newer motherboards (back in the old days, this wasn't so - they had to match back then).

Still with me?

OK. Well the generic term "system bus" can mean a lot of things, but usually they're talking about the entire path from CPU to Northbridge to RAM. This path used to run at one speed. However, with the introduction of faster RAM (like DDR or RDRAM) and FSB speeds, things have changed. Now it's common to see the frontside bus and memory bus running at different speeds, which is why the term "system bus" is not descriptive enough anymore.

In theory, that's bad. Latency (waiting) can occur when the speeds don't match. Think about it. If you are traveling on a 4-lane highway, but halfway to your destination it turns into 2 lanes, then traffic can increase. That's exactly what happens when you run an intensive memory application - not to mention one reason why the P4 never worked out with slower PC-133 SDRAM (but that's another story).

OK, I could write an article spanning several pages, but let's cut to the chase shall we? You're concerned about the settings in your BIOS. Basically, you should have your FSB set to 200MHz. This frequency is "double-pumped" (sends twice as much data per clock cycle) and theoretically is really running at 400MHz (200MHz x 2). The memory bus is also "double-pumped", and I don't believe it should be set to "optimized". Optimized just means that it will avoid latency by causing the FSB to match the memory bus like I talked about earlier. We don't want that since we know they are different. There should be another setting like "auto detect" or 166MHz (166MHz x 2 = 333MHz). If not, report back with the other options that you see. I've also read that with Gigabyte motherboards, hitting CTRL-F1 will let you see advanced settings.

This site may also help you discover the different settings:

http://www.hardcoreware.net/reviews/review-171-3.htm

Sorry for the long narrative, but hopefully you found something useful!



~cdogg
[tab]"The secret to creativity is knowing how to hide your sources"
[tab][tab]- A. Einstein

 

[paparazi]

Is this theory cdogg or practice?
In practice an XP1600+ even though running with PC2700 needs setting to 133/133 default.
The XP1600+ CPU has a 266fsb (133 double pumped by DDR)
Auto will set 133 and will run.
If the CPU was a 333fsb Thorouhbred/Barton then the auto setting would go to 166.
I just know that if I forced set a system with this configuration to the settings suggested it wouldn't post.
But then I might be wrong, it's just when you are building the volume of PC's I do you kinda get to know what does or doesn't work.
As a footnote*
XP2.5+ with PC2700+ 166/166
XP3.2+ with PC3200+ 200/200
All default settings of course.
Martin

Replying helps further our knowledge, without comment leaves us wondering.

 

[jsteph]

cdogg,
Thanks for that narrative! That and the links were excellent resources, I feel alot more clear about what I'm messing with when I'm 'under the hood' tweaking that stuff.
From paparazi's post it looks like I'd do well with an upgraded Athlon chip.
That'll be a good project this morning--a quick run to the tiger warehouse for a new athlon and I should be up and running.

I've never given alot of thought to the memory performance until recently when I started doing a lot of graphics stuff, and I'm staring at huge bottlnecks and stressing my system like it's never been stressed before. Last week I upgraded the mb to this gigabyte unit with the nForce2 chipset--up from a cheap biostar with a quirky via chipset. That alone (using the same cpu) made a noticable difference. Now with an upgraded athlon--where I'll be able to utilize all of the ddr's capability--I should get even more.

Thanks again, and I'll let you know how it works out,
--jsteph

 

[cdogg]

jsteph
Glad to hear it! Good luck and let us know how it turns out!

paparazi
Damn your good! You caught me again...I completely overlooked the fact that we were talking about an older Athlon.

By the way, can't you offset the memory and FSB manually? I was under the impression that you could set the memory bus to 166MHz while leaving the FSB to 133MHz? In the end, it would be better just to upgrade the Athlon, but just curious at this point...


~cdogg
[tab]"The secret to creativity is knowing how to hide your sources"
[tab][tab]- A. Einstein

 

[jsteph]

Well, I ended up getting the Athlon XP 2500+. I guess this is late to be asking, but is the Barton core better than the Thoroughbred core? This has the Barton core, and its actual speed is only just over 1100 mhz, whereas my old chip was just an 'Athlon', without the 'XP', but it was 1005 mhz actual.

I was able to set the fsb to 200mhz (it still only has a max of 300mhz), and setting the memory divider to 83% gives 166mhz, which, from what I understand, is doubled via ddr, and gives 333mh memory frequency, which is what the boot screen now says.

The performance is noticeably better of course, though not eye-popping. But to me, although I gain a real-world benefit to the added performance, most of it's just the fun putting it together and tinkering. Having the the warehouse nearby is both a blessing and a curse, I can't walk into that place without spending money. Well, my kids benefit because they get the systems built from all my old parts. That's the excuse I tell my wife, anyway.

The one thing I can't get to work is the EasyTune 4 overclocking utility--Gigabyte say's it's currently incompatible with the nForce2 chipset. Are there any third-party Windows clocking utilities out there, or am I stuck with rebooting and going into cmos each time?
Thanks for all your help,
--jsteph

 

[xomcat]

I can only answer your first question. The L2 cache in a Barton is a definite + in gaming and other graphic intensive apps.

 

[jsteph]

Oooops--forgot to flip the clock switch--Ok, NOW it's eye-popping! When I started looking at the 1100mhz of this new processor, I thought it was a bit low for going from a 1600 to an XP 2500+, so I went and RTFM, and the Gigabyte manual said that for the faster cpu's, I should flip the clock switch on the motherboard...I guess I just wanted to pop that thing in and go.

I'd left my settings at the 200mhz system bus--and now when I booted up it said 'Athlon XP 3200+'. Whoa!! I'm likin' this. The mhz in Windows now says 2200mhz. That's more like it. My graphics app that was the instigator of this whole upgrade is popping back and forth like it's alive now! I'll watch the stability, this being only the althon xp 2500+, but it sure is nice to be able to have the extra juice. Thanks again,
--Jsteph

 

[jsteph]

...and to explain my original confusion--that Clock Switch, as explained by Gigabyte, locks the system bus at 100mhz, regardless of what you try to set the cmos settings to, which is why I saw the 200mhz (doubled 100mhz) for the memory frequency initially--regardless of what I set the cmos to.
--jsteph

 

[paparazi]

Barton core XP's have double the level 2 cache when compared to Thoroughbred core models (512 instead of 256) so are definately the ones to buy.
Default front side bus setting on your XP2.5+ is 166 and not 200 so you are effectively (overclocking!) so be warned!!!!, you could easily fry your CPU.
Easy Tune 4 does work with Nforce2 motherboards (I have Gigabytes GA7-NNXP) and it works fine but only after a bios flash to a later version than factory.
Flashing the bios on your board is an absolute doddle as the flash utility is built into the bios itself, once into the bios screen press F8 to enter, you just need the new bios bin file on a floppy (download from Gigabyte) making sure you get the exact flash required.
Martin


Replying helps further our knowledge, without comment leaves us wondering.

 

[cdogg]

Yes, leave your FSB setting at 166MHz, since your CPU and RAM are meant to run at 333MHz not 400MHz.

Sounds like a kickin' system...