NVIDIA GeForce 256 Part 1: To buy or not to buy

The GeForce 256 is completely AGP 2X and 4X compatible but it boasts a technology that is designed to improve performance when operating in AGP 4X mode on AGP 4X compliant motherboards (i.e. i820): Fast Writes.

Fast Writes is essentially a method of allowing the CPU to send data directly to the AGP bus without having to use main system memory as described by the illustrations below. The data is based on the assumption of a CPU polygon throughput rate of 2 million triangles per second and 90 byte triangles resulting in a 180MB/s data transfer. It is also based on the assumption that upcoming games will require 5X the triangle performance, increasing the memory bandwidth requirement to 900MB/s. Let's take a look at NVIDIA's explanation for the need and in Part 2, we'll be taking a look at our benchmarks of Fast Writes and whether or not the feature is really anything other than PR hype.

Here we have a standard 100MHz BX system transferring 180MB/s of data.  There are no real bottlenecks made obvious by this diagram.

Here we have NVIDIA's estimate as to what bandwidth requirements for "next generation" gaming applications.  Notice that the calculations are based around an i820 system running at the 133MHz FSB.

And here we have the same AGP 4X i820 system from above but using "Fast Writes" on the GeForce 256.   This cuts the issue of system memory bandwidth out of the equation but how much of a real world performance increase does it offer?  We'll save that for part 2..