by Bubba "Masterfung" Wolford

  PC800 RDRAM

I have mentioned earlier that SDRAM just did not have the bandwidth and speed to get Intel where it needed to go. So we can understand "why" this is the case, let's go over some calculations. This is the transfer rate of a DIMM of PC100 RAM:

(64-bit memory x the memory bus speed (100 MHz)) / by 8 bits per byte = 800Mb/sec.

This looks like a pretty good amount of data, doesn't it? Well let's see how much data your CPU can transfer around. This calculation is totally irrespective of the actual speed of your CPU:

(64-bit bus x the 100 MHz bus speed) / by 8 bits per byte = 800Mb/sec.

So now you can understand that the CPU and PC100 RAM are right in tune with each other in actual throughput for your computer! Now let's throw another calculation into the works. How does your current AGP 2X system fit into this equation?

(32-bit bus x by the 66 MHz AGP bus x the 2X transfer rate) / by 8 bits per byte = 528Mb/sec.

So, the AGP bus is not even capable of saturating the CPU or memory bus. This works great right now! I think you guys can see it coming though. When we double the AGP bus, we are going to see a huge bottleneck in the works! Here is the calculation for AGP 4X:

(32-bit bus X 66 MHz AGP bus X the 2X transfer rate) / by 8 bits per byte = 1.06GB/s

Uh oh! We have a serious bottleneck now! Now we are losing over 200Mb/sec. in data transfer rate due to a bottleneck in the CPU and memory bus. What happens if we increase the system bus speed to 133 MHz:

(64-bit bus X 133 MHz bus speed) / 8 bits per byte = 1.06Gb/sec.

We have achieved parity again! Now the system bus is the same as the AGP 4X bus transfer rate. We still have one problem though! Our memory is now the bottleneck, only being able to transfer data at 800Mb/sec. Look what happens when we switch to our PC800 RAM:

(16-bit bus X 400MHz speed of the RDRAM X 2X transfer rate) / 8 bits per byte = 1.6Gb/sec.

Alright! Now we are talking! We have some good 60% growth rate here with RAMBUS PC800 RAM. Even if the bus speed is increased to 200 MHz we will still be able to allow the PC800 RAM, CPU and system bus to run at full speed with no slowdowns. If the AGP frequency is increased to 6X we will still be able to run all three of these critical components at full speed with no slowdowns.

We can see here that PC800 RAM can run on either a 100 MHz bus, a 133 MHz bus or even a 200 MHz bus. The down side of using RDRAM is that is it expensive right now. However, all memory is expensive right now. Once Intel actually ships the i820 and RAM manufacturers begin to shift production away from PC66 and PC100 and toward RDRAM, we will start to see prices on RDRAM tumble.

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RIMMs

Another downside to RDRAM is that the latency of RDRAM is slower than that of PC100. However, to think that slower latency is really a drawback to RDRAM after weighing the two in terms of advantages/disadvantages, the thought of knocking RDRAM due to slower latency becomes very feeble.

PC700 RDRAM

Now that we have gone through the majority of the calculations to demonstrate why RDRAM is necessary for proper data transfer, I can tell you that running PC700 RAM will be almost as good a solution as PC800 RAM. Lets look at the calculation of PC700 RAM:

(16-bit bus X 350 MHz speed X 2X data transfer rate) / 8 bits per bye = 1.4Gb/sec.

Well, there is some slowdown here but still more than enough to handle the increased bus speed and AGP 4X. PC700 RAM can run on either a 100 MHz bus or a 133 MHz bus. However, running PC700 RAM on a 200 MHz bus will not be possible.

PC600 RDRAM

This is the slowest kind of RDRAM that will run on the new Camino i820 motherboard. It does not support the 133 MHz bus speed. Even though it has a throughput 1.2BGb/sec., it will only be supported on the 100 MHz bus. Why this is the case, I do not know. It is still plenty fast but for the sake of future upgrading, I would recommend that anyone buying RDRAM for an i820 motherboard, skip PC600 and go straight to PC700 or even better, PC800 RDRAM.

133 MHz FSB

No doubt that any extra increase in the speed of the bus is going to help the computer. In this case, you can see why the increase to 133MHz was the minimum necessary to keep the system board from becoming a bottleneck in the computer. I would expect Intel's next bus speed increase to be either 166 MHz or more likely, 200 MHz.

AMR (Audio / Modem Riser)

This is a new implementation that Intel has married to the i820. Essentially the AMR is a pre-built hardware implementation for an audio device and a modem. The user simply buys the external "Codec", which will be much cheaper for everyone including the consumer, plugs it in, and you have great sound and 56K modem speed. The only downside of using this AMR is that it will steal valued CPU cycles to perform its software and hardware calls.

New Hub Architecture

Removal of the ISA slot altogether and removal of the slower PCI I/O in the bus. By using a newer architecture Intel has now doubled the bus speed to 266Mb/sec. This is a change from the i440BX where the North/South Bridge handled these bus communications.

Go to Part IV.