The memory bus we are all used to operates at 100MHz and is 64-bits wide. Rambus' offering runs at 400MHz (transferring on the rising and falling edges of the clock) and is 16-bits wide. What this essentially translates into is a faster Rambus interface (in terms of frequency) with added latency because of the smaller "width" of the bus.

Something that buyers will want to pay attention to is the type of memory to buy. With three flavors of Rambus memory available (PC600, PC700, and PC800), it is important to choose the speed that corresponds to the Front Side Bus you'll be running. Here is a list taken from our VC820 review:

PCxxx Memory Bus Speed: Processor Host Bus 100 MHz: Processor Host Bus 133 MHz:

PC600 300 MHz Supported Not Supported

PC700 356 MHz Not Supported Supported

PC800 400 MHz Supported Supported

Unfortunately, with only two RIMM slots onboard the P3C-E, the memory limit is 512MB. While we don't expect anyone to hit this limit in the near future, it is still a cap that isn't present on the 440BX chipset.

The final subject that is inevitably brought up is the price of RDRAM (which we feel will keep many potential buyers away from the i820 chipset). With the cost of 128MB PC800 RDRAM hovering around $1000, it may be difficult for buyers to fit into their budget.

Another feature of the board is AGP 4x, which doubles the bandwidth of the AGP bus from 528MB/s to 1.06GB/s. This is also a misleading number because, although a doubling of the memory bandwidth sounds like a drastic difference, our own tests have shown otherwise.

As more AGP 4x based video cards become available (as opposed to merely AGP 4x compliant), it will be interesting to see if this extra bandwidth ever really makes a difference. As it stands, the GeForce, TNT2 and the Viper II are the only accelerators that run at the new standard and even then the TNT2 doesn't support fast writes, the GeForce isn't yet running with sidebanding and the Viper II doesn't ship with either feature running.

Oh well, maybe some day.