Why are volts used as bits in a computer and not charges? How do we read volts, write volts, etc.? Wouldn’t using charges be much simpler?
In: Technology
You could see it as volts themselves not existing. Voltage is a measure of how much electrical energy potential is present in a point in comparison to another, and that potential is due to an accumulation of charge in a point. Modern memory technology uses capacitors in parallel with transistors to store ones and zeros. It’s not that we store 3 Volts on a capacitor, we charge them up to a potential of 3 Volts. How do we “read” volts? By the effect the have on the circuit: if a transistor is in a conducting state, it is because there is a charge inducing a voltage on it. How do we write them? We connect the capacitors directly to the energy supply to let them charge up. Not so ELI5, but hope it helps a bit (pun not intended).
Its volts or lack of that makes up information, live for on dead for off, so a 1 is on and zero is off, thats basically how zeroes and ones are held in a computer.
If variable charge was used it could be mis interpreted what value was being used because electricity is not always 100% reliable to charge up to a point and not further.
There is a very good and easy to understand video relating to this
[here](https://youtu.be/fXwSFhUVFmE)
If a modern computer that would not work because you control the metal–oxide–semiconductor field-effect transistor (MOSFET) with the gate voltage.
What you control is the current flow between the source and drain with the gate voltage. So you have a voltage controlled current switch. In a ideal transistor there no current flow from the gate to the source or drain.
Electronically the gate is like a capacitors connected between it and the drain and source. The voltage it has will depend on the number of extra electrons it have in it. You could look at it as charge control but that make it harder since the capacitance of the gate, the wires through differs between different transistors.
Because voltage, current and other electrical parameters of the system in interconnected you could think of it as control by the amount of charge at the transistor gate but that make it a lot more complicated model.
What you do in digital logic is to have the gate at 0 V or at the supply voltages so the current through the transistor is zero or maximum. The max current will charge up the capacitor in the wires and gates of other transistors and increase the voltage to control the. You do the same with transistors connected to the ground but then you drain the electrical charge.
In older bipolar junction transistor (BJT) the current into the base control the current flow between the collector and emitter. For them looking at is as current controls make more sense but they are not used for CPUS today as it would use a lot more power.
If FLASH memory the data is stored as a electrical charge in a floating-gate MOSFET. So data is stored as trapped charge that result in a voltage. So you can say that data is stored as electrical charge but at the same time they produce a voltages because of the interconnection.
It is more difficult to control a charge and be as precise with current, controlling its flow to a point of electrical accuracy. It is much simpler to use on or off voltage schemes.
Measuring voltage is measuring charges
You can count bonus electrons one of two ways. You can run them through an Ammeter and see what current you got which will tell you how much total charge flowed, or you can use a voltage meter to measure the voltage created by the charge.
Measuring your charges by measuring the current moves them from their source and destroys the original data so this isn’t good.
Measuring voltage does not corrupt the original charge grouping so you can measure it multiple times and still have the same value, this is good.
When you’re dealing with something like RAM cells, measuring voltage pretty directly measures charge, they’re just off by a scale factor (capacitance). We measure the voltage to see if its above a certain threshold, and if it is then we feed the High level voltage to the rest of the circuitry.
For MOSFET based logic circuitry, you don’t actually care about charges at all. Its completely voltage based. Did you apply enough voltage to turn on the transistor? Yes? Great, its going to turn on the downstream ones. You could look at gate charge, but gate charge varies depending on the size of the transistor while voltage is constant and what really determines the behavior of the transistor
All of our logic circuitry was built around using and measuring voltage because its easy and non-corrupting of the original data. You could make a system that worked on measuring charge and current using some BJT based logic, but you would likely have high power consumption. We use a CMOS layout in modern ICs because circuit blocks that aren’t switching use effectively zero power.
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