Benjamin Gawert

November 1st 05, 04:09 PM

Skybuck Flying wrote:

[removed the groups where this is OT]

> Q1: Some websites specifications say:

>

> 1. The Athlon X2 4800 processor is limited to 6.4 Gigabyte/sec of memory

> bandwidth.

> 2. Intel Pentium Extreme Edition processor is limited to 6.4 Gigabyte/sec of

> memory bandwidth.

>

> Case 1. Does this mean 3.2 Gigabyte/sec in both directions ?

No. The FSB of the Pentium4 is bidirectional, being able to do 6.4GB/s

in both directions. The AMD x64 CPUs (Athlon64, Opteron) use

Hypertransport links that are unidirectional...

But then, with intel all processors share the same FSB which is a really

big limitation when having more than one CPU...

> Case 2. Or is it possible to have 6.4 Gigabyte/sec going in one direction ?

Right.

> Q2: Some website specifications say (more or less):

>

> PCI-E 16x slot is 8 Gigabyte/sec, 4 Gigabyte/sec IN and 4 Gigabyte/Sec out

> PCI-E 8x slot is 4 Gigabyte/sec, 2 Gigabyte/sec IN and 2 Gigabyte/Sec out

> PCI-E 4x slot is 2 Gigabyte/sec, 1 Gigabyte/sec IN and 1 Gigabyte/Sec out

> PCI-E 2x slot is 1 Gigabyte/sec, 512 Megabyte/sec IN and 512 Megabyte/Sec

> out

> PCI-E 1x slot is 512 Megabyte/sec, 256 Megabyte/sec IN and 256 Megabyte/Sec

> out

One PCIe link (PCIe 1x) provides 250MB/s in and out. PCIe 16x can do

4GB/s in and out.

> Case 3. So does this mean that PCI-E 16x slot is limited to 4 Gigabyte/sec

> in one direction ?

No. 4GB/s in every direction. PCIe is unidirectional...

> Case 4. Or is it possible to go 8 Gigabyte/sec in one direction ?

No.

> Furthermore it seems current SLI motherboards when in SLI mode,

> turn the two PCI-E 16x slots into PCI-E 8x slots.

Right.

> So the bandwidth that is available in SLI mode is the same as in SINGLE

> mode.

Regarding the overall bandwith, yes.

> Anyway in both cases this would mean a maximum input for the graphics cards

> of:

>

> Single: 4 Gigabyte/sec Input.

.... and output.

> SLI: 2 Gigabyte/sec + 2 Gigabyte/sec = 4 Gigabyte/sec Input.

No. 2GB/s in and out. You can't just add these numbers...

> So that would leave 2.4 Gigabyte/sec for output.

> (from graphics card back to RAM)

> Single: 2.4 Gigabyte/sec Output

>

> SLI: 1.2 Gigabyte/sec + 1.2 Gigabyte/sec = 2.4 Gigabyte/sec Output.

No. 4GB/s for single gfx card and 2GB/s for SLI...

> So if I were to buy such an SLI motherboard it would be pointless to buy a

> graphics card which can handle more than 2 gigabyte/sec of input and more

> than 1.2 gigabyte/sec of output.

No. Even 2GB/s are much more than what even the latest and greatest

games need....

> Q3: How much bandwidth can the new Nvidia GTX 7800 process for input and

> generate for output ?

The 7800GTX has a native PCIe 16x interface which can handle up to 4GB/s

in and out (16x 250MB/s)...

The internal bandwith between GPU and gfx card RAM is much higher,

though. The 7800GTX has an internal bandwith of around 38GB/s (yes,

gigabytes!) between the GPU and the gfx card memory...

> Q4: How much bandwidth can the processors handle ?

see above.

> Alternatively I could wait for new motherboards to come out with FULL

> BANDWIDTH PCI-E 16x slots.

Won't take long...

> Then the picture would look like this:

>

> Single: 4 Gigabyte/sec Input.

.... and output.

> SLI: 4 Gigabyte/sec + 4 Gigabyte/sec = 8 Gigabyte/sec Input.

.... and output.

> BUT this is now limited by the the processor/memory controller: 6.4

> Gigabyte/sec

>

> SLI: 3.2 Gigabyte/sec + 3.2 Gigabyte/sec = 6.4 Gigabyte/sec Input.

>

> That would leave no room for output... that s bad.

Nope. As I said even PCIe8x is much more than current and even future

games need....

> So I think I must come to the conclusion that with this processor/memory

> controller/bandwidth limitation waiting/buying this new motherboard will

> solve absolutely nothing. Since the bottleneck is in the processor/memory

> controller.

Nope. The

> Anyway these dual core processors are very expensive.. so just upgrading

> them in the future for a little bit more bandwidth seems crazy.

>

> My conclusion is as follows:

>

> 1. If the single card (the gtx 7800) is able to handle 6.4 Gigabyte/sec of

> input + output then I don't need SLI ;)

Apples and oranges. SLI is not there to improve bus performance. SLI is

there to improve rendering speed. Again, the busses are more than fast

enough. The limitation still is the GPU, that's why there are techniques

like SLI...

