system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: CPU / GPU manufacturing processes.

So I have a 45 nanometer CPU in my computer. What exactly is 45nm wide? Are there wires in there? Is it etched into whatever that disc is?

The only thing I've ever seen on how they're made is a big shiny disc that gets some sort of liquid squirted on it, then the disc spins.
gpt
There can be wires inside your chip, but only going from the pins to the silicon. The silicon itself (the actual physical semiconductor material which is housed within the body of the processor) doesn't use *wires* per se, but there are straight tracks etched into it at the nanoscopic level for carrying signals and current to various parts of the chip. We call the actual silicon bit inside the CPU housing the "die".

That disc you're referring to is called a "wafer". It's actually anything from a few dozen to a few thousand CPU dies (depending on their size and how many will squeeze in). The dies spend most of their life in the factory stuck together in a circular wafer, which is why you most commonly see them like that.

The creation of a CPU can involve well over a hundred different processes, including 'etching' and the liquid bath you described.

It helps to know how silicon works as a semiconductor. It's called a semiconductor because in reality, pure silicon is actually pretty crap at conducting electricity. But, when combined with *impurities* in a controlled fashion, select parts of the silicon can be made to be conductive. We call this process "doping".

Doping with different impurities produces different effects and can be combined in different ways to get different results, which can be used to build nanoscopic components on the silicon which all function in a specific way, such as transistors, which can be thought of as little electrically-operated switches, capacitors, which are used to store data (charged for 1, empty for 0), diodes, which only let electricity flow in one direction through them, and so on.

To do this, a lithographic process is used whereby the wafers are exposed to very finely detailed patterns of light, shone through a "template" of various layers of the CPU design in question. Imagine how shadow puppets work with your hands and a torch - it's that, but with a circuit design instead, and at a nanoscopic level. The light reacts with and hardens a photoresist material which is applied on top each time so that when they are exposed to, say, a light hydrofluoric acid bath, some nanoscopic portions (which were not exposed to light) are etched away and some remain because the photoresist protects them. The next layer of dopant can then go on top, and then some photoresist, and a new template, and the process repeats to effectively dig/layer a design into the chip.

As for how they make various different designs of chip - different models with different speeds, numbers of cores, cache etc, the secret is that they actually don't. This is because mastering a new design is enormously expensive and time consuming. Instead, they just re-use the same design for different models. 

Take for example AMD's tri-core CPUs. These were actually quad cores, but in testing, one core was found to be defective, so it was shut down and repackaged as a "tri core" CPU. Sometimes, other defects occur, like the chip won't run at the desired frequency, so it's set to a lower one and packaged as a lower model instead. Other times, some of the cache is damaged, so they disable it and sell it as a lower model with less cache.

Sometimes, nothing is wrong with the chip at all, but they disable parts of it anyway so they can meet demand for their lower-end processors.

Why do they do this? To increase "yield", which is the semiconductor industry's biggest pain the arse. If you can repackage a processor as a lower model instead of throwing it away, you recoup more costs for each wafer you make because more of the dies etched on it are viable products which bring in money. In turn, the consumer saves a ton of money because the manufacturer doesn't have to charge them an arm and a leg to cover the costs of all the chips that would be otherwise thrown out.

Funnily enough, the process of repackaging chips to avoid throwing them out is called "binning". It happens with most makes and models of CPU and GPU, pretty much.