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I wonder how the designers "knew" or hoped that the S/360 instruction set was achievable with that hardware/microcode design. Was it sufficient to cover all th

I wonder how the designers "knew" or hoped that the S/360 instruction set was achievable with that hardware/microcode design. Was it sufficient to cover all the instructions? The floating point portion seems like a likely risk. (Perhaps, more likely, the microcode drafts were co-written with hardware designs so they had less risk of a failure.)

kens 5y ago
There's not really much risk. Because the S/360 was built from gates (SLT) rather than an integrated circuit, they could easily change the design if needed. (Even at a customer site!) It's not like a microprocessor chip that would require an expensive re-spin if something went wrong. So if they discovered they needed another micro-operation, they could just add it to the design. There are a few micro-operations that seem rather contrived, as if they realized it would really help performance to do this random combination of things.