newbie questions

[Guest]

Hi,

I decided to assemble my first pc and decided on a Athlon 1.4 GHz cpu. My questions:

(1) AMD shows their cpus as 200 or 266 FSB whereas the reiews here on tom's hardware list them as say "Athlon 1.2 GHz 133 FSB" and in one article mention 2 types of Athlon 1.4 GHz sb-type 100/200 and c-type 133/266 .FSB is the speed which with the processor talks to the memory(RAM) right? so why does the company say it is 200 (or 266) and the erviews say it as 100/200( or 133/266)

(2) AMD lists the prices of the 1.4GHz cpu as $253 but some companies on pricewatch list them at around $110 . how come so cheap? am i missing something?

thanks
sundar

 

[FatBurger]

1) b=100=200
c=133=266

2) Nope, you're not missing anything. $107 is the current cheapest price on PriceWatch for a 1.4/266.



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[Guest]

front side bus depends on the motherboard

 

[FatBurger]

What? Explain yourself, please.



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[Guest]

>b=100=200
>c=133=266
thats my question.... why do you use both 100 and 200? isn't the speed between the processor and the memory either 100 or 200? how can it be both?

 

[atavus]

It's 100 mhz, but it's double pumped to make it run at 200 mhz. Kind of like DDR Ram.

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[FatBurger]

Ok, both the CPU and the memory are controlled by what's called the Northbridge. Wait, bad starting point. I'll get back to that, though.

The 100 or 133MHz comes from the AC current flowing across the motherboard. It goes at 100 or 133 million times a second. Now, it's not so much on/off as it is a wave, flowing up and down, with peaks and valleys and slopes in between. Make sense? That AC current is knows as the Front Side Bus.

When the Athlon came out, they decided that instead of having it execute (send/recieve info) ONCE every clock cycle (or 100/133 million times a second), it would execute on the rising and falling edges of the clock. Remember the AC wave? Good.

That's where the 200/266 comes from. The AC current isn't flowing across the motherboard any faster, the CPU is just requesting/sending information twice as much as before (twice as often in the same amount of time).

Now, with normal SDRAM, it runs at the same 100/133 MHZ. DDR runs at 200/266 in exactly the same way the Athlon does, rising and falling edges of the clock. Twice as often in the same amount of time.

It's sort of like if you're sawing a tree with a two-man saw. You saw one way, lift the saw away from the tree, move it back, and then saw back the first way. Then, you realize you can actually saw both ways, and even though you move it at the same speed and the same number of times, you're getting twice as much done. Got it?



Now, your PCI and AGP slots (and ISA and VLB and...), all run at a fraction of the Front Side Bus (FSB). With some motherboards you can change that fraction. So with a 100 FSB, your PCI slots are running at 1/3 of that, or 33MHz. At a 133 FSB, your PCI slots are bumped down to 1/4, but still 33MHz. 1/3 of 100 is 33, 1/4 of 133 is 33.
The AGP bus runs at a different fraction of that, the exact amount of which escapes me. Let's move on.

Back to the Northbridge. When the CPU asks for a certain piece of data, it doesn't go straight to the banks of RAM. Hell, no. It goes through the Northbridge. The Northbridge controls the CPU, RAM and AGP slot. So when a Tbird runs at 266, it's talking to the Northbridge at 266, whereas the RAM might only be running at 133.


That's why, when someone says that a CPU has a 266 bus, it's really a 133 bus. The CPU is running at 266, but the bus speed across the motherboard is really 133. It's called a double-pumped bus. The CPU is running double the FSB.

The P4/RDRAM platform went a step further and it executes 4 times each clock cycle. That's called a quad-pumped bus.



I'm gonna stop. Feel free to ask any questions, but I'm off work in 25 minutes, so I probably won't get back to you.



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[Flyboy]

AC current? I thought it uses DC. I thought all power on the motherboard is DC. That's why all of the connectors from the power supply are 5V or 12V DC. AC is what goes into the power supply, i.e. 120Vac.



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[Era]

I thought it was 220Vac.

 

[74merc]

yer right, its DC current, but for the sake of the explanation... close enough.

Era, it depends on where you are, we use 110-120v AC in the US, seems most other places use 220v.

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[Arbee]

AFAIK the different operating frequencies are set by crystals (clock generators), not from AC current flowing in the MB .
Although there are different dividers for PCI (1, 2, 3, 4 and hopefully 5 in a near future) and AGP (1, 3/2, 2 and hopefully 5/2 in a near future) I'm not sure if ISA isn't always set to 8Mhz (8/16bit). Not that it is of any importance anymore.

That's why, when someone says that a CPU has a 266 bus, it's really a 133 bus. The CPU is running at 266, but the bus speed across the motherboard is really 133. It's called a double-pumped bus. The CPU is running double the FSB.

This is misleading as the CPU is not running at 266Mhz - I see what you mean, but IMHO you made an unfortunate choice of words.
<font color=blue>The FSB is the connection between the CPU and the memory controler </font color=blue> (usually part of the northbridge). The CPU operating frequency is set through a multiplier of the FSB true operating frequency - and nowadays this multiplier is quite above 2.
Also, if the chipset is limited to syncronous memory (such as AMD chipsets), then the memory modules operating frequency must equal the FSB frequency.

