CS31: Introduction to Computer Systems
Fall 2018

Class Info | Schedule | Lab Sessions | Ninjas | Tips for Success
Grading | Academic Integrity | Academic Accommodations | Links


  • The CS department system administrators / ninjas will be hosting two using Unix info sessions in SCI 256 from 7:00 PM - 8:00 PM on Monday and Tuesday of week 1. They're open to everyone, but if this is your first class in the Swarthmore CS department, you should attend one of these.

Class Info

Class: TuTh 1:15–2:30, Science Center 199
Professor: Kevin Webb
Piazza: Q&A Forum
GitHub: Swarthmore GitHub Enterprise
Gradesource: Grade listing
Office: Sci 255
Office hours (Kevin): Mo 12:30–2:00, Th 2:45–4:00, or by appointment
Office hours (Scout): Mo 2:00–3:30, Th 10:30–11:30, or by appointment

This course is a broad introduction to computer science that focuses on how a computer works and how programs run on computers. We examine the hardware and software components required to go from a program expressed in a high-level programming language like C or Python to the computer actually running the program. This course takes a bottom-up approach to discovering how a computer works, and introduces parallel and distributed computing with a specific focus on parallelism for multicore and other shared memory systems. Topics include theoretical models of computation, data representation, machine organization, assembly and machine code, memory, I/O, the stack, the operating system, compilers and interpreters, processes and threads, and synchronization. In addition to parallel programming, we will discuss parallel computers and system-level support for parallel computing. Prerequisite: Completion of CS21 or its equivalent.

The course is composed of the following:

Textbook & Clicker:

This course will use iClickers to facilitate feedback and discussion during class. Clickers may be purchased at the college bookstore or online. Please register your device as soon as you get it. Registering allows me to give you credit for quizzes and class participation. We will begin using clickers for credit at the start of week 2!

Rather than requiring a textbook, we're going to use readings from the web as our introduction to new material. The textbook we've used in the past for this course is: Computer Systems: A Programmer's Perspective by Bryant and O'Hallaron (Second edition: 2/E CS:APP2e). It's a great reference, and I recommend it as a supplemental source of information, if you're interested. I will list corresponding sections for this book, when applicable.

Goals for the course:

By the end of the course, we hope that you will have developed the skills to:


This is a tentative schedule; it may change as we go. You should read the assigned sections before class to prepare for the reading quiz. All section numbers refer to the Bryant and O'Hallaron textbook unless otherwise indicated.


Sep 04

  Course Introduction
No reading

Sep 05

  Lab, Week 1 Lab 1 Audio

Sep 06

  Data Representation
Reading: This page
Textbook (supplemental): 2.1 - 2.1.3, 2.2 - 2.2.3

Sep 11

  Binary Arithmetic
Reading: This page
Textbook (supplemental): 2.1.8, 2.1.10, 2.2.3, 2.3 - 2.3.1

Sep 12

  Lab, Week 2 Lab 2 Audio

Sep 13

  Introduction to C Programming
Reading: C for Python Programmers (Sections 1.5-2.5)

Sep 18

  Digital Circuits
Reading: Page 1 and Page 2
Textbook (supplemental): 1.4.1, 4.2 - 4.2.4

Sep 19

  Lab, Week 3 Lab 3 Audio

Sep 20

  Digital Circuits, Continued
Reading: This page and the sections titled "Arithmetic logic unit", "Signals", and "Circuit operation" of this page.
Textbook (supplemental): 4.2.5

Sep 25

  ISAs and Assembly
Reading: From this PDF, The introduction (first page) and sections 2.2, 2.3 - 2.3.3, 2.5.0 (don't continue into 2.5.1)
Textbook (supplemental): 3.0, 3.2

Sep 26

  Lab, Week 4 Audio

Sep 27

  ISAs and Assembly, Continued
Reading: X86 Assembly (Intro through "Registers" section), Addressing modes (Just the intro here / stuff above table of contents), and Branching
Textbook (supplemental): : 3.4 - 3.4.2, 3.6 - 3.6.4

Oct 02

  Pointers and Memory
Reading: The 5-minute guide to C pointers

Oct 03

  Lab, Week 5 Lab 4 Audio

Oct 04

  Pointers and Memory, Continued
Reading: Pointer Arithmetic (skip "Two dimensional arrays" and "Pointer subtraction") and malloc & free
Textbook (supplemental): 3.5.1, 3.8.2, 9.9.1 - 9.9.2, 9.11 - 9.11.2, 9.11.7 - 9.11.10

Oct 09

  Functions and the Stack
From this page, the intro through the "Structure" sections. (You can skip 'enclosing subroutine context' and 'lexically nested routines'.)
Textbook (supplemental): 3.7 - 3.7.3
Note: The textbook draws memory upside down as compared to how we draw it in class!

