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Simplest explanation, that universal logic chips MUST have very wide tolerances, to be really universal. - They have to use significantly higher voltages and consider higher currents, than really need to work. For example, typical logic output of universal TTL logic, considers connect to it more than 10 inputs, each of them drain some current. And also, universal logic i/o MUST tolerate some differences in power supply voltages and interference on real circuits. But if you don't need to communicate to outside of chip, you could make things much more optimized, make customized outputs, considering for only as much drain as really exists in scheme; make internal highly stabilized power supply and very powerful power distribution network. For first CPUs this was not talked, they just considered as very expensive logic chip, but ~ from 80186, hard to say exactly date, appears division: some outputs become high power, others stay "normal", low power. And in commodity cpus, in Pentium appear two voltages - one for core and other for interface circuits. |