NV44's memory subsystem, especially the memory controller and new peripheral memory management unit (MMU) is a new departure for NVIDIA. Under the TurboCache marketing umbrella, the memory subsystem uses PCI Express to allow read and write of local system memory by the GPU. It's not quite AGP, since AGP could never texture back into memory, only read from AGP locked memory to the GPU or dump the entire framebuffer back on the host, whereas using PCI Express, NV44 can use local memory as a fully read/write data store for a number of data objects it routinely works with.
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