Oct 10

  Lab, Week 6 Lab 5 Audio

Oct 11

  Functions and the Stack, Continued
Reading: From this page, read about the call and ret instructions and the subsequent "Calling Convention" section (scroll down a little).

Oct 16

Fall Break

Oct 17

Oct 18


Oct 23

  Arrays, Structs, and Pointers
Reading: page 1, page 2, and the intro of page 3.

Oct 24

Midterm exam 7:00 PM - 8:30 PM in SCI 101

Lab, Week 7 - Midterm Q&A / Work on Maze Audio

Oct 25

  Arrays, Structs, and Pointers, Continued
No reading quiz. Review the previous readings.

Oct 30

  Storage and the Memory Hierarchy
Reading: this page and through "spatial locality" on this page.
Note: These pages are a work in progress. The links on the sidebar won't work and figures/tables aren't officially labeled yet. Please let me know if you catch any typos or have feedback about improving these sections!

Oct 31

  Lab, Week 8 Lab 6 Audio

Nov 01

Reading: Through "Memory Address Division" on this page
Textbook (supplemental): 6.3 - 6.4.4

Nov 06

  Caching, Continued
Reading: Everything after "Memory Address Division" on this page.

Nov 07

  Lab, Week 9 Lab 7 Audio

Nov 08

  Operating Systems
Reading: this page

Nov 13

Reading: this page, up to the first exercise.

Nov 14

  Lab, Week 10 (Same page as week 8) Lab 8 Audio

Nov 15

  Virtual Memory
Reading: this page (through "paging")
Textbook (supplemental): 9.0 - 9.2, 9.5, 9.6.0

Nov 20

  Virtual Memory, Continued
Reading: this page ("virtual and physical addresses in page systems" through "paging implementation")

Nov 21

  Lab, Week 11 Audio

Nov 22



Nov 27

  Parallel Applications and Threading
Reading: The Concurrency Revolution (Note: this article is from 2005)

Nov 28

  Lab, Week 12 Audio

Nov 29

  Race Conditions and Synchronization
Reading: this page, Intro through "multithreading" and this page, Intro
Textbook (supplemental): 12.4 - 12.5.3
Lab 9 Audio

Dec 04

  Race Conditions and Synchronization, Continued
Reading: this page, Intro through "necessary conditions"
Textbook (supplemental): 12.7.4 - 12.7.5

Dec 05

  Lab, Week 13 Audio

Dec 06

  Deadlock Audio

Dec 11

  Parallel Programming with pthreads
Buffer Overflows

Dec 15

Final Exam, 9:00 AM - 12:00 PM (Science Center 101)

Lab Policy

This course features regular lab assignments that account for the largest component of your course grade. Lab attendance is required by all students, unless you have already completed and submitted the lab assignment for the week. Additionally, the cs labs are open 24 hours a day, 7 days a week for you to use for CS31 lab assignments. While you must attend the lab session for which you are registered, you may optionally attend additional lab sessions, provided space is available. In case of space constraints, students registered for the lab will have seating priority.

Lab assignments will typically be assigned during the lab sections on Wednesday will generally be due by midnight on Tuesday, one week later. You are strongly encouraged to start early!

Even if you do not fully complete an assignment, you should submit what you have done to receive partial credit.

Weekly Lab Sessions
Section A Wednesdays 8:50—10:20 Clothier 016
Section B Wednesdays 1:15—2:45 Clothier 016
Section C Wednesdays 3:00—4:30 Clothier 016

Accessing the CS labs after hours

You can use your ID to gain access to the computer labs at nights and on the weekends. Just wave your ID over the onecard reader next to the lab doors. When the green light goes on, just push on the door handle to get in (the door knob will not turn). If you have issues with the door locks, send an email to local-staff@cs.swarthmore.edu. If the building is locked, you can use your ID to enter the door between Martin and Cornell library. For this class, your ID will give you access to the labs in rooms SCI 238, 240, 256, and Clothier basement.


The CS 31 Ninjas are student mentors who will assist in class/labs and run evening study sessions. You are encouraged to participate in Ninja evening study sessions to get friendly assistance on lab assignments and help with preparing for exams.

