On 2/13/2012 9:02, Warp wrote:
> does disk I/O have to share, and hence compete for, the same memory
> bus as the CPU

On modern desktop type machines, I think the disk probably steals memory 
cycles from the CPU. That's a good point. On the other hand, what's the 
transfer rate of even a fast disk? 120MBps?

> and, more significantly, the GPU, when transferring data
> from the main RAM to it)?

I wouldn't think the disk's DMA would affect CPU->GPU at all, since AGP bus 
and later, but I'm not sure. Of course, the CPU has to read from the RAM as 
well, so it's hard to say.

> data transfer performance in other critical areas (such as transferring
> data from the main RAM to the GPU, which happens all the time).

An excellent point I hadn't considered. Honestly, I haven't really thought 
about this stuff since the generations of machines where RAM is faster than 
CPUs. :-)

That said, given that a level in Portal (say) can take a couple minutes to 
go through, and a level takes maybe 15 seconds to load, keeping the transfer 
rate down to 1M/s or something might even speed things up there. Especially 
when you're talking about loading it off a DVD instead of a HD, where the 
seek times will still dominate.

-- 
Darren New, San Diego CA, USA (PST)
   People tell me I am the counter-example.

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