In a way, the FSB <font color=blue>true</font color=blue> operating frequency sets the pace of the entire system:
CPU - through cpu multiplier (usualy from 8x to 14x)
PCI - through PCI divider (3 or 4)
AGP - through AGP divider (2/3 or 2)
RAM - FSB frequency (syncronous) or FSB +- PCI (VIA chipsets)

So, as an example: the northbridge sends 2.1GB/s of data to the 1.4Ghz CPU (10.5 multiplier) though a double pumped 133Mhz FSB (EV6 bus protocol) and retrieves data from memory @ 1.06 GB/s (133Mhz SDRAM). The (southbridge) PCI bus operates @ 33Mhz (1/4 of FSB) and AGP @ 66Mhz (1/2 of FSB). This is an example of a 1.4Ghz Tbird on a KT133A based mobo.


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[FatBurger]

Geez, you guys always gotta pick apart everything I say. Everything in there was perfectly accurate, but here you are talking about how it's not quite right and confusing anyone who stumbles across this.

Oh well, I guess I'll just stop trying.



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[Matisaro]

"Also, if the chipset is limited to syncronous memory (such as AMD chipsets), then the memory modules operating frequency must equal the FSB frequency."

amd chipsets do not require syncronous memory frequencies.(kt133, kt133a(some mobos have fsb+pci for ram((166mhz ram)) etc.



~Matisaro~
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[Arbee]

he he he - to be fair, most of my ranting wasn't targeted at you, specially the "example" part (you're probably more than aware of that info).
Nevertheless, the "CPU works at double that speed" part isn't correct.



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[Arbee]

AFAIK the KT133 and KT133A are VIA chipsets, not AMD.



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[FatBurger]

No, but the CPU is running at a 266 bus speed, which I think was clear enough.

And I he meant AMD platforms not actual AMD chipsets.



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[Arbee]

Guess it was

And I think in my post it is quite clear that AMD chipsets refer to actual AMD chipsets and not chipsets for AMD CPUs (otherwise why would I refer the VIA chipsets? due to the "very" common C3 processors?)

BTW it is really time to change the sig of the week. Unless they mean it to be the sig of the year :lol:

How terrible is wisdom when it brings no profit to the wise

 

[FatBurger]

No, in your original post it wasn't clear at all. It easily could have meant chipsets made for AMD CPUs. But doesn't matter. As long as we know what you mean now.



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[Flyboy]

My post wasn't meant to "pick apart" your post. I know what your saying, AC or DC really won't make a difference regarding his question about bus speed. Nevertheless, with the exception of grammatical and spelling errors (has nothing to do with hardware), then I feel all mistakes/errors should be pointed out. You never know where a person may use your information, like an interview or just explaining it to someone else. So to me it pays to be as thorough and accurate as possible.

And even so, if you didn't know that it was DC, I thought I was helping ya' out.

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[FatBurger]

No, you're absolutely correct. Sort of. All the power to the motherboard and to the hard drives, CD-ROMs, etc. is DC. However, the FSB is an AC current, otherwise it could only go one way. E.g. the CPU could receive information but not send it out.

But you're correct, all power coming out of the power supply is DC. The motherboard converts it back to AC to a certain extent.



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[Flyboy]

Hmmm. I never thought of it that way. I thought it was a DC voltage and current that was bidirectional. I Figured it uses a "Write" or "Read" bit to set the direction to write or read from RAM, but is still DC. You might be right. I guess I don't know what to believe. Guess I need to start digging! Maybe I'll post the answer in a new thread.

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[Raystonn]

"the FSB is an AC current, otherwise it could only go one way. E.g. the CPU could receive information but not send it out."

Sorry, the electrical characterists of the component, such as the type of voltage used, has nothing to do with the bit signalling or logic. Electrons don't hold the information, and if they did they would go nowhere with AC current. (AC current switches the direction of the electrons 60 times per second [60Hz], essentially keeping the electrons in the same general area bouncing back and forth.)

All components (with the exception of the PSU that does the conversion of course) in your system use DC only. Information is transmitted by making certain wires 'hot' (applying current to them). The other side sees it is active and counts that as a 1. A cold wire is counted as a 0. This is done millions of times per second. A clock (via some crystal) is used to synchronize the signals so the components know when to look at the voltage on the wires and the sending side knows how long to keep applying the current.

Note: This is where the CAS setting on RAM comes into play. For slower RAM, you must set CAS to 3. This causes system to apply current to the frontside bus for 3 additional clocks instead of just 2. It ensures the signal is present on the wires long enough for the memory system to see it and properly read it.

-Raystonn


= The views stated herein are my personal views, and not necessarily the views of my employer. =

 

[FatBurger]

Of course, it's 55Hz in a lot of places in the world. Only America and the (North?) half of Japan is 60Hz, I believe.



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[Era]

AC current?I tought it uses DC.

Gee,I'm sorry.I thought you were just trying to be funny.