NVIDIA?s nForce2 with dual channel features would be able to feed AGP8X (~2GB/s), since EV6?s ~3.2GB/s consumption can only use a single MC channel from a dual channel MC pool. This is ideal for bloated games (e.g. DOOM3@max texture details) that exceed the mainstream GPU's 128MB/256MB memory capacity.
A typical value-end 333FSB K7 Athlons XP/K7 Sempr0n/nForce2 based systems can feed AGP8X (2GB/s) without any difficulties.
You're assuming that the North Bridge only has a single 64-bit 133MHz memory channel equipped with PC2100. I don't know of any AGP 8x capable chipset that has a memory sub-system that feeble. Most currently available chipsets have significantly better specifications.
I'll take the NForce 2 Ultra 400 as an example, because it's cheap and very popular. It has a pair of independent memory controllers each with their own 200MHz 64-bit channel for use with PC3200 memory, giving 6.4GB/sec of theoretical throughput. The processor's FSB maxes out at 3.2GB/sec so there's always enough bandwidth available to satisfy the demands of the AGP bus (even factoring in real-world dram effeciency), and the seperate controllers mean it's possible for AGP-Memory transfers to be completed without interruption even when the CPU is performing heavy memory I/O.
The NF2 North Bridge also permits CPU-AGP transfers to take place concurrently with memory operations, because the DASP unit can pre-fetch data from memory into its 64Kb buffer while denied access to the CPU because of CPU-AGP activity.
Other modern systems like the Intel 845, 915 and 925 chipsets work similarly except that they implement a single 128-bit memory controller, rather than the NForce's dual 64-bit units.
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