CS 256 - Computer Organization and Architecture - Spring 2019


Die shot of a quad-core CPU
This is a microprocessor. We're going to learn how this thing, along with the rest of the computer, runs your code.

If we have a reasonable understanding of what computers can do, a logical next step is to think about how they can do it. If I write var = var + 1; in C, what does the computer actually do, "behind the scenes," to make that happen? What are all of those parts inside the computer, and how do they work together? And how are they designed to be as efficient as possible?

We will approach these questions from two different directions. Computer science contains an abundance of abstraction, and this course investigates several layers of abstraction below what you have likely previously studied. In one direction, primarily in lab, we'll start from a very low level, the physical building blocks of digital electronics, and work upwards, building more and more complex structures as we reach towards a complete computer. In the other direction, we'll work from what we know of high-level programming languages down towards the physical implementation of a machine that can execute such code. In the middle, the two directions will often meet, joining to form a complete connection from code to electrons.

For an idea of the specific topics covered in the course, see the rough schedule for the semester.


Lecture: TR 2:35-3:50PM / CNS E201
Lab: Tuesday 7-9PM / CNS E203
Instructor: Mark Liffiton
Office: CNS C207B   (2nd floor CNS, in middle of building over atrium
Office Hours: (visual schedule)
Mon, Tue, Wed, Thu 10-11am; Tue 4-5pm; or email/drop in any time.
If your schedule prevents you from attending my office hours, I'm happy to set up alternate meetings.
Contact (you→me): Email is preferred (please start the subject with "CS256:").
For more pressing matters, my office # is 309-556-3535.
Contact (me→you): I will post course announcements through Moodle, and they will be sent to your IWU email accounts. Check your IWU email frequently or have it forwarded to an address you do check.
TA: Duc Tran
TA Hours: Mon 7-9pm, Wed 7-10pm in CNS E201
Email: dtran1@iwu...
Textbook: Computer Organization and Design: The Hardware/Software Interface
Authors: David A. Patterson and John L. Hennessy
ISBN: 9780124077263 (5th ed.)
Note: The 4th edition has mostly the same content, as long as you are okay figuring out the mapping of sections and page numbers between editions.
Note: Be sure you get the MIPS version, not the ARM version. Students have ended up with the wrong version when ordering the international edition in the past, and it does matter.

Other Pages

Semester schedule — tentative - see the Moodle for up-to-date details.

Moodle — reading, assignments, quizzes, announcements, and other online resources will be posted here.

Online Resources — notes, readings, and other resources will be posted here. I will link to relevant entries from the Moodle page, but it doesn't hurt to browse and see what else is there.


The final grade will be based roughly on the following breakdown:

Exam 120%
Exam 220%


* You can create PDFs from any document in OS X (instructions) or Windows 10 (instructions) or previous versions of Windows using a free tool like DoPDF.
LibreOffice, Google Docs, and many other word-processing applications can produce PDFs directly, as well.

Assignments will be posted on the course's Moodle site, usually about a week before they are due, and they will be collected there as well. Submissions should be in the form of plain text or PDF*. I will aim to get them graded and returned to you by the following week.

Your lowest assignment score will be dropped.


The labs will be hands-on explorations of hardware concepts, generally involving designing, building, and testing digital logic circuits.

Lab assignments will be posted on the course's Moodle site. Reports should be submitted on the Moodle as PDF files. The desired format of the reports will be specified on the Moodle. I will aim to get them graded and returned to you by the following week.

Late Policy

Assignments and Labs will be due at set times; they will be considered late at any point after that time. An assignment will lose 10% of the total possible points for every day it is late, and after five days it will not be accepted.

Assignments can't be accepted at all after solutions have been handed out or the graded work has been returned to the class.


There will be two exams during the semester, held in class.


As you may have heard from other teachers: If everyone does well, that's great! I'm not going to lower anyone's grade to fit some predetermined grade distribution. However, scores given on individual quizzes or exams (especially exams) may not translate directly into a letter grade on the traditional scale. As explained quite well here:

"A percentage shows how much of a particular exam was dealt with successfully, but what test is so perfect that it could completely determine extent of knowledge or ability? If a student gets a grade of 90%, it does not mean they know 90% of everything in the subject. Wise students will begin to look at scores as a place on a continuum of achievement rather than analysis carved in stone."


