AMD and FSB

dreamtfk

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Feb 1, 2002

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Orlando FL

• Feb 9, 2006

• #1

I've been doing some window shopping of AMD cpu's for sale and have been looking for the FSB speed on the X2's but haven't seen it listed. Does the X2 architecture not use FSB? I would appreciate it if someone could explain this to me...

 

Know Nuttin

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Mar 25, 2004

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Ontario, Canada

• Feb 9, 2006

• #2

Not really FSB per se. Most definitions of FSB include memory access by the CPU. Athlon64 has its own channel to memory not through the motherboard chipset so in essence, it does not have "FSB".

Athlon64's communicate to the chipset using the HT bus. It's a point to point bus, full duplex. Memory access is not part of this.

Pentium 4's use an FSB, and all traffic flows through it to the CPU. Memory access, information from the hard drives, even data from another CPU core, will travel through the FSB.

 

princeofdarknes

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MS, The redneck south -.-

• Feb 9, 2006

• #3

I'm pretty sure all A64's have a base HTT (basically the FSB) of 200 with the LDT (HT multi) being 4x or 5x (800 or 1000)
I may be wrong, so dont take my word full heartedly for this
-prince

 

H

hookem2oo7

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Jan 22, 2006

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Austin, TX

• Feb 9, 2006

• #4

I've seen it advertised as a 2000mhz FSB, but i cant find the logic in that number

 

Shelnutt2

Overclockers Team Content Editor

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• Feb 9, 2006

• #5

hookem2oo7 said:

I've seen it advertised as a 2000mhz FSB, but i cant find the logic in that number

Click to expand...

I second that

 

IWasHungry

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Oct 18, 2004

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Seattle, WA

• Feb 9, 2006

• #6

200MHz FSB is the base for all AMD CPUs starting from late Socket A until today.

 

G

Gautam

Senior Benchmark Addict

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• Feb 9, 2006

• #7

The closest thing that an A64 has to an FSB is its HyperTransport bus. It carries the data from the PCI bus, one of the functions of the traditional FSB. That's the logic behind them being advertised as having 2000MHz "FSB's," albeit a loose one.

Not to be confused with the HTT, aka reference clock, aka external clock, which is at 200MHz. Architecturally, it couldn't be any less similar to an FSB.

 

brakezone

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Joined

Jan 3, 2004

• Feb 9, 2006

• #8

Yeah,

In my A+ hardware class the teacher said a pentium 4 at 3.2ghz has a FSB of 800mhz... so then he said that meant it had a multiplier of 4. The lesson to be learned here is that there is a difference between technical wording and the wording people use to sell things. P4 3.2ghz cpu multi would probably be more like 16 with a 200mhz fsb and a 800mhz databus. On the amd size the HTT X cpu multi= cpu speeed, hypertransport bus = HTT X LTD (hypertransport bus multi). On the Socket A, I think the FSB is 200 and the databus is 400 (ddR).

 

OP

dreamtfk

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Feb 1, 2002

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Orlando FL

• Feb 9, 2006

• Thread Starter
• #9

So is this HT that the Athlon64 uses more efficient than the FSB that the p4 uses?

 

princeofdarknes

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MS, The redneck south -.-

• Feb 9, 2006

• #10

the reason why you see 2000mhz is because in that case its 1000mhz both ways(200mhz HTTx5), that's why you sometimes see 1600mhz for 800mhz both ways (200mhz HTTx4)
There's accually up to 16bit both ways, to the chipset and back to the cpu. Does that clear up anything?
But there's nearly NO performance loss between 2x and 5x, maybe 1 frame or two ingame max

 

Know Nuttin

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Ontario, Canada

• Feb 9, 2006

• #11

dreamtfk said:

So is this HT that the Athlon64 uses more efficient than the FSB that the p4 uses?

Click to expand...

Yes, as it doesn't have as much data to carry across it at the same time. Data from memory to CPU is not going over the HT bus. That is a huge thing.

Also, the HT bus is full duplex, so it can send/receive data at the same time. The P4 uses a half duplex bus, so data can only go one way at a time.

 

Know Nuttin

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• Feb 10, 2006

• #12

_damien_ said:

The way I see it, the HyperTransport bus only replaces the more traditional Hub Interface (linking the SB to the NB). For that reason it seems inaccurate to compare the HT to the FSB.

Click to expand...

to the forums.

True for some chipsets but the favourite chipset for AMD is the nvidia nforce4 series, and they don't have a southbridge chip. So the HT bus is between CPU and the nforce4 chipset.

The interface between the IMC and the CPU run at the same speed as the CPU.