How to understand computer architecture?

Question

Iron

Please tell me how to understand this information:

I read that in the 40s there were only 2 levels of architecture in digital computers: ISA and digital logic level. At the ISA level, programming was carried out, and at the digital logic level, programs were executed.
Then in 1951, there was an idea for a 3-level computer, in which a microarchitecture level was added between the ISA and the CLU, on which the interpreter (microprogram) was located. It would follow that the ISA level commands would be interpreted at the microarchitecture level, which would cause the hardware to execute microprograms with a limited instruction set, which would increase system reliability by reducing the number of lamps.

Explain how the addition of the layer made it so that the hardware now executes microprograms with a limited set of instructions, while not before. It turns out before the ISA level did not consist of a limited set of commands? Why add another intermediate level. At the lowest level, the same code is still executed. Can you give some human-readable example to understand this topic.

Answer 1

Read about Microcode on Wikipedia, also this article https://habr.com/post/427757/ . There are answers to your questions.

Answer 2

Can you give a human-readable example?

Gearbox, for example, a car. At first, there was nothing, and the speed or power was regulated directly by pressure and the amount of steam. Then a mechanical box appeared - the movement of the lever moved the gears on the shafts, different gear ratios gave different forces and speeds. After that, automatic boxes, CVTs, robots appeared. But at the lowest level, everything works according to the original principle.