3 ms·

So WHY are transistors important? How do you use them to create computers?

kragen 4y ago
https://nandgame.com/ https://nandgame.com/ will guide you through using NAND gates to create one computer. (There's lots more to learn about how to create other kinds of computers, and other ways of designing them, but walking through that one example should at least dispel the illusion of magic.) The last time I did it, it took me two hours, but I think that if you are coming at it without any previous knowledge of digital logic it should be tractable within about 40 hours. Then the only remaining things to understand are: ① how can you create NAND gates with transistors? ② why are transistors better for this than, for example, relays, pneumatic valves, or neon tubes, all of which would also clearly work? The answer to ① is actually pretty simple; the best explanation I've found is in The Art of Electronics, though Ken Shirriff's blog has a lot of great stuff on it too. And Falstad's circuit.js has some good simulations, like https://tinyurl.com/2eegeyxj https://tinyurl.com/2eegeyxj and https://tinyurl.com/ybpo5ls2 https://tinyurl.com/ybpo5ls2, which I think are nicely complementary to the theory. I've never seen a good explanation of ②, but I think the main answer is that electrons are about ten thousand times lighter than atoms, so with the same energy, they move about 100 times as fast. The result of that is that switches that work by moving around electrons can switch a great deal faster than switches that work by moving around atoms. Neon tubes also work by moving around electrons, but they're slower than transistors for a different reason: it takes the gas a long time to thoroughly deionize.
- remote_phone 4y ago
  Thank you for your response, in appreciate it! I will try out the link you gave me!
- djmips 4y ago
  The information moves faster than electrons move. It's shocking for slow individual electrons move!
  - kragen 4y ago
    That's true for information transmission, like what happens in wires, but as I understand it, switching in semiconductor diodes, transistors, and vacuum tubes actually requires the electrons to move in and out of depletion zones (or the vacuum). Switching in relays or pneumatic valves requires moving solid assemblages of atoms around instead. That's why it's slower, even though the drift velocity in the wires connected to a relay is the same as in the wires connected to a transistor.
    - djmips 4y ago
      Good points! It's true that switching times in transistors is a thing! There's even something called gate delay! I remember working on a system where 1 ns delays were available in a chain of transistor gates on the silicon die. You would do some tests and adjust the delay +/- by adding or removing a gate (selectable via some logic) and once you got the good results in your calibration you'd lock in the delay. This allowed for some synchronous signals when there was variation from different foundry processes and a variety of PCB layout distances between chips.
deleted 4y ago
[deleted]

https://nandgame.com/ https://nandgame.com/ will guide you through using NAND gates to create one computer. (There's lots more to learn about how to create other kinds of computers, and other ways of designing them, but walking through that one example should at least dispel the illusion of magic.) The last time I did it, it took me two hours, but I think that if you are coming at it without any previous knowledge of digital logic it should be tractable within about 40 hours. Then the only remaining things to understand are: ① how can you create NAND gates with transistors? ② why are transistors better for this than, for example, relays, pneumatic valves, or neon tubes, all of which would also clearly work? The answer to ① is actually pretty simple; the best explanation I've found is in The Art of Electronics, though Ken Shirriff's blog has a lot of great stuff on it too. And Falstad's circuit.js has some good simulations, like https://tinyurl.com/2eegeyxj https://tinyurl.com/2eegeyxj and https://tinyurl.com/ybpo5ls2 https://tinyurl.com/ybpo5ls2, which I think are nicely complementary to the theory. I've never seen a good explanation of ②, but I think the main answer is that electrons are about ten thousand times lighter than atoms, so with the same energy, they move about 100 times as fast. The result of that is that switches that work by moving around electrons can switch a great deal faster than switches that work by moving around atoms. Neon tubes also work by moving around electrons, but they're slower than transistors for a different reason: it takes the gas a long time to thoroughly deionize.

remote_phone 4y ago
Thank you for your response, in appreciate it! I will try out the link you gave me!
djmips 4y ago
The information moves faster than electrons move. It's shocking for slow individual electrons move!
- kragen 4y ago
  That's true for information transmission, like what happens in wires, but as I understand it, switching in semiconductor diodes, transistors, and vacuum tubes actually requires the electrons to move in and out of depletion zones (or the vacuum). Switching in relays or pneumatic valves requires moving solid assemblages of atoms around instead. That's why it's slower, even though the drift velocity in the wires connected to a relay is the same as in the wires connected to a transistor.
  - djmips 4y ago
    Good points! It's true that switching times in transistors is a thing! There's even something called gate delay! I remember working on a system where 1 ns delays were available in a chain of transistor gates on the silicon die. You would do some tests and adjust the delay +/- by adding or removing a gate (selectable via some logic) and once you got the good results in your calibration you'd lock in the delay. This allowed for some synchronous signals when there was variation from different foundry processes and a variety of PCB layout distances between chips.

deleted 4y ago

[deleted]