im not enitirely sure how cpu's break down instructions. it probably takes a simple instruction and breaks it down into simpler operations. you concept of digital logic is not right. an ISA is just a bunch of instructions a processor executes. the processor doesnt need special logic for that particular isa. it just needs to be able to execute every instruction.
here is a simple decoder. its like a switch in a network. its not some complex decrypting magic.
http://www.asic-world.com/digital/co...er_using_Demux
i understand what you are saying: could an x86 decoder allow instructions to run on a gpu? no. there are many issues. gpu's are still asic's. they are designed around directx. they dont support all of the features that would be needed in a cpu and they are very different architecturally. for instance sse has 8 GPR's(general purpose registers). evergreen has 128GPR's. both are 128 bits wide. an sse programmer cant use 128 gpr's because 120 of them dont exist!






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