If you would like to request a regrade, submit a request in writing (via email) within one week of receiving the graded assignment, exam, etc. Indicate exactly which part you believe deserves a different score and why.

Engagement / Attendance

Class time will be complementary to the reading, and you will need both in order to learn all of the material in this class. Furthermore, each student benefits from the engagement of all others in the class. Ten percent of your final grade will be based on that engagement. Attending every class period on time and prepared is the minimal expectation, worth about 70% of the engagement points. Points can be gained by constructive participation, in class or out, such as asking questions, answering them, responding in the forum, sharing insights or useful/interesting resources with the class (posting in the forum, for example), investigating concepts beyond the requirement in class, working on small independent learning projects, and in many other ways; points can be lost for excessive (more than 3) unexcused absences, disrupting class (e.g., regularly showing up late), dominating the conversation, and the like.

Absences can be excused with documentation from health services or the Dean of Students' office, or if arrangements are made with me more than a week in advance. In general, if you know you will be missing a class, let me know as soon as you do.

Office Hours

If any concept, piece of code, compiler error, or anything else related to this course is ever unclear to you, please come see me during my office hours. One-on-one, I can help you bridge the gap from what you do understand to what you want to understand. It will generally be the easiest, fastest way to clarify something.

If you cannot attend any of my regularly scheduled office hours, I'm more than happy to setup another time to meet. Just let me know.

And to make sure that misunderstandings and difficulties do not go unaddressed, I will ask that anyone who receives a C- or below on any assignment or exam come see me to see what we can do about improving that going forward.

Working with Others

I strongly encourage you to form study groups with your classmates, compare notes, explain concepts to one another, and generally help each other learn the material in this course.

Any material turned in for a grade must be your own individual work, though. You may work on concepts with other students, but I ask that you not discuss assigned problems until after the work has been turned in. Giving or even showing your solutions or code to another student is not allowed.

This has two goals: 1) let the grades be a reflection of each student's own work, and 2) avoid situations where one person solves a problem and another records the answer as their own work without really learning. I understand that the line between discussing concepts and solving problems can be vague, so I ask that you use your own judgement with those two goals in mind and ask me if a situation is unclear.

For details on the university's policies regarding academic honesty, please read the sections of the student handbook on conduct, cheating, and plagiarism here. Cheating of any form can result in failing the course and a report to the associate provost.


Illinois Wesleyan University strives to make all learning experiences as accessible as possible. If you anticipate or experience academic barriers based on a disability (including mental health and chronic or temporary medical conditions), it is your responsibility to register with Disability Services. Please note that accommodations are not retroactive and accommodations cannot be provided until I receive an email from Disability Services. Once the email is sent, please make arrangements with me as soon as possible to discuss your accommodations confidentially so they may be implemented in a timely fashion. For more information contact Disability Services by visiting 110 Holmes Hall, calling 309-556-3231, or emailing cshipley@iwu.edu.


Our university's mission statement includes, "The University through our policies, programs and practices is committed to diversity [...]" Our school and this course are made stronger by the mix of people that come into it bringing a diversity of ideas, experiences, and backgrounds. I expect everyone in this course — instructor, TA, and student — to contribute to an inclusive atmosphere that respects the diversity of all others in it. Dimensions of diversity can include sex, race, age, national origin, ethnicity, gender identity and expression, intellectual and physical ability, sexual orientation, income, faith and non-faith perspectives, socio-economic class, political ideology, education, primary language, family status, military experience, cognitive style, and communication style. The individual intersection of these experiences and characteristics must be valued in our community.
[adapted from UCF FCTL]

End-of-Syllabus Advice

Help each other. This is good advice for any course. By working out concepts with others or teaching someone about something you've already worked out yourself, you can greatly improve your understanding. Teaching or any other kind of back and forth will point out any gaps in your understanding, trust me; as a student, I learned a great deal and did well in many classes primariliy because I helped others. In this course, helping each other is perhaps even more useful than normal, because the course is full of new kinds of ideas. Much of it will not be programming, will not be math, and will not be like anything you've done before. With everyone starting from a similar baseline, each person in the class might have a valuable insight or perspective on a particular concept that can be shared with the rest. The lab will also be very conducive to this sort of sharing; if you come up with a helpful way of working or thinking in the lab, let the rest of us know! There is no competition here.