CS 256 - Computer Organization and Architecture - Spring 2012


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;, 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, often, the two directions will 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.


When/Where: TR 2:35-3:50PM / CNS E201
Lab: Tuesday 7:00-9:00PM / CNS E203

Instructor: Mark Liffiton
Office: CNS C207B   (2nd floor CNS, directly above entrance from quad)
Office Hours: MW 10-11; TR 10-10:45; T 4-6; by appointment F 10-12; or email/drop in any time.
Contact: Email is preferred (please start the subject with "CS256:"). For more pressing matters, my office # is 309-556-3535.

TA: Kate Siebels, ksiebels@iwu...

Textbook: Computer Organization and Design: The Hardware/Software Interface by David A. Patterson and John L. Hennessy
ISBN: 978-0123744937 (4th ed.) or 978-0123747501 ("revised 4th edition") — I suggest the 4th edition, but either is fine.
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.

Online References — mostly provide alternative sources or general reference.

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


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

Exam 115%
Exam 215%
Final Exam20%


* You can create PDFs from any document in OS X (instructions) or in 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 in the assignments. I will aim to get them graded and returned to you by the following week.


There will be two exams during the semester, held in class. The final will be held during the final period, time TBD.


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."

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.


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 points of your final grade will be based on that engagement. Attending every class period on time and prepared will earn a base of 7 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.

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 specifics of the assigned problems until after the work has been turned in. 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.

Try to follow this rule of thumb: No matter what help you received figuring out the concepts involved, when you turn something in you should be able to reproduce the whole thing, working through the assignment again, without any outside help.

For details on the university's policies regarding academic honesty, please read the sections of the student handbook on conduct, cheating, and plagiarism here.

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.