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Computer Science 61 and E61
Systems Programming and Machine Organization
This is the 2012 version of the course. Main site


This page contains information specific to Extension School students.


Prerequisites for this course for Extension School students are CSCI E-52, CSCI E-113, or experience programming in C.

Note: This course requires programming in C. You should deeply understand C pointers and arrays before taking this course. Ideally you should already have experience programming in C. If you have not previously programmed in C but know another procedural language, such as Java, you will likely be able to quickly learn what you need. See the resources page for pointers to material for learning C. Talk to the instructor if you are unsure whether you are sufficiently prepared for CS 61.

Add/Drop deadlines

Please see the Extension School calendar for details of registration dates, add/drop dates, etc. Note that the withdrawal deadlines are September 11, September 18, and November 30.


Extension School students are welcome to physically attend lectures and the Extension School section. If you would like to attend one of the other sections (either on a regular basis, or occasionally) please contact the course staff.

Lecture and Section videos

The live video stream is available only during class hours. You can access the stream here.

Recorded (not live) videos will typically be available a day or two following the lecture. You can access the video archive here.

Office Hours

Office hours for Extension School students will be held over Skype. There will be scheduled office hours, which will be posted here soon. Additionally, students can make arrangements to meet on Skype. The CS61 staff Skype username is "cs61tf" (lowercase) with open-hour support. You are all encouraged to make use of this - it's especially useful for quick questions you may have, and don't want to hold until office hours

Course staff and sections

Course staff information

Jonathan Levin is the TF especially for Extension School students. However, all students, including extension school students, should use Piazza (or, alternately, cs61-staff@seas.harvard.edu) for requests.


The first section will take place Thursday, September 20th, 17:00. This will be a conf call over Skype. The username to contact is cs61tf. Those doing so will be placed into conference, and the fun can begin!


Extension School students sit the same exams as College students: one midterm exam, and a final exam.

The midterm exam will be held on Thursday October 18. It is an 80 minute exam. For those not attending the exam, you must sit it within a 36 hour window (noon on October 17 to midnight on October 18).

The final exam will be held on Friday December 21, at 2pm. It is a 3 hour exam. For those not attending the exam, you must sit it within a 36 hour window (noon on Thu Dec 20 to midnight on Fri Dec 21).

Please refer to the Extension School pages on exams for information on requirements for Extension School students taking exams.