In this previous unit, Norm gave you an overall description of the Nand to Tetris journey. In this unit, we're going to focus on what we're going to do in this course, which is building a computer called Hack. So, here's the computer, in a very broad description, or sort of a diagram that captures only, some of its very main elements. It's going to have ROM, CPU, RAM and many other chips. And once we build this computer, we're going to connect it to a standard keyboard, and to a display unit. And at this point, you can start executing programs and enjoy the computer that you actually built. Which kind of programs? Well, anything that comes to your mind. You can write a program that plays Pong or a program that plays Space Invaders or Sokoban or, of course, Tetris. And these are actually examples of programs that were previously written by students. Who took this course. So, here's the general picture of this course and I'm basically repeating things that I know I've said before. We start with some general idea of the program that we want to write. We write the program, we compile it, we translate it further into machine language, we load the code into our computer. The computer is going to use all sorts of all sorts of chips that we built. Which are based on elementary logic gates and the whole thing ends up with the hardware itself. So basically what we did is we built a software hierarchy that sits on top of some hardware platform. And as Norm explained, we decided to split this enterprise into two different parts. The first part is called nand to Tetris part I and the second one which will be offered later is called nand to Tetris part II. And, in this particular course, we're going to focus on the hardware only, beginning at the very low level of the hardware itself, of electronics and and logic gates. And we're going to do it bottom up. So here we are at the very low level of of everything in, in applied computer science. And this actually is not computer science. This is electrical engineering and solid state physics, and so on. And all sorts of things that neither Norm and I understand much about. And therefore, we're going to obstruct the way this hardware and focus instead on the most elementary logic gate that we can think of, which is called Nand. You know, Nand is something that I can describe in ten seconds and I will do it in one of the following units, but for now. Let us assume that it's simply a basic, logic gate. We take this Nand gate, and from it, using a certain art called combinational logic, we're going to build a whole set of elementary logic gates like AND or Xor and so on. Then we'll take these gates and from them we are going to use both. Combinational logic and sequential logic, which is a different out of design, which takes into consideration times, and, and time and clocks, and from it we are going to build things like registers and RAM units, and and CPU. And then, we'll take this chip set that we built, and we'll design from it a full blown computer architecture called Hack. Now in order to write programs that can execute on this, on this machine and do it in a convenient way, we're going to also introduce an assembler into the picture and we're going to develop also an assembler for the Hack machine language. Now I've introduced all sorts of concepts that may sound very unfamiliar. Don't worry about it. Everything will be explained as the course progresses. Now, many of you are probably wondering, how are we going to actually build all these chips? Well, as it turns out, hardware engineers today don't do anything with their bare hands. They develop computers using computers. And in particular they use something called hardware simulator to design and test and debug the hardware that they want to build. And that's exactly what you will do also in this course. What we see here is a screenshot of our hardware simulator. A piece of software that you're going to download freely from our website. And the you're going to install it on your computer and you will do all the projects in this course using your computer and software that we will supply. So let us give you an example of how we are going to actually do it. Here's an example of Xor chip, which is one out of about 30 different chips that we're going to build in this course. And what you see here is an obstructed description of how Xor operates. So basically you're going to take this obstruction, think about it and. Along with all sorts of tips and guidance that we're going to provide. We'll come up with some logic diagram that enables you to build Xor using lower level gates, that you built before. Then you will take this diagram, and specify it using a language that we will teach you, which is called hardware description language. The result will be something called HDL program. You will take this HDL program. You will combine it with some test scripts that we that we will provide. And then you will debug, test, and complete your HDL program, using the hardware simulator that I described before. So that's what we're allowed to do with every one of the chips that we're going to build in this course. And the result is going to be the HAT computer. Now we're going to separate this journey into six different projects. So let me say a few words about every one of them. In the first week, we're going to build some elementary logic gates. 15 gates all together. As you see here in the slide. In the second week, we're going to build an arithmetic logic unit, an ALU, which is the centerpiece of the CPU that we'll build later. In the third week, we're going to build memory systems, you know, starting with registers and going all the way up to RAM and ROM units. In the fifth week we're going to take all the chips that, that we built so far and use it to design an actual computer. In week 4, before we build the computer we will write some programs in the Hack machine language in order to get, in order to get the feeling of what this computer is going to do, and in the last week in the course, we're going to introduce an assembler for the Hack machine language, and actually develop it in two different ways. One for people who have background in programming,. And one for people who don't. So these are all the projects that you're going to work on in this course and the result of your effort is going to be the Hack computer, a general purpose computer that can run any program that comes to your mind, Tetris and you know, practically anything else. Now, I'm sure that many of you are wondering, what do I have to know in order to take this course. Well, the answer is, we assume no previous knowledge whatsoever, in computer science engineering, or mathematics. All the necessary knowledge that is required to build the computer and to take this course. Is going to be supplied in the course itself. This is a self-contained course. You're going to learn a lot in seven weeks of exciting projects. So, this has been the unit in which we describe the journey from Nand to the Hack computer, and in the next unit we're going to overview the journey from Hack computer to Tetris.