Weekly Evening Ninja Session: Sundays, 7:00 PM - 11:00 PM

The CS 31 Ninjas:   Greg, Jessica, Kei, and Sally

Ninja Coordinator:   Lauri Courtenay (SCI 257)


Grades will be weighted as follows:
35%Lab assignments
30%Final Exam
25%Midterm Exam
  5%Reading Quizzes (I will drop your three lowest quizzes.)
  5%Class Participation

Absence / Assignment Extension Policy

For CS 31, we will drop your three lowest reading quizzes and participation grades. Dropping these scores is intended to help when you need to miss a class due to a minor illness or to travel for an interview. You are still responsible for the material, and you should review any missed materials via the class recordings as soon as you can.

You must submit your assignments electronically by pushing to your assigned git repository. You may push your assignment multiple times, and a history of previous submissions will be saved. You are encouraged to push your work regularly.

To help with cases of minor illnesses, athletic conflicts, or other short-term time limitations, all students start the course with two "late assignment days" to be used at your discretion, with no questions asked. To use your extra time, you must email your professor after you have completed the lab and pushed to your repository. You do not need to inform anyone ahead of time. When you use late time, you should still expect to work on the newly-released lab during the following lab section meeting. The professor and ninjas will always prioritize answering questions related to the current lab assignment.

Your late days will be counted at the granularity of full days and will be tracked on a per-student (NOT per-partnership) basis. That is, if you turn in an assignment five minutes after the deadline, it counts as using one day. For partnered labs, using a late day counts towards the late days for each partner. In the rare cases in which only one partner has unused late days, that partner's late days may be used, barring a consistent pattern of abuse.

If you feel that you need an extension on an assignment or that you are unable to attend class for two or more meetings due to a medical condition (e.g., extended illness, concussion, hospitalization) or other emergency, you must contact the dean's office and your instructors. Faculty will coordinate with the deans to determine and provide the appropriate accommodations. Note that for illnesses, the College's medical excuse policy, states that you must be seen and diagnosed by the Worth Health Center if you would like them to contact your class dean with corroborating medical information.

How to Succeed in CS 31

Academic Integrity

Academic honesty is required in all your work. Under no circumstances may you hand in work done with (or by) someone else under your own name. Your code should never be shared with anyone; you may not examine or use code belonging to someone else, nor may you let anyone else look at or make a copy of your code. This includes, but is not limited to, obtaining solutions from students who previously took the course or code that can be found online. You may not share solutions after the due date of the assignment.

Discussing ideas and approaches to problems with others on a general level is fine (in fact, we encourage you to discuss general strategies with each other), but you should never read anyone else's code or let anyone else read your code. All code you submit must be your own with the following permissible exceptions: code distributed in class, code found in the course text book, and code worked on with an assigned partner. In these cases, you should always include detailed comments that indicates on which parts of the assignment you received help, and what your sources were.

Failure to abide by these rules constitutes academic dishonesty and will lead to a hearing of the College Judiciary Committee. According to the Faculty Handbook: "Because plagiarism is considered to be so serious a transgression, it is the opinion of the faculty that for the first offense, failure in the course and, as appropriate, suspension for a semester or deprivation of the degree in that year is suitable; for a second offense, the penalty should normally be expulsion."

The spirit of this policy applies to all course work, including code, homework solutions (e.g., proofs, analysis, written reports), and exams. Please contact me if you have any questions about what is permissible in this course.

Exam Integrity

Students must strictly adhere to the following policy, which applies to all exams taken in a Computer Science course at Swarthmore:

Exam takers must place all non-essential items at the front of the room (or other designated area). Unless otherwise permitted, students may not have any electronic devices or course materials in their possession during the entirety of the exam. This includes cell phones, tablets, laptops, smart watches, course notes, articles and books, among others. These items should be placed at the front of the room near the proctor. If you need to leave the room during the exam, you must obtain permission from an instructor first. Any non-permitted discussion or aide in regards to exam material will result in immediate forfeiture of the exam and a report to the College Judiciary Committee. Please discuss any concerns or accommodations with your instructor prior to starting the exam.

Academic Accommodations

If you believe that you need accommodations for a disability, please contact the Office of Student Disability Services (Parrish 113) or email studentdisabilityservices@swarthmore.edu to arrange an appointment to discuss your needs. As appropriate, the office will issue students with documented disabilities a formal Accommodations Letter. Since accommodations require early planning and are not retroactive, please contact them as soon as possible. For details about the accommodations process, visit the Student Disability Service Website.

You are welcome to contact me privately to discuss your academic needs, but all disability-related accommodations must be arranged through the Office of Student Disability Services. To receive an accommodation for a course activity you must have an official Accommodations Letter and you need to meet with me to work out the details of your accommodation at least two weeks prior to any activity requiring accommodations.

Links that are related to the course may be posted here. If you have suggestions for links, let me know.