| sieanr said: The RSX suffers from latency when reading or writing to the XDRAM. Latency and a bandwidth bottleneck are two different things. |
I think this has been extensively covered already.
- The Xenon CPU has to get all its RAM through the GPU, using a shared bus to access the slower GDDR3 memory.
- The Cell is connected directly to the much faster XDR RAM.
- The Xenos GPU has to share the bus to the GDDR3 memory with the CPU, limiting available bandwidth.
- The RSX is directly connected to the GDDR3 memory, but is allowed to access the faster XDR ram through the Cell's EIB as well. I guess the later option will not be used much, 256 MB should in normal situations be sufficient. Also the default harddrive could function as a provider of virtual memory, if somehow 512 MB of system RAM wouldn´t be enough (a PS3 advantage, because of the default harddrive), but I guess if using the Blu-Ray drive to stream data (so smaller parts of game data needs to be loaded into memory) the harddrive could rather serve for caching.
To quote my earlier post:
'For most stuff, the memory directly connected to the RSX will be used, but there is enough bandwidth to use the XDR memory as well. I've heard of developers using the XDR as additional texture memory as it not only increases texture memory it also increases texture bandwidth. The latency will increase but RSX this isn't a big problem for GPUs and RSX has bigger than usual caches anyway.
I've also heard of developers writing compressed textures directly from the SPEs to the RSX, this bypasses memory altogether so so effectively reduces latency while increasing bandwidth.'
Reading back some posts I guess, the RAM confusion you complained about was already covered.
Essay Pro
