If you have time: > A real AMD64 machine can also run with more than 4GB of ram and do DMA > without having to bounce buffering to PCI devices. We don't do > software bounce buffering yet to cope with this deficiency in > large-memory Intel AMD64-clones.
You're talking about DMA to really high memory, i.e. above physical 4GB, is that right? I'm not that clued in with hardware, and I don't know where to search to find out the answer to this, but: all I/O devices these days can do DMA to above 4GB in big 64-bit systems, but a limitation in the Intel hardware means that the kernel has to intercept this to help, by catching it in a low memory buffer and then transferring the data to higher memory manually, or by doing memory-to-memory DMA into high memory, or something. But the AMD64 hardware can do it directly without help to bounce the data from low to high, supporting DMA directly to physical RAM 4GB+? But none of this applies to devices that want to DMA below 4GB, because that has always been supported. It only applies on Intel machines with 4GB+ RAM when devices want to DMA to 4GB+ but their DMA chips or the processor itself can't do it without software help from the kernel. > (And besides that, the Intel ones being slower, and using a whole lot > more power) I'm glad, because I've ordered an Athlon64 3000+ Venice core processor (chickened out on spending $500+ on a San Diego 4000+ or X2 3700+). It would be nice if my compiles were as fast or faster than my Celeron D 336 2.8GHz and my Pentium 4 3GHz with 1MB L2 cache.
