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Question about AMD Bus Speeds

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May 27, 2002 7:44:11 AM

I thought that the current line of AMD CPUs have a 266Mhz bus but now I am hearing that it is 133Mhz and that they do not want to move up to 166Mhz. Can someone explain and point me to some place that can give me an introduction to modern PC architecture so that I may better understand. Thanks, I look forward to hearing from someone soon.

Poritz
May 27, 2002 7:57:03 AM

No problem. In fact they run at 133Mhz, but memory because its DDR, can transmit information in the raising and the falling of each cycle, doubling in fact the velocity. For this reason they talk about 266Mhz (for memory) and 133Mhz (for FSB).

Now, if AMD FSB moves to 166Mhz, you cuold take more advantage for 333Mhz Memory (166 x 2 because is DDR), because it will work sincro. Currently there are chipsets that support 166/333 (like KT333).

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May 27, 2002 10:31:27 AM

Good explination, you forgot the fact that the system bus itself is also ddr, so thew 133fsb is 266 actual(133x2).

Even if the ram is sdr(single data rate) the athlons bus is still double pumped.

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May 27, 2002 5:02:12 PM

Thanks I appreciate the response. Is there a place where I can read something more indepth?

Poritz
May 27, 2002 7:47:39 PM

Read the name of the website you are at now.
Or head to Anandtech.com

<A HREF="http://www.whatis.com" target="_new">http://www.whatis.com&lt;/A> has a dictionary of all IT words, so you can easily know what you want to know in words.

--
I can't beleive Dungeon Siege has a pitchfork weapon called "Hoe"! :lol: 
May 28, 2002 1:37:37 AM

"HyperTransport devices are designed to operate at multiple clock speeds up to 800 MHz, transferring two bits of data per clock cycle, for an effective transfer rate of 1600 Mb/sec in each direction"

So a really interesting question is at what speed will the CH bus be at. Since the official spec says "UP TO" 800mhz.

Benchmarks are like sex, everybody loves doing it, everybody thinks they are good at it.
May 28, 2002 10:36:41 AM

Thanks Matisaro!

In fact, there is something that I want to know and problably you have the answer. It's correct to say:

a) the information runs at 266Mhz between memory(DDR) and chipset
b) the information runs at 266Mhz between chipset and CPU (AMD Tbird or XP)
c) BUT CPU is clock at 133 times the multiplier.

If this is right, am I wrong assuming the procesor gets twice the information it's clock, but because of the multiplier (making let's say 1.2Ghz) can "absorb" this 266Mhz? So, AMD calculates that the "optimum feeding" for it's processors is 266Mhz?

A little more deeply: if there is a "optimal ratio" between CPU Mhz/FSB Mhz (the one that feed CPU with just the data that can process, nothing more and nothing less) shouldn't be diferent for every CPU? Because a 1.2Ghz CPU can't "assimilate" as many data as a 1.6Ghz CPU, the FSB should be lower than the higher clocked CPU.

I assume that this optimal is just theoric and may change between programs that requieres diferent operations, but seems reasonable. What's more, what is the value of this ratio?

I hope I haven't bored you will all this thinking/meditation.

I have adressed the questin to Matisaro, but obviously anyone is welcome to help me.

Thanks in advance!

DIY: read, buy, test, learn, reward yourself!
May 28, 2002 11:04:32 PM

Quote:
If this is right, am I wrong assuming the procesor gets twice the information it's clock, but because of the multiplier (making let's say 1.2Ghz) can "absorb" this 266Mhz? So, AMD calculates that the "optimum feeding" for it's processors is 266Mhz?


The cpu isnt constantly recieving data(it can be but most times it isnt), the cache plays a large role in what kind of data access the cpu recieves, but your right, the ddr sends data to the cpu via the 266 bus, and sometimes the cpu dosent need data, and other times it needs it faster, its controled by the cpu.

Thats where latency comes in, if the cpu needs data, but its not in its cache, it has to ask the system memory for it, and depending on your setup this can take upto 100ns and during that time the cpu usually is idle, so while a faster bus can be good, a lower latency bus can be good too.

:wink: The Cash Left In My Pocket,The BEST Benchmark :wink:
May 28, 2002 11:04:59 PM

BTW, i took 3 vicadin so my posts may not be coherant right about now.

:wink: The Cash Left In My Pocket,The BEST Benchmark :wink:
May 28, 2002 11:17:16 PM

And I see you hit Forum Fixture, congrats. What's the Vicadin for?

BTW, I was thinking about effective clock speeds a while ago. If clock speed was measured using the effective clock speeds instead of real clock speeds, think of the difference. The P3 wouldn't change, the Athlon's clock speed would double, and the latest P4s would be running at just over 10GHz. That'd make their IPC even lower than it is the traditional way.
Sort of a pointless thought, but something that struck me.

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May 28, 2002 11:20:59 PM

Toothache, woo hoo forum fixture.

:wink: The Cash Left In My Pocket,The BEST Benchmark :wink:
May 29, 2002 7:56:59 AM

Thanks again Matisaro! And no, your post was OK, now I have a little bit more knowledge than before.

DIY: read, buy, test, learn, reward yourself!
!