I understand the concept of transistors and electricity flipping them to an on/off state. What I do not understand is how these transistors work. Do they physically move? How is it decided where the electricity goes? I do not understand how the power is controlled, and how it is decided what transistors activate and when
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A transistor is a special kind of semiconductor with three connections to other parts of a circuit, an input, a middle bit called the base, and an output. Formally they are called the collector, base, and emitter.
If you have a voltage applied to the input, nothing happens to your output unless you also apply a small voltage to the base. Once you do that, the full voltage from your input can flow through to the output.
So if you control the voltage going through the base, you can control the voltage going through the entire rest of the circuit. No moving parts, (other than the electricity) it’s all solid electronics.
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Processors work by taking instructions from a computer program and executing them. These instructions are broken down into simpler steps by the processor and then each step is carried out in order. The processor is like the brain of the computer and it helps to quickly perform calculations and make decisions.
The very very simple version is that through several layers of abstraction, the decision of what transistors activate when is decided by your input devices and by your software.
The less simple version is that we use an abstraction called *opcodes* to dictate what a processor does – the way this typically works is that you take a string of 8, 16, 32, or 64 bits and look at specific subsets of values in those bits to mean certain things.
As a completely arbitrary example that probably doesn’t map to any real world process, we might decide that our processor will take 8 bit inputs, and that we will split them up into a pair and two triplets, as such:
00 000 000
And so we might decide that the first pair dictates what mode we are in:
* 00 = immediate mode – send the other 6 bits directly into memory address 0
* 01 = addition mode – add the data value in the memory address specified in the first triplet to the data value in the memory address in the second triplet, and store the value in a predetermined memory address.
* 10 = logic mode – run the data from the memory register in the second triplet through binary logic gates determined by the first triplet
* 11 = unused, for future operations.
This is, again, highly simplified, in real life we would have an entire 8 bits or more dedicated to your opcode, and memory addresses that were 64 bits long. That is a very very simple processor that can do addition and data storage and not much else at the moment.
But for all other operations it is the same – that abstraction is how we describe what wires are being turned on to activate what transistors in what order.
Is everyone using chatgpt or something? The answers here are completely ignoring your focus on the actual physical workings of these things!
To actually answer the question, the principle is to do with electromagnetism. Most chips use “field effect transistors” (FETs).
Nothing actually moves, rather the electrons (or “holes” which is kind of like the absence of an electron) in the material between the source and output are controlled by the gate’s electromagnetism. Electricity moves by these electrons/holes moving, so if we can stop them then the material becomes non conductive.
A FET has a input source of power, an output and a semiconductor between them. Next to the semiconductor is a “gate” that is connected to the input signal. The input signal controls the output’s connection to the input source.
When a voltage is applied to the gate sitting next to the semiconductor – either positive (p mode FET) or negative (n mode) – the electrons or holes in the semiconductor are essentially pushed aside and paralysed. So the semiconductor is turned “off” and power can’t flow from the source to the output. When the voltage is released the semiconductor turns back “on” as electricity can flow again.
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