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Topic Title: HyperTransport speed
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Created On: 03/08/2005 11:29 PM
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 03/08/2005 11:29 PM
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jjahir
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Posts: 13
Joined: 12/20/2004

Hello,

What is the hyper transport bandwidth for Opteron 850 4 processor system which runs at 2.4GHZ ?
Does it same as 800 series [2GHZ clock]which mention it as 1600MT/s.


What is the Memory read bandwidth to access local memory for opteron 850 processor ?

What is purpose of having 4 hypertranport channels in each processor ?.

Whether hypertransport frequency ( 800MHZ ) generated by internal clock divider ?

regards
JahirHussain
 03/09/2005 10:29 PM
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OrangesAway
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Posts: 202
Joined: 03/09/2004

QUOTE (jjahir @ Mar 8 2005, 08:29 PM) What is the hyper transport bandwidth for Opteron 850 4 processor system which runs at 2.4GHZ ?
  Does it same as 800 series [2GHZ clock]which mention it as 1600MT/s.
  What is the Memory read bandwidth to access local memory for opteron 850 processor ?
  What is purpose of having 4 hypertranport channels in each processor ?.
  Whether hypertransport frequency ( 800MHZ ) generated by internal clock divider ?

The HyperTransport bandwidth depends on multiple factors: (a) Processor (b ) Chipset (c ) Bios and other factors.

For (a), whether the Processor supports 800 Mhz or 1000 Mhz HT speed, you need to see AMD Opteron Processor Quick Reference Guide' ">http://www.amd.com/qrgserver1. It will depend mostly on the "Stepping" (or revision). The bandwidth is:

HT Mhz * 2 transfers/herz * n bits * 1 byte/8bits
800 Mhz * 2 transfer/herz * 16 bits * 1 byte/8 bits = 3.2 GB/s per direction
1000 Mhz * 2 transfer/herz * 16 bits * 1 byte/8 bits = 4.0 GB/s per direction

Just because a processor revision supports 1000 Mhz, doesn't mean it will run at that speed. The other chipsets and the BIOS have to support it.

All AMD Opterons after with CG or later support the 400 Mhz DDR DIMMS, with certain restrictions as noted elsewhere here in the forums. That would be 6.4 GB/s per processor.

At the moment, no AMD chips have 4 HT links, the most is 3. The reason why they have 3, can be explained in the AMD 4P Server Block Diagram Comparison' ">http://www.amd.com/us-en/asset...42B_One-page_FINAL.pdf , or see my reply about memory latency in the General Tech forum.

EDIT: Yes, the HT frequency is derived from an internal clock multiplier (not divider). See the BIOS guide.
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