[mjgerm]

Roughly, the power of a digital system is sum of the static power and the dynamic power (P=1/2 CV^2*F).

1. Discrete logic chips tend to be built in substantially larger process nodes (microns vs nanometers) that are less efficient. This means higher leakage current and more static power.

2. Discrete logic has to drive traces on a PCB, which have substantially higher capacitance (C) and therefore use more power getting across a board.

3. Discrete logic operates at higher voltages. Contrast 5V TTL vs. 1V core voltage inside a processor. Power is proportional to the voltage squared.

4. A microprocessor running even at low speed can replace a massive number of discrete logic chips, so for simple solutions F is low. If you're doing something very simple and interrupt-driven, F can be in the tens-hundreds of kHz.

Consequently, there's a whole lot more of both static and dynamic power with discrete logic than with a uC.

[ncmncm]

False. CMOS gates (4000-series) consume no power except when they switch. And they work at low voltage.

There are ways to make a microcontroller use less power, by making it hard-sleep when nothing is happening, but you don't get that without extra work.

[Tostino]

Appreciate that description. Helps crystalize exactly how revolutionary microprocessors were compared to other contemporary approaches.