I have a fairly strong understanding of how code like C is compiled into machine code and how transistors form gates which can be put together to compute lots of operations which can eventually become a computer. Say you have a machine instruction that says to add the contents of register 3 and register 5 and put the result in register 6. What is physically putting the voltages on the transistors in a way that achieves the desired result given that nothing is flipping a mechanical switch?
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The basic concept of a transistor used in digital devices is that it operates as a solid state switch. ELI5 It turns on and off and allows electrical connection between the transistor output and the supply voltage (for “high”) or ground (for “low”). If you connect the output of some transistor to the input of another transistor in specific configurations, you end up with basic logic gates.
Powering the CPU is to provide it with voltage and ground and that allows the transistors insided it to function.
Other transistors. It’s transistors all the way down. The moment power comes up from the PSU, all the transistors are initialized to their “default” state (either energized or not) simply by the path their gate electrodes have to the always-on power supply wires – through other transistors and components. From there they need some input to start changing states. That’s what the clock is for – when it got power, it automatically sent a pulse into the attached crystal and started trying to establish oscillation. When it is ready, it starts sending out the clock pulse to the rest of the circuits.
I’m not sure what you’re exactly asking so I’m just going to go over the process.
Power enters the computer through the Power Supply Unit. The PSU turns the wall outlets AC power into DC power and then steps down the Amps until it’s safe for the chips. The PSU plugs into the various components of the computer like the motherboard, Hard Drive, and cooling fans. T
he Motherboard then distributes the chips and logic circuits. In the chips, transistors are magnetized or demagnetized to change their conductivity.
The computer then starts reading every digit of the memory dedicated to register 3 and then alters register 6 to match. When it finds the terminator of register 3 it starts with register 5, reading every bit and changing the bits of Register 6 to match.
Transistors are like a three-layer semiconductor cake. Between two layers of one type of silicon is a “doped” layer that responds to external electrical excitation by admiting electron flow between the other two layers.
So when a transistor is connected across a voltage potential, no current flows. But if you apply a voltage to its third pin, current flows in proportion to the voltage applied to this third pin. Integrated circuits such as your CPU scale this component down to nanometer scale and repeat it millions of times to produce the transistor networks that machine languages can operate, and which assembly languages can control.
Quite literally, an electric signal directly determines if a transistor will pass current or not, which is super convenient, especially in computers where it’s function depends entirely on precisely organizing and controlling electrical signals.
Many types of transistors exist, some of which operate a little differently than I describe. But the essential point is that transistors let an electric signal control the flow of another electric signal.
Switches. Like the ones on a wall that controls the lights.
But much much smaller.
The voltage is always there; these switches, in the form of various components on a circuit board, route the needed power to the appropriate locations based on software instructions that determine how and when.
I assume you understand the basic function of a transistor.
A transistor is essentially a piece of wire that electricity can flow across. But it also has a third wire sticking out the middle of it, and depending on whether that third wire has a voltage applied, it “shuts off” the flow across the primary wire.
The way all computers function is that they are, rather simply, a *huge* mass of transistors arranged extremely cleverly. They are arranged in such a way that if you supply voltages into their input wires in an extremely specific pattern, they will cut each other off in a very precise, pre-planned way that results in a very specific pattern coming out the other end. Really, there is no “logic” being done here, it’s all hard-baked into the physical structure of the device. It will just naturally fall into that specific output when you apply the specific inputs based on its shape. All you have to do other than supply the inputs is supply power to the device.
So what something like a CPU *is*, is a carefully planned tangle of electricity pipes. They are meticulously designed with tons of foresight in such a way that, if you tickle the input pipes with voltage in a very specific pattern, all the transistors inside will add up and cancel out in just the right ways to cause a very specific, known output signal. Design your CPU with the ability to “understand” a whole range of inputs and you can create a very powerful computer. All you need is a list of magic patterns to feed into it one at a time that, when run in sequence, cause something useful to happen. AKA, code.
When you move the contents of one register to another, for example, what you’re doing is feeding into the processor the magic pattern that cause the transistors to freak out in just the right way that a perfect path of wires connecting the two registers together opens up. This will cause one register to take on the state of the other as the voltages equalize. The next instruction will close this pathway, trapping the voltage pattern in the register and thus locking in the new value. That physical path of wires connecting them continues to exist, but due to the clever design of the CPU, it’s always blocked by some mess of transistors, *somewhere*. The only way to fully open that particular path is to supply the magic combination that unlocks them.
The wires do. The wires are connected to the voltages. But there are also transistors in the way, which sometimes block the voltages, so that different voltages get to the wires.
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