Totally confused about KT133A and FSB's !

[MikeO]

So, I've read that the KT133A is basically the same chip that KT133, but adds 133mhz fsb support, for the newer 133 fsb Athlons.

BUT, I already have the "older type" 100mhz fsb Athlon and I am currently seeking for a new mobo. What are my advantages if I buy KT133A based board? I'm totally confused about this fsb thingie If I put my 100mhz fsb Athlon to a 133mhz fsb mobo, does my processor start to run at 133mhz (or maybe even above if overclocked??). Or what?

I did read that one advantage (or the only?) would be, that if my processor starts to run at 133mhz fsb, I would be able to lower the multiplier, still remaining at the same clock speed, but still gain some performace.. eh..

If someone would please explain this to me, so even I could understand it (so please, keep it simple!) thanks

 

[randomlinh]

you gain the ability to run at 133mhz FSB.. so yes, you can lower the multiplier and run at the same speed... assuming the cpu is unlocked.

OR.. you could try running the processor at the 133 FSB.. and overclockt he crap out of the CPU

your processor will default to the 100mhz bus.

 

[Informant X]

First off the old KT133 chipset mobo's while saying they support FSB's up to 133, they don't. You'd be lucky if you can get to 115mhz FSB. The KT133A now officially supports 133 mhz bus speeds and above. Which is good. They also have onboard RAID, most of'em anyway.

Now to obtain a processors MHZ you do the "FSB X MULTIPLYER = Speed" So if you have a have 900mhz althon, it would be "100 X 9 = 900" at default speed. (FSB means Front Side Bus Speed)

Another note is that most of the Thunderbirds out there now will do 133 FSB. You might have to drop the multiplyer a little but that's no big deal. You'll notice a much larger perfomance increase by overclocking with the FSB as opposed to just Multiplyer. All the new KT133A chipsets that support the 133 Althons (soon to come out) are backwards compatible with the older 100 FSB ones. You just select the proper speed in the bios, or by jumpers on the motherboard. Essentially the new 133 althons will be the same as the thunderbirds out now, but they'll just be able to handle a higher fsb.

 

[TGirl]

I'm totally confused on this. I have the MSI pro2a with a 1G Athlon. Right now I have it set to 100 x 10. How would I set it up to take advantage of the 200 supposed fsb. My choices are 100 or 132 and there is a blank to enter this in the bios. How should I set this up to take full advantage of the bus without actually ocing my processor (warranty)?

Thanks

TGirl

 

[Octoberblue]

TGirl:

The "200Mhz Frontside Bus" advertised with the KT133 boards is really what you are already running. Your actual frontside bus speed is 100Mhz, but your Athlon or Duron processor is internally performing "DDR", which is to say it's doing Double Data Rate, pumping data twice per each cycle. They call this the "rising" and "falling" "edges" of the clock cycle. This results in an effective frontside bus speed of 200Mhz.

The new KT-133A boards provide actual frontside bus of 133Mhz which, also "double-pumped" by your processor results in an "effective" frontside bus speed of 266Mhz. The whole "effective" thing just means that your bus actually has the same bandwidth that it would if it were running 200 or, in the KT-133A, 266Mhz.

Your best configuration is to set your frontside bus speed to about 115Mhz. It will probably crash your system or not boot, but if it's stable you'll be going much faster. If it crashes go down to 114, 112, etc, until you find a stable bus speed. Your processor will be slightly overclocked by this, but it almost certainly will be able to easily handle this.

 

[Octoberblue]

Actually since you have an MSI board I believe they have a program that can overclock your frontside bus from within windows. Not sure what results people are getting with it, but it sounds great in theory. Apparently it runs your frontside bus speed up from within windows until the system becomes unstable, which it detects, then automatically lowers it again until everything is perfectly stable. About as easy as you can get if it works well. Anybody remember the name of that?

bump

 

[Octoberblue]

bump

 

[TGirl]

Is it the Fuzzy logic III your talking about? So you guys are saying that only the processor bus runs at 200? I thought I read that with the newer bios you could run your system bus at 110 instead of 100. I'm totally new at this and am trying to use this system as a learning tool but I don't want to void the warranty on my Athlon, either. Would it be best to do this through Fuzzy logic. I'm pretty nervous about this as I've already had to buy a new bios from badflash.com because I fried the bios chip running livebios. There are lots of us who did this. FYI, if you must flash the bios, do it thru dos!

Thanks for the tips, all.

TGirl

 

[Peter]

Let's put this all straight.

