Harr: Let's assume that there's at least one or more instruction-set processors on the chip. What needs to be defined next is whether there are multiple instruction-set processors on a chip, or one instruction-set processor and many custom data path processors with possibly variable control. Gupta: With instruction-set processors, it's not just a question of what that underlying component does, but also at what level the software is integrated? Are we integrating at the compiler level or at the lowest level? In that sense, " system on chip " is pretty broad. " Systems on chip with reprogrammable DSP processors " is also very broad— " system-on-chip multiprocessors " is a much narrower term to use. Olukotun: The classic multiprocessor chip has several instruction-set processors. We have everything from symmetric multiprocessors that share a central memory, to ones with a network between the processors, which are communicating via message passing. Putting all these architectures on a single chip is what people classically mean when they talk about multi-processor chips. The processors may not necessarily all be the same; they could be specialized. Jerraya: The multiprocessor concept, in which " multiprocessor " means having several master processors on a chip, is central to our discussion. These processors can be programmable instruction sets or they can be specific hardware. But the key concept is that you have several masters, each with its own bus. The main issue is how to connect these through a processor network. Harr: We can now put more than just the instruction-set processor on a chip. With floating-point operations, we still have 90% of the chip left over. With all this extra real estate available, we could look at multiple instruction-set processors or heterogeneous instruction-set processors with custom data paths intermixed—all sharing buses, memory hierarchies, and so forth. Vissers: The application domain is shifting from desktop computers and multiprocessors One of the advances that will be enabled by system-on-chip (SOC) technology is the single-chip multiproces-sor. As VLSI technology improves to allow us to fabricate hundreds of millions of transistors on a single chip, it will become possible to put a complete multiprocessor, including both CPUs and memory, on a single chip. Single-chip multiprocessors will be useful not just in low-cost servers but also to perform video and a wide variety of consumer applications. The advent of single-chip mul-tiprocessors will require us to rethink multiprocessor archi-tectures to fit the …