How is programming for the Cell Processor on the PS3 different than programming for any other processor found on a normal desktop?
What kind of programming paradigms, techniques, and practices are used to fully utilize the Cell Processors potential?
All the articles I hear concerning PS3 development discuss, "Learning how to program on the Cell Processor." What does this really mean beyond some hand waving?
In addition to everything George mentions, the SPUs are really better thought of as streaming vector processors. They work best when you have an algorithm that works on long sequences of numerical data, which can be fed through the SPU's limited memory via DMA, rather than having the SPU load a chunk of memory, try to operate on it, find that it needs to follow a pointer to somewhere outside its memory, load that, keep going, find another one, and so on.
So, programming for them isn't a simple model of concurrency and threads; it's more like high performance numerical or scientific computation. It is also non-uniform memory access taken to an extreme.
Furthermore, every processor is in-order with deep pipelines, so the programmer has to be much more aware of data hazards and instruction bubbles and all the numerous micro-optimizations that we are told the compiler "should" take care of for us (but it really doesn't). Things like mispredicted branches, load-hit-stores, cache misses, etc. hurt a lot more than they would on an out-of-order processor that could juggle the order of operations around to hide such latencies.
For concrete examples, check out Mike Acton's CellPerformance blog. Mike is my favorite old-school assembly-happy perf curmudgeon in the business, and he's really earned his chops on this issue.