CSE 421/521 Spring 2016

This web page serves as the syllabus for the course.

1. Overview

This course is an introduction to operating system design and implementation. We study operating systems because they are examples of mature and elegant solutions to a difficult design problem: how to safely and efficiently share system resources and provide abstractions useful to applications.

For the processor, memory, and disks, we discuss how the operating system allocates each resource and explore the design and implementation of related abstractions. We also establish techniques for testing and improving system performance and introduce the idea of hardware virtualization. Programming assignments provide hands-on experience with implementing core operating system components in a realistic development environment.

2. Evaluations



Response Rate (%)


Instructor Rating (out of 5)


Course Rating (out of 5)


Full evaluation results are available here (PDF). Note that this year we rolled out the new test161 OS/161 automated testing framework. This had the result of making the assignments more challenging, particularly for the undergraduates enrolled in the course. We plan to address this issue in future years. However, due to ongoing curriculum revisions we anticipate that operating systems will no longer be a required course for undergraduates within a few years. At that point the difficult level may prove appropriate for a self-selected group of students.

3. Information

3.1. Course Staff

  1. Instructor: Geoffrey Challen. I go by "Geoff", "Geoffrey", or "GWA"—not "Dr", "Professor, or "Sir". Please use prof@ops-class.org to aid my email filtering. However, you should rarely contact me directly. Instead, 99% of the time use the Discourse forum or 1% of the time contact the entire staff at staff@ops-class.org.

  2. Teaching Assistants: Ali Ben Ali and Xu Zhen are your fantastic and hard-working teaching assistants this semester. They will be teaching recitation, holding office hours, and grading exams. Please do not email them directly—​instead, use Discourse or email staff@ops-class.org for a faster reply.

  3. Ninjas: In addition to the official TAs, we have a number of volunteers from my research group blue as well as returning 421 Spring 2015 students. This year’s ninjas are Yihong Chen, Dan Conway, Scott Haseley, Carl Nuessle, Gela Malek Pour, Guru Prasad, Isaac Reath, Benjamin Rueda, Jinghao Shi, Mark Simpson, and Yousuf Zubairi. Ninjas will hold office hours but do not do any grading.

3.2. Times and Locations

  1. Lecture: MWF 2:00–2:50PM, Knox 104.

  2. Recitations: T 4:00–4:50PM, NSC 222; and F 8:00–8:50AM, Knox 04. Recitations will be taught by Ali. Attendance is not mandatory, and you can attend either or both depending on what fits your schedule. Graduate students may only attend recitations if there is space 1.

  3. Office Hours: We have 20 total and 41 person-hours of office hours scheduled this semester. Please come and join us in Davis 301B! Office hours are a fun place to do the assignments and just hang out with each other and the course staff. Don’t wait until you have a problem to come!

3.3. Exams

An ungraded pre-term exam will be given in class on Wednesday 1/27/2016. The 50-minute midterm will be given in class Wednesday 3/23/2016. A 3-hour final exam will be Monday 5/9/2016 from 3:30—​6:30PM in Knox 104. Please contact the course staff as soon as possible if you cannot attend a scheduled exam for any reason.

3.4. Undergraduate Prerequisites

4. Description

Operating systems are the masterworks of the programming world: beautiful and sophisticated solutions to difficult design problems that have emerged from years of effort by thousands of skilled programmers. Just like budding artists study the works of the great masters for inspiration, we programmers study operating systems. While most of you will never contribute a single line of code to a production operating system, we hope that by the end of the course you will have learned something from their elegance and maturity.

Understanding operating system design will make you a better software engineer, and struggling with operating system programming will make you a better programmer. This course gives you a chance to do both. We establish a conceptual track through lectures and exams, where we discuss the concepts and design principles of modern operating systems and how hardware devices such as the CPU, memory, and disks are multiplexed and abstracted. Equally important, however, is the programming track which proceeds through four assignments that give you the chance to implement core operating system functionality in a simplified development environment. After studying synchronization, you will implement synchronization primitives. After studying the system call interface, you will implement it. After studying virtual memory and address translation, you will design and implement a virtual memory subsystem.

Designing and implementing operating system concepts is not easy, and neither is this course. But we are here to help and committed to providing you with the support you need to succeed. Our online grading tools provide helpful feedback and allow you to repeatedly test and submit your assignments until you earn the grade you desire. And our TAs are experienced and will be available for many hours each week to provide individual help. We expect that you will find this course difficult, but we hope you will also learn a large amount, have fun, and develop a passion for computer systems.

4.1. Learning Objectives

4.1.1. Conceptual Objectives

When you finish this course, you will be able to:

Outcome Assessment

Understand the abstractions supported by modern operating systems.

Class and recitation participation, midterm, final exam. 70% correctly identified marks outcome achieved.

Describe how operating systems safely and efficiently multiplex hardware resources through effective policies and mechanisms.

