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Computer Science 61 and E61
Systems Programming and Machine Organization


This page contains information specific to Extension School students. Extension students are also subject to the course policies for all students.


Prerequisites for this course for Extension 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 9, September 16, and December 1.


Extension students are welcome to physically attend lectures and sections. We will have a section, which will be recorded, and for which live video will be available, at a time to be determined once class begins. If you would like to attend a different section (either on a regular basis, or occasionally) please contact the course staff.

Lecture and Section videos

Recorded videos will typically be available a day or two following the lecture.

Office Hours

Office hours for Extension School students will be held over Skype. There will be scheduled office hours. Additionally, students can make arrangements to meet on Skype. The CS61 staff Skype username is "cs61staff" (lowercase).


Assignments for Extension students are the same as for College students, and the same policies apply regarding late days, grading, etc.

One exception is that assignments for Extension students are due exactly 24 hours after the College student deadline (i.e. Fridays at midnight). This only applies to assignments, and not forms that we may need you to fill out or exams.

Like other students in the course, Extension students may work in pairs for the assignments that allow this. Extension students may work with other Extension students or with College students, although we find that Extension pairs work best (because Extension students tend to have similar schedules). Please contact the course staff if you would like to work with a partner but are having trouble finding someone.

Course staff and sections

Course staff information

All students, including extension school students, should use Piazza (or, alternately, cs61-staff@seas.harvard.edu) for requests.


Extension students sit the same exams as College students: a midterm exam in mid-October, and a final exam in mid- to late December. Exam dates will be posted on the schedule. We will provide proctors during a several-hour window in the evening for those in the Boston area. For those not attending the exam in person, you must sit for the exam, with a proctor arranged through the Extension School, within a 24 hour window starting on the exam day at the time of the college exam.

Please refer to the Extension School pages on exams for more information on Extension School exam requirements and proctoring.


Extension students are given the same work as College students, but graded on a different curve (College student marks won’t affect Extension student marks, and vice versa).