(1) the CPU bus. It runs at 100 MHz on KT133, and at 100 or 133 MHz on KT133A. The DDR (double data rate) method used makes many people talk about 200 MHz or 266 MHz bus, which it isn't. It's just that effective throughput on a DDR bus is about what you'd get with an SDR bus at twice the clock rate.

(2) the SDRAM bus. On either chipset, when the CPU bus is at 100 MHz, the SDRAM can be run at 100 or 133 MHz. With KT133A and the CPU bus at 133, SDRAM has to be 133 too - KT133A does not have an "SDRAM slower than CPU" bus mode.

So, your choices are 100/100, 100/133 and (KT133A only) 133/133. This means you can run today's 100 MHz bus Athlons on KT133A as well.

Regards, Peter

 

[Octoberblue]

It may be Fuzzy Logic III. If I were you I'd post a thread asking about Fuzzy Logic III. See what kinds of results people are getting with it. If it is at all problematic, just set your fsb speed in the BIOS. If their livebios software fried the bios chip I'm not sure how much I'd trust their overclocking software w/o lots of positive confirmation from other users. Since you've heard 110 is the best setting, give that a try.

Don't worry about your Athlon warranty. Raising the fsb by 10 or 12 shouldn't harm you chip at all. The things that usually harm a chip are 1)Poor connection of the core with heatsink and 2)Raising the voltage too high during extreme overclocking. If you don't raise the voltage, just push up the frontside bus, you almost certainly won't hurt your Athlon. If your attempt is unsuccessful your system will crash or not boot fully into windows until you change the fsb back, but this just means your system can't go that fast, not that it's in danger of being fried or anything.

 

[TungFree]

Tgirl got good clear explanation and advice...

Tungfree

 

[DaddyG]

I see Peter is yet another who mixes up the 'clock' and the 'Bus'. The EV6 BUS is infact 200mhz. The data are 'clocked' onto the Bus using the leading and trailing edge of the clock, BUT the BUS runs at 200 mhz.

 

[Cooltech2k]

Yea I took my Tbird 900 from an a7v running @ 900 & knocked it up to 1035 when I upgraded to a kt7a-raid by moving my FSB to places it would never go before..... Even when I adjusted the multiplier in my A7V the best My TBird would ever go was 1050 with a 10.5 multiplier. That is pretty close seeing as how I havent touched the multiplier in the NEW Board
...

 

[EddieGee]

What the hell is going on here. I don't think anyone really knows what is going on with an Athlon - bring back pentium?

I have an Athlon gig running on a KT7RAID board. The multiplier is set to 100 and the FSB to 100/33 - I can't get anymore than that without going into user define. That I have done and it crashed big style when set to 133/44

My question is if the FSB is physically set to 100 how the hell can you get 200 out of it or even maximise the effect of 133 memory? I have 133 memory, but is a 100FSB really using it? Why bring out 133 compiant Athlons if it does and more to the point 133 speed MB's.

Think we need input from AMD cause this is smelling decidely like BS.

 

[MCS]

You need to select 133/33 not 133/44 for starters...

 

[MikeO]

Hehe, there seems to be lots of others confused about this
Gladly, I now finally begin to understand this. Except the PCI
bus' relation to all of this. Do I have worry about the PCI bus
when overclocking? Can I push it too high and hurt it?

One additional question, does the KT133A boards run 100 or
133mhz fsb at default? Or does it depend on the processor you put
on it?

Thanks for all input and help!

 

[MCS]

Your PCI divider is set at 1/3 until you reach a FSB of 124 (I think).

After that, its set at 1/4.

So at 100 and 133 FSB your PCI is set at default of 33Mhz.

You want to keep your PCI bus at 37.5Mhz or under, unless you have exceptional componants.

 

[Octoberblue]

Okay, okay, it is confusing partly because the technical definitions are slightly different from the normal conversational use of the terms. Before the Athlon came along there was no difference in the clock on the frontside bus and the frontside bus speed itself, so no one is used to distinguishing the two.

But you have to with the Athlon just like you have to with DDR memory. Everyone is pretty hyped about DDR RAM, but the Athlon is misunderstood thought it uses the same (or a very similar) process. Athlon systems do take full advantage of 133 memory. The memory bus runs at 133, and there are no bottlenecks before it or after it to hinder getting the full bandwidth benefits of PC 133 CAS-2 memory.