Benjamin

[removed the groups where this is OT]

> Q1: Some websites specifications say:

>

> 1. The Athlon X2 4800 processor is limited to 6.4 Gigabyte/sec of memory

> bandwidth.

> 2. Intel Pentium Extreme Edition processor is limited to 6.4 Gigabyte/sec of

> memory bandwidth.

>

> Case 1. Does this mean 3.2 Gigabyte/sec in both directions ?

No. The FSB of the Pentium4 is bidirectional, being able to do 6.4GB/s

in both directions. The AMD x64 CPUs (Athlon64, Opteron) use

Hypertransport links that are unidirectional...

But then, with intel all processors share the same FSB which is a really

big limitation when having more than one CPU...

> Case 2. Or is it possible to have 6.4 Gigabyte/sec going in one direction ?

Right.

> Q2: Some website specifications say (more or less):

>

> PCI-E 16x slot is 8 Gigabyte/sec, 4 Gigabyte/sec IN and 4 Gigabyte/Sec out

> PCI-E 8x slot is 4 Gigabyte/sec, 2 Gigabyte/sec IN and 2 Gigabyte/Sec out

> PCI-E 4x slot is 2 Gigabyte/sec, 1 Gigabyte/sec IN and 1 Gigabyte/Sec out

> PCI-E 2x slot is 1 Gigabyte/sec, 512 Megabyte/sec IN and 512 Megabyte/Sec

> out

> PCI-E 1x slot is 512 Megabyte/sec, 256 Megabyte/sec IN and 256 Megabyte/Sec

> out

One PCIe link (PCIe 1x) provides 250MB/s in and out. PCIe 16x can do

4GB/s in and out.

> Case 3. So does this mean that PCI-E 16x slot is limited to 4 Gigabyte/sec

> in one direction ?

No. 4GB/s in every direction. PCIe is unidirectional...

> Case 4. Or is it possible to go 8 Gigabyte/sec in one direction ?

No.

> Furthermore it seems current SLI motherboards when in SLI mode,

> turn the two PCI-E 16x slots into PCI-E 8x slots.

Right.

> So the bandwidth that is available in SLI mode is the same as in SINGLE

> mode.

Regarding the overall bandwith, yes.

> Anyway in both cases this would mean a maximum input for the graphics cards

> of:

>

> Single: 4 Gigabyte/sec Input.

.... and output.

> SLI: 2 Gigabyte/sec + 2 Gigabyte/sec = 4 Gigabyte/sec Input.

No. 2GB/s in and out. You can't just add these numbers...

> So that would leave 2.4 Gigabyte/sec for output.

> (from graphics card back to RAM)

> Single: 2.4 Gigabyte/sec Output

>

> SLI: 1.2 Gigabyte/sec + 1.2 Gigabyte/sec = 2.4 Gigabyte/sec Output.

No. 4GB/s for single gfx card and 2GB/s for SLI...

> So if I were to buy such an SLI motherboard it would be pointless to buy a

> graphics card which can handle more than 2 gigabyte/sec of input and more

> than 1.2 gigabyte/sec of output.

No. Even 2GB/s are much more than what even the latest and greatest

games need....

> Q3: How much bandwidth can the new Nvidia GTX 7800 process for input and

> generate for output ?

The 7800GTX has a native PCIe 16x interface which can handle up to 4GB/s

in and out (16x 250MB/s)...

The internal bandwith between GPU and gfx card RAM is much higher,

though. The 7800GTX has an internal bandwith of around 38GB/s (yes,

gigabytes!) between the GPU and the gfx card memory...

> Q4: How much bandwidth can the processors handle ?

see above.

> Alternatively I could wait for new motherboards to come out with FULL

> BANDWIDTH PCI-E 16x slots.

Won't take long...

> Then the picture would look like this:

>

> Single: 4 Gigabyte/sec Input.

.... and output.

> SLI: 4 Gigabyte/sec + 4 Gigabyte/sec = 8 Gigabyte/sec Input.

.... and output.

> BUT this is now limited by the the processor/memory controller: 6.4

> Gigabyte/sec

>

> SLI: 3.2 Gigabyte/sec + 3.2 Gigabyte/sec = 6.4 Gigabyte/sec Input.

>

> That would leave no room for output... that s bad.

Nope. As I said even PCIe8x is much more than current and even future

games need....

> So I think I must come to the conclusion that with this processor/memory

> controller/bandwidth limitation waiting/buying this new motherboard will

> solve absolutely nothing. Since the bottleneck is in the processor/memory

> controller.

Nope. The

> Anyway these dual core processors are very expensive.. so just upgrading

> them in the future for a little bit more bandwidth seems crazy.

>

> My conclusion is as follows:

>

> 1. If the single card (the gtx 7800) is able to handle 6.4 Gigabyte/sec of

> input + output then I don't need SLI ;)

Apples and oranges. SLI is not there to improve bus performance. SLI is

there to improve rendering speed. Again, the busses are more than fast

enough. The limitation still is the GPU, that's why there are techniques

like SLI...

Benjamin