From a NAND Gate To Tetris

mikejuk writes "Long before the current crop of MOOCs (Massive Online Open Course) there was a course that taught you all you needed to know about computers by starting from the NAND gate and working its way up through the logic circuits needed for a computer, on to an assembler, a compiler, an operating system, and finally Tetris. Recently one of the creators of the course, Shimon Schocken, gave a TED talk explaining how it all happened and why it is still relevant today. Once you have seen what is on offer at http://www.nand2tetris.org/ you will probably decide that it is not only still relevant but the only way to really understand what computers are all about."

Comments

NAND Gate

[zippo01]

I watched this video and it really does seem like it would be a fun course! I'm not really sure about the whole God giving man NAND. Though that is prolly why my belief in God is 11. Hah, what a crappy NAND joke.

Logic is Logic

[thejuggler]

Somewhere between learning to write my first "Hello World" program on the Apple IIe (and the TI99/4A) and making a career out of programming years later, I went to schools for Computer Repair and Bio-Medical Electronics. I still have a pile of 7400 series IC chips and my breadboards amongst other electronic components. I learned analog and digital circuit design in the late 80's. The logic learned in those classes still applies to everyday programming today. No matter what I did in those previous careers, the training I did then still applies today. AND, OR, NOT, NAND, NOR, XOR and XNOR are still the 7 basic logic elements that make up all digital electronics and programming. From there Truth Tables are built and boolean algebra is applied to create any and all circuits and code today. In my humble opinion these are still essential to training people new to various IT fields. It's like having to learn nous, verbs, adverbs and adjectives in order to write understandable thoughts. If you lack this basic understanding learning the more advance concepts is difficult at best. It's good to see these are still being taught somewhere.

Re:Logic is Logic

[dkf]

AND, OR, NOT, NAND, NOR, XOR and XNOR are still the 7 basic logic elements that make up all digital electronics and programming.

Actually, real digital circuit design uses rather more elements than that, some of which can't be derived from those ideal elements either. Even excluding the clock generator (a thoroughly analog component in its core) there's still some really strange things you can usefully do with transistors that just won't model as anything simpler; my favorite is the arbitrator, it determines which signal rose (or lowered) first and which is used to connect together parts of a chip that use a common power supply but unsynchronized clocks. Simplistic digital theory says it can never work, but in reality it's very effective (and it depends on the fact that transistors are analog devices with some quantum mechanical behavior for disambiguating in the tricky cases. Mad, fun, mad fun!)

Re:Logic is Logic

[sFurbo]

You have 2 inputs that can each be 1 or 0, so there are 4 different inputs. For each of those, you have 2 possible outputs, so there are 2^4=16 different truth tables.

Of these, 8 are symmetrical in A and B (gives the same output for input (1,0) and (0,1)). Theses are AND, OR, NAND, NOR, XOR, XNOR, TRUE and FALSE

The remaining 8 are 4 sets of duplicates (if you switch A and B, we call the gate the same name). These are A, not-A, A AND NOT-B, and its negation, NOT-A OR B. The two last does not seem to be standard gates, so no, there are, in fact, two more non-trivial truth tables for two inputs.

Re:Logic is Logic

[famebait]

No, but it sums up all the useful/practical ones.
If you only have two inputs, there are only 4 rows in the table,:
| A | B |
| 0 | 0 |
| 0 | 1 |
| 1 | 0 |
| 1 | 1 |

This yields only 16 possible output columns:
0000 - does not vary with input
0001 - AND
0010 - not commutative
0011 - reacts only to A
0100 - not commutative
0101 - reacts only to B
0110 - XOR
0111 - OR
1000 - NOR
1001 - XNOR
1010 - reacts only to B
1011 - not commutative
1100 - reacts only to A
1101 - not commutative
1110 - NAND
1111 - does not react to input

That makes 6 potentialy desirable operations. The seventh is NOT, which takes only one input.
The not commutative ones could conceivably be put to useful work, but in physical designs the asymmetry is impractical, and you can trivially construct them from other gates if need be. In fact some of the useful ones ar also usually constructed from combinations of the others, and all of them *can* be constructed from combinations of NAND gates.

Re:Bottom Up Approach

[Anonymous Coward]

Your reply just made Donald Knuth cry.

Sometimes you need to learn a generic and simplified technology before you can comprehend the incredibly complex and optimized real world examples. And sometimes real world examples are so narrowly designed that you would lose out on a general understanding of computing by focusing on that one design. Finally, sometimes real world examples carry the baggage of the past which can waste valuable time.

Re:Cue the "real programmers' jokes

[Rockoon]

I'm not saying its a good idea to develop an elitist attitude towards the people that use them, but this explains why there's some rational basis for looking down on scripting languages. It's not that they are inherently bad or that the people who use them lack the ability to do 'real programming'. But, they are basically all about not having to know anything at all about how the other layers of abstraction work, and a consequence is they also don't give the programmer any real connection to how the hardware layer works and how you get from it to what they know.

The same argument could be used against C++, or C, and not just scripting languages like you claim. I know that most C programmers think they are doing low level programming, but they aren't.

For example, if you know how an OS is generally compiled in a language such as C or C++, then the next step is understanding that the compiler is itself running 'on a level above' assembly language. Understand that, and its a straightforward conclusion that a program can always be written in assembly that bypasses ANY controls the OS has about accessing different parts of memory, doing file copying, assigning user and admin permissions, and similar things.

Umm, no. Just no. I have a great idea.. when you don't know what you are talking about, don't fucking talk. We both know that you don't know what you are talking about, which leads to the conclusion that you like to pretend to know what you are talking about... in short, you are a dishonest fuck.