The "clock" (as Daddy G points out) is set at 100MHz to the frontside bus. The Athlon/Durons load up data twice per every clock cycle, unlike the PIIIs which only load it up once every clock cycle. So the Athlon gets 200MHz worth of "stuff" loaded onto it, and the bus itself, which is almost a figure of speech at this point, is running at 200MHz. This allows the throughput of data to be plenty fast enough to take full advantage of the PC-133 memory, and even more so with the 133A chipset and it's 133 clock speed resulting in a 266 frontside bus speed.

The PCI bus will definately not be you limitation on the KT133 boards, and probably not on the KT133A's either. You would think with this 266 bus speed the Athlon would be able to take full advantage of DDR memory as well, but it, like the PIII cannot.

 

[Peter]

DaddyG,

nice try. Try again.

The FSB clock is 100 MHz (or 133), and the data lines are allowed to change at the rising and falling edge of the clock signal. Hence, just like a 100 MHz clock signal, where rising edges are 10 nanoseconds apart so that a state change appears every 5 ns, the data lines may change state every 5 ns. That's the idea behind DDR.

So one does have a 100 MHz operating frequency on the bus (ain't no mixing up here, busses have operating frequencies, don't they?), with the data pump rate doubled. No 200 MHz frequency anywhere on the mainboard. The bus is 100 or 133 MHz, as can easily be seen from the diagrams in AMD's data sheets. The difference from a true 200/266 MHz bus lies in the non-data phases where no DDR is used - these are just as fast as on an SDR 100/133 MHz bus. EV6 is 100 MHz DDR, not 200 MHz.

So anyway, even with 100 MHz CPU bus, you get an effective pump rate that would make good use of 200 MHz SDRAM - your PC133 stuff is well saturated with that.

As for PCI bus frequency ... most clock synthesizers that are available right now switch to PCI = CPU/4 scheme at 124 MHz, below that it's CPU/3.

The "default" frequency is set by choice of processor. Put a 100 MHz type in and you'll get 100, with the new 133 MHz Athlons you get 133.

Regards, Peter

 

[DaddyG]

Peter, incorrect. The data frequency is 200mhz. Look at the data with a scope, you will see absolutely zero difference between the data on a 100mhz DDR clocked BUS and a 200mhz SDR clocked bus. The way the data is clocked onto the bus is of little consequence.

A BUS is controlled by a clock, not a 'operating frequency' makes zero diff what part of the clock is used.

 

[DaddyG]

Oops double dip sorry

 

[Peter]

Hello? That's exactly what I said - on a DDR bus, the DATA move along at TWICE the clock speed, but the non-data activities (like address phases) are done at non-doubled clock speed. A true 200 MHz bus would give lower latencies than a 100 MHz DDR bus for exactly that reason.

So if you have the equipment, then go compare the PROTOCOL on SDR and DDR 100 MHz busses, and you'll see no difference.

I'd also like you to explain the difference between frequency and clock speed.

Peter

 

[Neos]

Does this mean that if I get my MSI Pro 2 (not A)to 120 FSB ..the PCI bus will be 40, but if I get it to 133 (impossible, I am sure) then it would be 33 ...(which is ideal)
Right now I have my Duron 650 @ 856 (107*8. I had it at 108*8 @ 1.65v. ..it done fine, but actually went down in some benchmarks, so I went back to 107.
I have the hope to go higher, but as yet have not tried higher than 1.70v. ..so it may be that I have a lot more room as I can go to 1.85v.
I am concerned about getting the FSB too high, though.
Neos

 

[Octoberblue]

Yeah, it would be 40. That's a little high for some things, but if you're just using the "bare essentials", a modem, video card, & sound card, if they are high quality they should be able to take 40.

I don't think there's any way it'll go up that high to be honest with you. Let me know if I'm wrong, but if you got it up to 112 or 115 you'd be doing better than normal. Does your chipset have a hsf on it? Does it have thermal compound? If not you could add thermal grease and a fan from radio shack & maybe it would go up. Let us know how it goes!

 

[DaddyG]

Peter, I agree that 'potential' differences exist on non-data operations. Latency is a complex issue, which has little effect on the actual operation of the EV6 BUS. The EV6 bus can handle 4 times the number of outstanding requests as compared to GTL+ on the Intel platform, so actual latency is minimized.

There is a big difference between Clock and Data Frequency. A BUS can be clocked by any part of a clock signal, or any derived part of a clock signal. Leading edge, trailing edge, delayed leading edge, doesn't matter. Consider, if you will, the various methods used by modems to modulate a basic carrier signal to achieve high transfer rates.