CS208 Introduction to Computer Systems
Monday, 27 March 2023
(Via Zoom because Jeff had COVID)

+ Hi!
- Welcome back
- Jeff Ondich, call me Jeff, Olin 301A

+ Today
- What's the course about?
- Logistics
- Using Visual Studio Code & mantis.mathcs.carleton.edu
- C basics

+ Layers of abstraction [hey Jeff: keep this to 10 minutes please]
- What's going on when I run a python program?

- Some layers
    Python program (hello.py)
            print('Hello, world')

    * Python interpreter (python3) written as a C program
        python3 hello.py
            [requests various services from the operating system.
                open a file, read from the file, write to
                standard output, etc.]

    * Assembly language version of python3 
  
    Machine language version of python3
    Data path ["computer architecture"]
    Digital logic components
    Transistors, other electrical components

    * [There's an "operating system" layer in there somewhere, too]

- This course 1991-2019: "how can you make a device that computes?"
    or "how do you organize a large pile of very simple electronic components
    into a computing device?" (i.e. a "computer architecture" course)
    (Lots of time at the "data path" and "digital logic" levels)

- This course 2019-present: what underlying computer system structures enable
    us to use a mid-level programming language (C), with typed local and global
    variables, dynamic memory allocation, function calls, etc.? (i.e. higher on
    the diagram, closer to your day-to-day experience as a programmer)
    (Lots of time at the C and assembly language levels)

- Benefits of the new version of the course
    - Closer to the concerns of day-to-day programming life
    - Insight into computer security
    - Insight into performance issues
    - Like the old version, this stuff is super-cool

- General goal: tell the story of what happens when you compile and run a C program
- Persistent theme: how is computer memory structured and used?

+ Rough plan
- The C programming language, including pointers
- Data representation
    how are integers, real numbers, and characters stored in memory and on disk?
- x86_64 assembly language
    - what is the assembly layer mental model? what operations are available?
    - how do C structures get implemented in assembly language?
    - debugging assembly code with gdb (the "GNU debugger")
    - reverse engineering compiled code
    - buffer overflow attacks
- the process and threads models; how the OS supports multi-programming
    (and why it turns out to be painful)
- networking via the sockets model

+ Logistics
- Course website
- Upper-right menu on course website
    - Info (general information about the course)
    - Resources
    - Samples (pay attention! study! ask questions!)
    - Office Hours
    - Jeff (my Carleton home page)
- Moodle: homework submission and quizzes
- Slack (#announcements, #questions, etc.)

+ Masks, illness, etc.
- Who knows what will happen this term?
- Zoom will be available if you're ill and you let me know
    - Use the "office hours" Zoom link
    - It won't be ideal, but I'll mostly try to stay on-camera
- Please mask if you have a cold while attending class
    I will do the same

+ Getting started: Unix, VS Code, C
- Resources for learning more Unix: "Resources" link on course page
- Resources for learning C: "Resources" link on course page
- Sample programs: "Samples" link on course page.
    ** I expect you to study and play with these samples.
    Ask questions!
- Doing your work on mantis.mathcs.carleton.edu
- VS Code, remote editing, and an integrated terminal
- First assignment: a couple small C programs
- Second, bigger assignment: implementing queues

+ Short break
- Introduce yourself to somebody you don't know. Get each other's
pronunciation right. Book/movie/hometown/whatever.

+ C
- C experience unevenly distributed: if you're taking 208
    before 251, you'll be happy when you take 251
- hello.c (comments, variables, printf)

+ Visual Studio Code + mantis.mathcs.carleton.edu
- Demo & pointer to lab

+ More C
- character_counter.c
    loops, conditionals, functions, comparison to Java
    types: char, int, float, double
    file I/O
- strings.c

+ Slightly weird C, relevant for the first assignment
- arrays2d.c


+ Next
- More C, focus on pointers
- Queue implementation assignment (lotsa pointers!)
- Integer notations: binary (0b), octal (0), decimal, hexadecimal (0x)
- Data representation: integers, characters, real numbers, strings



+ For your homework
- character_counter.c as a template for depunctuate.c
- arrays2d.c as a template for sorter.c