How do logic gates calculate their output?

Question

Do transistors calculate the output? If so, wouldn’t transistors be the most fundamental logic of computers?

Thanks.

In: Technology

Answer 1

To understand computers you have to understand that everything is built upon layers and layers (and layers and layers) of abstraction. Just like a computer language like C is an abstraction of a more low level form like Assembly (which is itself an abstraction of the pure binary), logic gates are an abstraction of groups of transistors that together do a simple operation.

So, if I’m going to design a circuit that adds two numbers together, yes I could go down to the very lowest level and map out every circuit and transistor involved, but doing so would be complicated and difficult to troubleshoot. Sticking an abstraction layer of logic gates in there makes it a much more human tractable problem.

In reality a ton of chip design is done by computers these days with even higher level abstractions on top for human readability and input. Verilog for instance more closely resembles computer code than what you might expect chip design to look like.

But none of that is a very good ELI5, so let me try again.

Logic gates are like Lego blocks, the simple old fashioned ones. You **could** build the exact same models out of only flat Lego pieces and not using blocks at all, just stick the flat plates together until you get the shape of the larger blocks. But no one would want to do that, it would be tedious and you’d likely mess it up somewhere along the line. If you really had to build a whole set out of only flat pieces, you’d probably start by putting flat pieces together into the shape of the larger more friendly blocks that the instructions actually call for.

Transistors are the flat pieces, by themselves it doesn’t look possible to make much interesting out of them. But when you think about a collection of flat pieces as a bigger block it’s easier to imagine making a huge castle from them.

So what’s more fundamental, the shapes that people build with every day or the shapes that deep down make up those shapes? It’s just a matter of semantics.