Quad Pumped Bus?????????

[FastD]

The p4 seems to have lots of memory bandwidth and everyone keeps talking about the p4's quad pumped bus.. but.. but..From what I could see it is simply a dual channel rambus design. 2X1,6gb/sec equals 3,2gb/sec right?

So what about it is it that makes it quad???.. They don't call the 840 chipset quad pumped and it has the same bandwidth as the 850.. In theory anyway.

btw.. why does the 850 sport so much higher real life memory bandwidth than the 840?


Ok.. one more thing. What are the high latencies of RDRAM that everyone keeps talking about?

/patrik

 

[soulm4tter]

you are confusing 2 different things. quad pumped is in reference to the actually FSB of the chipset. that is the speed at which the chipset talks to the cpu and memory. The bus is actually 100mhz, but its 4 times per 1 bus cycle. Memory bandwidth is the speed at which the memory can supply data to the cpu.

 

[FastD]

Oh ic.. Thanx for sheding light on this!

/patrik

 

[Goi]

soulm4tter's right, but frankly, I don't really understand how the quad pumping works. DDR works by accessing data on both clock edges per clock cycle, and 1 clock cycle obviously only has 2 edges, so where does that extra 2X come from?

 

[Soccerman]

I'll go into a bit more detail..

the CPU is but one device that is connected to the Northbridge chipset. that chip is the center in a star topology consisting of RAM, AGP port, the SouthBridge, and the CPU.

in other words, each of those devices are connected to the northbridge with their own data link.

the CPU on the P4/i850 setup connects using a bus which is quad pumped. (no I don't know how exactly they do that). it's width is 64 bits, and it operates at 100mhz. it's bandwidth is 3.2 gigs/second

the RAM is more complicated. there are really two connections to the northbridge when it comes to the RAM. both channels are 16 bits wide, and operate at 400mhz, and are DOUBLE pumped. their overall throughput is 3.2 gigs/second.

the AGP bus is capable of running at AGP 4x. that's 66mhz, 64 bits wide, and quad pumped. overall bandwidth is 2.2 gigs/second.

now, I don't remember how the i850 chipset connects to the southbridge..

finally, the terminology that they use is also totally different. I actually think that I made a mistake on this.

 

[Goi]

I know all that Soccerman, I was just asking about the details of how quad pumping actually works.

 

[Soccerman]

Goi, that was for the person who was asking..

 

[Goi]

Oh ok Soccerman, didn't realize that, sorry...
Now can someone answer mine?