Plan for Today

• Course Overview
• Computer Code
• Computer Hardware

Course Goals

• Demystifying Technology
• Technical Literacy
• Communication with Software Engineers

Course Overview

• Computer Hardware (~3 lectures)
• Introduction to Code (~5 lectures)
• Artificial Intelligence (~1 lecture)
• The Internet and the Web(~4 lectures)
• Human-Computer Interaction (~1 lecture)
• Security and Privacy (~2 lectures)
• Big Questions in Computer Science (~1 lecture)

Course Staff

Ashley Taylor ataylor4@stanford.edu OH: T/Th 4:20-5:30PM Gates 323

Shreya Shankar shreya@cs.stanford.edu OH: Weds 1-3PM Basement of Huang

Course Policies: Grade Breakdown

Course Policies: HW

• Weekly homework, out Tuesday/Thursday, due following Wednesday
• Combination of written questions and code exercises
• Two free 24-hour late days (pre-approved extensions)
  • Each late day covers 1 second to 24 hours late
• Submit on Canvas
• Short response paper on Artificial Intelligence
  • released week 5, due Friday, November 16

Course Policies: Honor Code

• Refer to the Stanford Honor Code
• All work must be in your own words.
• You may reference outside sources, but include a citation (e.g. URL link) at the end of your answer.
• The purpose of the homeworks is to assess your understanding of concepts; you must demonstrate that understanding to get credit.

Course Policies: Exams

Midterm

• Tuesday, October 30 in class
• Covers first five weeks of lecture
• Closed note, closed book, provided reference sheet

Final

• Monday, December 10, 8:30-11:30AM
• Covers the entire quarter; emphasis on material since the midterm
• Closed note, closed book, provided reference sheet

No alternate exams will be offered except for OAE and athletic conflicts.

Announcements

• Office hours will end a little early today (5:15PM); no OH on Thursday
• I will be at a conference for the rest of this week, so Thursday's lecture will be taught by Shreya
• Email Shreya with questions if you need a response before Sunday

Introduction to Computers

Applications

• Any program you run on your computer
• Microsoft Word
• Google Chrome
• Note application
• .exe (Windows) or .app (Mac) file
• Can use without knowing how it works behind the scenes (abstraction)
• Programs are written in code, the next layer of abstraction

Introduction to Code

Strengths of Computers

• Very fast (billions of operations per second)
• Very accurate

Weaknesses of Computers

• Literal
• Only simple operations
  • Addition
  • Comparison
  • Equality
• No insight

Introduction to Code:
How Computers Work

• Code is a series of instructions
• Each instruction is an operation
• Computer follows each instruction, one after another
• Programs are comprised of millions of instructions

Introduction to Code:
The Programmer

• Computers are hugely useful
  • Messaging
  • Image editing
• Programmers convert human ingenuity into computer code
• Develop algorithms (which we'll see later in the course!)

Introduction to Code:
Tips and Previews

• Code is like Legos - small bricks to big structures
• Patience :)
• Computers do exactly what you tell them
  (no interpretive power)
• We'll be doing green screen soon!
  

Introduction to Code:
First Code Operation

• Using Javascript (plus some extensions for 101)
• Each line of code is small
• First line: print!

Introduction to Code: Bugs

Story: named after a moth

Two types: syntax and logic errors

Introduction to Code: ASCII Art

We can use print statements to make art

Note: "\" is an escape character, so use "\\" if you want to print a slash

Programming Languages

• Code is written in a programming language
• Gives the "rules" (syntax and commands) for the code
• What programming languages have you heard of?
• Each has strengths and weaknesses and specializations (just like human languages)
• High-level (closer to how humans think) vs. low-level (closer to computers, but much faster)

Types of Programming Languages

• Compiled
• "Source code" (what the programmer writes) is converted to "object code" (what the computer reads)
• Compiled once, run many times (like translating a book to another language)
• Interpreted
• Machine code instructions generated on the fly (like acting as a verbal translator in a conversation)
• Slower to run, but no compile step!

Programming Languages: Source Code

• Source code is editable (what the programmer writes)
• .exe/.app files are just machine code
• Can't change a program without the source code!
• License is to use the software, not change it

Open Source in Theory

• Idea: give everyone the source code!
• No more licenses (free to use)
• Examples:
  • Programming languages
  • Browsers
  • Operating Systems
  • Compilers
• Championed by Richard Stallman
  • Free Software Foundation
  • Emacs, compiler, and more
  • Led to Linux

Open Source in Practice

• Give out source code (Github)
• Users have a right to modify the source code
• Users are incentivized to contribute back with changes
• Results:
  • Not a competitive advantage
  • Higher quality
  • Better use of resources

The Operating System

• Name types of operating systems?
• Starts running when the computer "boots up"
• Manager/supervisor
  • Starting/runs/stopping programs
  • Manages all shared resources (like memory)
  • No matter how a program ends, all resources must be released
• Can run multiple programs at once ("sandboxing")
• Allows a computer to change over time (updates)
• Other responsibilities:
  • File system
  • Manages windows
  • Some basic programs

Lifecycle of a program

• Load the program file from the file system
• Each program gets its own memory
• Program's code
• Data the program manipulates (like file being edited)
• OS "fetches" an instruction, which is then run (OS alternates instructions between programs)
• Begins with the first line of code
• Instructions like "return to step 5" keep the program running
• At the end of the program, OS needs to stop fetching instructions and ensure program returns memory

Ending programs

• Normal exit: user quits the program (e.g. by pressing "X")
• Abnormal exit: Program "not responding"
  • Use Activity Monitor (Mac)/Task Manager (Windows)
• "Illegal" activity: A program tries to access the memory of another program
• Out of Memory: A program requests more memory (e.g. you edit a lot of videos at once)

OS: Reboot

• Why does this fix anything?
• Sometimes some operating-system managed memory is not quite right
  • a bug in the operating system, or perhaps a hardware error
• A reboot wipes all the memory
• Starts up the operating system fresh
• Theoretically, never necessary (but in practice, a good approach)

Architecture: Machine Code

Architecture refers to the instructions sent by software that hardware can understand.

• Reminder: computer runs code instructions
• Each line of machine code is one operation
• Javascript is higher-level language
  • Have to translate Javascript to machine code
• Because of how hardware works (see Thursday's lecture), machine code is written in binary (1s and 0s)
• Machine-specific

Architecture: Assembly

mov    %esp,%ebp
sub    $0x28,%esp
mov    0x804d300,%eax
add    $0x1,%eax
mov    %eax,0x804d300
mov    0x804d300,%eax
cmp    0x8(%ebp),%eax

• Example
• Assembly is converted to machine code
• %esp, %ebp, etc. are in memory

Conclusion