Building a 4 bit computer from Transistors | Hacker News Reader

Building a 4 bit computer from Transistors

waitingforfriday.com

56 pointsdholowiski15 comments

Lots of comments denigrating this demonstration. I'd like to say that as someone who understands some fundamental things like AND/NOT/OR etc only at a high level, its very illuminating to see how the math is implemented in hardware.

You have to remember that 30-40 years ago people were building entire businesses building computers by knowing this stuff and wiring everything together by hand. Many younger folks now have little to no idea how the devices they use every day work at a fundamental level, and its videos like this that could let a young hacker-to-be pick up a few parts inexpensively and easily wire up their own basic logic circuits. Its this kind of hands-on education that helps curious people learn and explore.

Well, 30 years ago was 1981 and the IBM PC was kicking off that part of history. 40 years ago was 1971. There were still many commercial transistorized systems but most new designs were going to integrated circuits quickly.

This http://en.wikipedia.org/wiki/IBM_1401 is probably a representative example of the transitorized computer, produced from 1959 to 1971. It's a good bet that the people who designed it knew how to solder but were different from those who assembled it. They knew the transistors, but probably designed it in terms of higher-level blocks of logic (adders, memory, etc).

Not many people have designed and built full computers from scratch at the transistor level. Enthusiasts didn't really get into it until microprocessors were available. Even then, they required hundreds of solder connections to be able to even use lights and switches for IO.

Fun times.

NAND to Tetris -- build your own computer system from NAND gates on up to your own Object Oriented language, operating system, and simple games.

Just doing this one course to tie together a Computer Science education puts you a step ahead of 50% of the coders out there.

http://www.catonmat.net/blog/video-lecture-from-nand-to-tetr...

When I was a kid, my hero was David L. Heiserman. http://www.beam-wiki.org/wiki/Heiserman,_David_L. His book "Build Your Own Working Robot" (ISBN 0-8306-6841-1) I must have read a hundred times.

It wasn't quite as low as transistor logic, but it was designed from discrete logic gates.

I also remember him writing "How to design & build your own custom TV games", which was basically NAND to Pong, without a CPU.

What‽ It isn't even Turing complete.

How about a 16 bit computer made from 3000 transistors[1] that runs at 500kHz? http://www.6502.org/users/dieter/mt15/mt15.htm

[1] umm, and a couple 74 series chips to generate the clocks and buffer the busses.

"Code: The Hidden Language of Computer Hardware and Software" by Charles Petzold does an excellent job of explaining everything (from logic gates to CPU architecture to graphics) to the layperson. If any nontechnical person (my dad, for example :p) asked me how computers worked, I would tell him/her to read this book.

Even for a technical reader it's still an enjoyable book. It inspired me to design and make a computer of my own.

Calling this a computer is rather misleading- it's really a 4-bit adder.

Let's give this guy credit where due. It's probably the most awesomest transistorized 4-bit adder handmade in the US since 1973.

I will say it's a very clean build and a nice writeup.

Thanks, I've been looking for a good tutorial on this for a while. Going to try to implement this in Minecraft (it's funny how Minecraft has incidentally made circuitry easier to get into).

Lots of half-gates means lots of pulldown/pullup resistors. Probably uses a ton of power (per bit, or whatever.)

We had to build a full 16-bit machine in school. Thankfully, we were allowed to use 290x ALU slices.

Site's down for me - has it been slashdotted by HN? (so to speak)

This is a dumb 4-bit adder, something every CS student builds using breadboards, in a middle of some Digital Logic course.

Perhaps in some schools, and perhaps in some courses, but not usually with transistors.

Well they would have played with a javascript simulation of a half-adder, or at least seen a youtube video of a powerpoint presentation describing it - that's good enough for CS these days.

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