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Formula for Memory Bandwidth?

Forum Motherboards & Memory : Memory - Formula for Memory Bandwidth?

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tuesday630   02-17-2003 at 10:56:09 PM

Does anyone know how to calculate a north bridge's memory bandwidth? For example, Intel says that its E7205 has 4.2GB/ps of memory bandwidth. VIA claims the KT400 can do 2.7GB/ps and 3.2GB/ps for its P4X400. nVidia says that the nForce2 can do 6.4GB/ps (due to its dual 64-bit controllers).

Anyone know the formula? Thanks.

---There may be more than one way to do it, but why would anyone want to remove the fur from a feline?---

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juin   02-17-2003 at 11:22:16 PM
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MGHZ X bit path X nb of transaction X size of the packet.

RDRAM PC 1066

133*16*4*2=166.3 Gbit divide per 8 for having bytes for 2.08 GB/S per module

Pc3200
200*64*1*2=3.11 GB/S

Stupid question 1 GB is 1028 or 1024 MB

Just next to the lab and the bunker you will find the marketing departement.

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tuesday630   02-18-2003 at 12:22:08 AM
- 0 +

Okay, I get some but not all.

By "MGHZ" I'm assuming you mean the Base memory speed of the DIMM, as PC3200's is 200MHz.

By "Bit Path", I think I understand it as the Bus Width in Bits, which would be 64.

I don't know what you mean by "nb of transaction."

By "Size of the packet", I think I understand that DDR is 2 bytes wide.

Please help me with "nb of transaction" and I'll study it further. Thanks.

---There may be more than one way to do it, but why would anyone want to remove the fur from a feline?---

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tuesday630   02-18-2003 at 02:36:51 AM
- 0 +

Hey, I'm noticing that if I multiply the FSB rating by 8, I'm coming up with the memory bandwidth ratings that the chipset makers are publising. So, FSB of 533MHz * 8 = 4.2GBps and 400 MHz * 8 = 3.2GBps. Dual-channel works like this multiplied by 16.

Unfortunately, it's not consistent, but when it's not, the published numbers see to be the highest speed rating of the RAM multipled by 8. This seems especially true for AMD chipsets and 333MHz FSB.


---There may be more than one way to do it, but why would anyone want to remove the fur from a feline?---

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