Analyze the designs and features of historical, current, and emerging operating systems.

4.1.2. Programming Objectives

When you finish this course, you will be able to:

Outcome Assessment

Design and implement working systems software.

Office hours attendance, homework and programming assignments. 70% correctly identified marks outcome achieved.

Identify and correct bugs in complex, multithreaded systems.

Formulate and test performance hypotheses.

4.2. ABET Outcomes

The Accreditation Board for Engineering and Technology (ABET) helps guide curriculum by defining common outcomes that coursework should help students achieve by the time they graduate. This course should assist you in four of the nine University at Buffalo outcomes:

  1. (c) An ability to design, implement and evaluate a computer-based system, process, component, or program to meet desired needs.

  2. (d) An ability to function effectively on teams to accomplish a common goal.

  3. (f) An ability to communicate effectively with a range of audiences.

  4. (i) An ability to use current techniques, skills, and tools necessary for computing practice.

  5. (k) An ability to apply design and development principles in the construction of software systems of varying complexity.

The table below describes how each outcome above is incorporated into this course:

ABET a—​k Description


All four assignments challenge your ability to "design, implement, and evaluate" components of an operating system.


All four programming assignments are performed in pairs, helping you "function effectively on teams to accomplish a common goal".


Preparing design documents is an integral part of the two large assignments, providing practice at effective technical communication, part of the ability to "communicate effectively with a range of audiences".


This course requires students to develop in a virtual machine, use Git for collaborative development, and use modern debugging and code editing tools, all preparing you to "use current techniques, skills, and tools necessary for computing practice".


The course assignments increase in complexity as the semester goes on, allowing students to "apply design and development principles in the construction of software systems of varying complexity".

4.3. Outline

I reserve the right to alter this rough outline as needed to the keep the class current, and our completion of the material will depend on the pace that we are able to establish and your understanding of the material.

  1. Processes and the system call interface

  2. Abstracting and multiplexing the CPU

    1. Interrupts.

    2. Context switches.

    3. The thread abstraction.

    4. Synchronization.

      1. Atomicity and concurrency.

      2. Critical sections.

      3. Synchronization primitives: locks, semaphores, and condition variables.

      4. Solving synchronization problems.

    5. Thread scheduling.

  3. Abstracting and multiplexing memory

    1. The address space abstraction.

    2. Virtual addresses.

    3. Efficient address translation.

    4. Segmentation and paging.

    5. Swapping.

    6. Page replacement policies.

  4. Abstracting and multiplexing disks

    1. Basics of disk operation.

    2. The file abstraction.

    3. File system basics.

    4. File system structures.

    5. File system operations.

    6. File system caching.

    7. The Berkeley Fast File Systems (FFS).

    8. Log-structured file systems.

  5. Operating system structure: micro, macro, exo and multikernels.

  6. Performance improvement.

    1. Measurement.

    2. Benchmarking.

    3. Analysis.

    4. Improvement and Amdahl’s Law.

  7. Hardware virtualization.

    1. Intro to virtualization.

    2. Types of virtualization.

    3. Full hardware virtualization.

    4. Binary translation and paravirtualization.

  8. Special topics (time permitting.

4.4. Programming Assignments

The course includes four programming assignments of increasing difficulty. The assignments themselves are hosted on this website. You also use the website to submit your answers and view your grades. The programming portions of the assignment are graded automatically and you may submit them as often as you like, using the autograder output to improve your submission. Questions that are graded by the course staff may be submitted twice, since they must be graded each time. Each question also has a rubric which indicates exactly how each portion of the question was evaluated and points assigned.

All programming assignments are done in pairs. Both students in each pair receive the same grade for each programming assignment. Each programming assignment also has specific collaboration guidelines that you must indicate you have followed each time you submit answers.

A description of each assignment along with due dates are listed below. This year we expect these to be firm and no extensions will be given.

4.4.1. ASST0: Introduction to OS/161

Introduces you to the programming environment you will be working in this semester, including the OS/161 operating system, the sys161 simulator, the GNU debugger (GDB), and the Git revision control system. Consists of code reading questions, a few simple scripting tasks, and a very simple implementation task.

4.4.2. ASST1: Synchronization

Deadline: Monday 2/22/2016 @ 5PM.

Your first real taste of kernel programming. After completing a set of code reading questions, you implement locks, condition variables and reader-writer locks. Next, you use them to solve a few simple toy synchronization problems.

4.4.3. ASST2: System Calls and Process Support

Deadline: Friday 3/11/2016 @ 11:59PM.

The first big and complex assignment. Start by completing a design that indicates you understand all of the moving pieces and what to do. Next, implement the system call interface. When you are finished, your kernel should be able to run user programs.

