The HyperTransport Bus of the Athlon 64

**Hardware Secrets Team** · 12-02-2004, 04:02 PM

There has been a new article posted.

Title: The HyperTransport Bus of the Athlon 64
URL: http://www.hardwaresecrets.com/article.php?id=19

Here's a snippet:
One of the main differences between the Athlon 64 and 64 FX processors and all the other processors in the market today is that they have an internal circuit called memory controller. In the other processors there is no such circuit, and it is the chipset of the motherboard (more specifically, a circuit called north bridge) that performs the communication ...

Comments on this article are welcome.

gonar · 02-14-2006, 06:11 AM

<quote>The HyperTransport bus works at 3,200 MB/s in each direction (as it was explained, this bus uses one transmission path independent from the reception path) and that is why it is listed as being a 6,400 MB/s bus, which is not true and is one of the main misunderstandings published in the market. In brief, it is as if we said that a highway has a speed limit of 130 MPH just because there is a speed limit of 65 MPH in each direction.</quote>

you are making the common mistake of confusing "speed" aka "latency" with "throughput". their statement is absolutely true, you are just misunderstanding what they are saying.

to take your mixed metaphore to it's rediculous extreme, you are effectively saying "a 1 lane 1 way street with a 65 MPH speedlimit is just as fast as an 8 lane 2 way superhighway with a 65 MPH speedlimit"

yes, it's just as fast, FOR ONE CAR. but if you have any traffic at all, or any need for bi-directional traffic, the one lane road is not useful.

to put it back in computer terms, on an empty bus, the time (latency) to transmit one packet of data in one direction is the same between the both the unidirectional and bi-directional bus, but the maximum bi-directional throughput differs greatly.

their max throughput numbers are absolutely correct.

tygrus · 09-05-2007, 06:30 PM

Quote:

http://www.hpcwire.com/hpcwire/hpcwi...22/108614.html
“We will be implementing HyperTransport 2.0 technology in a range of AMD Opteron and AMD Athlon 64 processors, starting with the AMD Athlon 64 processors 3000+ and 3200+, which are available today."October 22, 2004

The first 1000MHz HT was a 1.0# (1.03 or 1.05) revision. From October 2004, AMD started shipping parts compatible with the HT2.0 spec at the lower 1000MHz speed (instead of 1400MHz which required additional electronics to filter and compensate).
Documentation from AMD and the HyperTransport consortium doesn't provide enough detail of the transistion to the HT2.0 spec. The marketing & PR department didn't think it mattered when you just hype the GB/s.

* Nvidia nForce5 chipset;
* ServerWorks HT-2000 HyperTransport™ SystemI/O™ Controller from Broadcom Corporation;
* SiS756 HyperTransport to PCI-E/MuTIOL North Bridge;
* AMD-8132™ HyperTransport™ PCI-X® 2.0 Tunnel from AMD;
And many others use the HT2.0 spec.

From the Wiki

Quote:

HyperTransport is used, with a speed of 800 MHz (Socket 754, one OEM-only Socket 939, older Socket 940, Socket S1, Socket AM2 Semprons) or 1 GHz (almost all Socket 939, newer Socket 940, Socket AM2 Athlons).

**Gabriel Torres** · 09-07-2007, 07:08 AM

Hi there,

Yes, I made a huge mistake stating that AMD processors don't use HT2. I will fix this ASAP. I am studying more about this stuff. Please hold on. And thanks a lot for pointing this out to me.

Cheers,
Gabriel.

**Gabriel Torres** · 09-19-2007, 07:25 AM

Just to let you guys know that I've just updated our HyperTransport tutorial correcting some mistakes I wrote. Basically, I've said HyperTransport 2.0 was never used on AMD CPUs, which is quite wrong -- all current AMD CPUs are based on HT2 using, however, the lower speed grade provided by this version of HyperTransport. It is just that AMD does not say anything about the HyperTransport version they use on their datasheets, what got me confused.

12-02-2004, 04:02 PM	#1
Hardware Secrets Team Administrator Join Date: Nov 2004 Posts: 2,952	The HyperTransport Bus of the Athlon 64 There has been a new article posted. Title: The HyperTransport Bus of the Athlon 64 URL: http://www.hardwaresecrets.com/article.php?id=19 Here's a snippet: One of the main differences between the Athlon 64 and 64 FX processors and all the other processors in the market today is that they have an internal circuit called memory controller. In the other processors there is no such circuit, and it is the chipset of the motherboard (more specifically, a circuit called north bridge) that performs the communication ... Comments on this article are welcome.

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02-14-2006, 06:11 AM	#2
gonar Junior Member Join Date: Feb 2006 Posts: 1	<quote>The HyperTransport bus works at 3,200 MB/s in each direction (as it was explained, this bus uses one transmission path independent from the reception path) and that is why it is listed as being a 6,400 MB/s bus, which is not true and is one of the main misunderstandings published in the market. In brief, it is as if we said that a highway has a speed limit of 130 MPH just because there is a speed limit of 65 MPH in each direction.</quote> you are making the common mistake of confusing "speed" aka "latency" with "throughput". their statement is absolutely true, you are just misunderstanding what they are saying. to take your mixed metaphore to it's rediculous extreme, you are effectively saying "a 1 lane 1 way street with a 65 MPH speedlimit is just as fast as an 8 lane 2 way superhighway with a 65 MPH speedlimit" yes, it's just as fast, FOR ONE CAR. but if you have any traffic at all, or any need for bi-directional traffic, the one lane road is not useful. to put it back in computer terms, on an empty bus, the time (latency) to transmit one packet of data in one direction is the same between the both the unidirectional and bi-directional bus, but the maximum bi-directional throughput differs greatly. their max throughput numbers are absolutely correct.

09-07-2007, 07:08 AM	#4
Gabriel Torres Administrator Join Date: Oct 2004 USA Posts: 2,553	Hi there, Yes, I made a huge mistake stating that AMD processors don't use HT2. I will fix this ASAP. I am studying more about this stuff. Please hold on. And thanks a lot for pointing this out to me. Cheers, Gabriel.

09-19-2007, 07:25 AM	#5
Gabriel Torres Administrator Join Date: Oct 2004 USA Posts: 2,553	Just to let you guys know that I've just updated our HyperTransport tutorial correcting some mistakes I wrote. Basically, I've said HyperTransport 2.0 was never used on AMD CPUs, which is quite wrong -- all current AMD CPUs are based on HT2 using, however, the lower speed grade provided by this version of HyperTransport. It is just that AMD does not say anything about the HyperTransport version they use on their datasheets, what got me confused.