4.4.4. ASST3: Virtual Memory

The mountain top. A large amount of code to implement and many internal interfaces to design. As always, start with a careful design. Then implement virtual memory, including address translation, TLB management, page replacement and swapping. When you are finished, your kernel should be able to run forever without running out of memory, and you will have completed the course.

This year we are splitting the ASST3 deadlines into three parts:

  1. ASST3.1: working core map. Deadline: Friday 4/8/2016 @ 5PM.

  2. ASST3.2: user paging. Deadline: Friday 4/22/2016 @ 5PM.

  3. ASST3.3: swapping. Deadline: Friday 5/6/2016 @ 5PM.

4.5. Textbook

There is no required textbook for this course. You can consider Modern Operating Systems to be a supplemental reference for those interested in learning more. The C Programming Language by Kernighan and Ritchie may be a helpful reference when completing the assignments, particularly if you are new to C.

5. Policies

5.1. Grading

Grading is evenly divided between conceptual material and programming assignments.

  • 50% Conceptual

    • 5% Preterm Exam. If you take the preterm exam, you receive 5%. If you do not, your midterm and final exam scores are scaled to fill in the missing 5%.

    • 15% Midterm Exam, 30% Final Exam

  • 50% Programming

5.1.1. Extra credit

This year we will provide up to 5% extra credit to students that help us improve our course materials. All the assignments and lecture slides, as well as other resources including our Vagrant virtual machine configuration and the test161 OS/161 testing tool, are online at our ops-class.org GitHub repository. The amount of extra credit that will be provided will be commensurate with your contribution and completely at the discretion of the course staff.

To take advantage of this offer you must also present your updates to the course staff in a way that makes them straightforward to incorporate. Do not email us, or post in the forum. Clone our repository, fix the problem, and send us a pull request. If you are curious about how much credit a particular change will earn you, post it as an issue on GitHub first and we’ll discuss.

5.2. Incomplete Grades

Please refer to the undergraduate or graduate incomplete policy as appropriate. Of particular importance is this language from the undergraduate incomplete policy (the graduate language is similar):

Students may only be given an I grade if they have a passing average in coursework that has been completed and have well-defined parameters to complete the course requirements that could result in a grade better than the default grade. An I grade may not be assigned to a student who did not attend the course.

Note that for graduate students, "the default grade accompanying an interim grade of I shall be U and will be displayed on the UB record as IU."

5.3. Academic Integrity

Please review the CSE Department academic integrity policy and the UB undergraduate or graduate academic integrity policy as appropriate to familiarize yourself with the relevant academic integrity policies and procedures. In general, the rule of thumb is that talking about code in English is OK, but talking in or exchanging code is cheating. Each assignment has specific guidelines about what types of collaboration are encouraged, discouraged, and forbidden. We will use automated plagiarism detection software to check every submission against solutions submitted in prior years as well as all publicly-available solutions online.

Students that submit plagiarized work will receive a grade of F for the course.

5.4. Disabilities

Please register and coordinate with the Office of Disability Services. Let the course staff know when accommodations need to be made. We are committed to helping you learn.

6. Getting Help

The operating systems programming assignments are difficult and most students require a fair amount of help during the semester. Here’s how to—​and how not to—​get help.

6.1. Great Ways to Get Help

  • Use the the forum. This is by far your best resource because it allows you to get help from anyone—​not just a TA or Ninja—​at any time—​not just during office hours. Please use and contribute to this valuable shared resource.

  • Come to office hours. We don’t hold them for our health and the staff gets bored when there isn’t anyone to help! So please don’t hesitate to come in. Office hours are also a great time to work on your assignments, since if (when) you get stuck help is already nearby.

6.2. Bad Ways to Get Help

  • Emailing any staff member using their @buffalo.edu email address. I instruct the staff to ignore these emails and I will as well.

  • Emailing staff@ops-class.org. This address is only for administrative uses, not for getting help on assignments.

  • Emailing prof@ops-class.org. This address is only for highly-sensitive administrative uses, not for getting help on assignments.

7. Online Resources

This website is the source for all information about the class: the syllabus (which you are reading) lecture slides, assignments, previous exams, lecture videos, and other useful information.

7.1. Videos

We try to tape all lectures and recitations. A playlist of the music played before class is also available. Finally, we are experimenting with screencasts which are embedded into the assignments and also available in a playlist.

Previous years have also been recorded:

7.2. Forum

We are using a Discourse forum this semester for all class-related communications. Please update your profile on it and use it for all lecture- and assignment-related Q&A.

Before we got tired of it and it’s strange approach to pedagogy we used Piazza in past years. Unfortunately, there seems to be no way to make the previous forums contents public 2.

7.3. Mailing List

All enrolled students will be added to a mailing list which we will use for course communication. You are responsible for email messages sent to this list. If you are not enrolled and would like to be added to the list, you can sign up here.

8. Videos



Created 2/17/2017
Updated 9/18/2020
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