Answer by Rahul Biswas:
(on leave from the CS Ph.D. program at Stanford)
copying this answer from my own webpage
Many people write to me asking about admission to the Computer Science department here at Stanford University. I had many of the same questions when I was applying and others were kind enough to answer my questions. It's not possible for me to answer individual questions by e-mail but if you have a question and e-mail me, I am happy to post the answer here so that everyone can benefit. This page does not constitute official policy but the reflections of one student who is no longer involved in making admissions decisions. I believe that my answers apply beyond Stanford but there is a sharp drop-off in what admission committees expect after the top 10 schools so plan accordingly.
Q. How are admissions decisions made?
A. For the M.S. program, typically two professors and/or current M.S. students will individually review your application and assign you a numeric score. How they do that is up to them and scores are informally normalized. If your application is especially weak, you may be rejected without review. If both reviewers feel that your application is weak, you will not receive further consideration. If, on the other hand, both reviewers find that you are highly qualified, you will be admitted without further review. Most admits fall into neither of these categories and are discussed by a committee of several professors.
Thus you should be careful to distinguish between the administrative staff who will prepare your file and the reviewers who will actually read it. Your application will be reviewed quickly so take care to be clear and concise. Submit all necessary documents in a timely fashion. I suggest including self-addressed, stamped postcards with everything you submit so that you can know that your documents were received by the receipt of your own postcard. The admissions committee will never see such things and an incomplete file is the quickest path to rejection. It is your responsibility to make sure your file is complete.
Q. What kind of GRE scores do I need to be admitted?
A. Your GRE scores will not substantially influence your chances for admission unless you do poorly on them. A Math score of 750 or higher is adequate and an 800 is best. More leeway is given for the English and Writing sections. A score of 600 or above (and something comparable on the Writing) is needed and 700 is considered good. Higher scores will attest to your writing ability and are especially helpful if you are applying from abroad. If your application is otherwise strong, you will not be disqualified on the basis of GRE scores alone.
I suggest you spend considerable time and effort preparing for the GRE until you are confident you can get the 800 / 700 as mentioned above. You're probably applying to several graduate programs and the GRE is consistently considered important in most programs. You will benefit substantially for relatively little effort.
Q. Whom should I ask for letters of recommendations? What should they discuss?
There are two important factors to consider when asking for letters of recommendation or undertaking research and/or work opportunities that will lead to opportunities to ask in the future. The first factor is the importance of the person writing the letter for you. It is helpful if this person has a Ph.D. from a reputable university. The more reputable the better but any top 50 university is usually adequate. The second factor is how much the person likes you. At least one letter should be from someone who has supervised you in a professional capacity and things highly of you. Thus when asking, you should seek a balance between these two factors. Typical admits will have one letter from a professor at their undergraduate institute who has supervised them in undergraduate research. Another letter may be from another professor who has supervised research or an especially successful class project. A third may be from a manager at an internship. It is best if the first is especially strong. Any subsequent letters will probably be discarded and since you don't know which one will be thought of as an extra one, don't send them. The third letter can be ambivalent and it will not harm your chances for admission by very much.
Letters of recommendation are very important for M.S. admission and the deciding factor for Ph.D. admission. It is well worth your time working hard for those whom you plan to ask for letters. If someone is qualified to write the letter, they will know what to write and will probably not ask you to write the letter yourself. If you do have to offer guidance or write your own though, write about projects that you worked on and how you demonstrated competence and intelligence in your undertaking.
Q. What should I write about in my statement of purpose?
Your statement of purpose serves two equally important purposes. First, it demonstrated whether you write and think clearly. Second, it shows whether you are ready to undertake individual research. You are expected to be more ready if you are applying to the Ph.D. program. Unlike your essay for undergraduate research, you are not expected nor benefited by demonstrating artistic flair in your statement. Write about projects you have worked on in the past, what role you played in those projects, and what you would like to do research on if accepted into the program you are applying for. Be specific but remain open-minded. The rationale behind this is that there may not be anyone who works on the project you are interested in or the person who does work in that area may not be looking for more students. Others may be interested in you though. Specificity, on the other hand, demonstrates maturity and mastery. Don't fret too much about assuming background knowledge. If someone in the department will know what you're talking about, the reader will give you the benefit of the doubt or forward your statement to that person. Do not discuss why you like engineering or computers or how you came to be interested in such topics. You may want to mention a few professors in the department you may be interested in working with if admitted.
Q. What kind of funding is available for students?
A. The answer below applies to both domestic and international students except that if you are an international student, you are generally forbidden from seeking employment outside the university except in the summer as an intern. There are plenty of opportunities to be a teaching assistant (help professor teach courses) or a research assistant (receive remuneration for doing research) as an M.S. student. As a Ph.D. student, you are guaranteed funding. You are not eligible for a teaching assistantship during your first quarter. Finding such opportunities requires some effort but typically, if you're good enough to get in, you're good enough to receive some sort of funding. If you are especially bright, you may apply for and secure external fellowships. Funding is generally not a big problem but it is best if you can stash or borrow enough to pay for expenses during your first quarter while you are getting settled. $1000 / month past housing and tuition costs should ensure that you will not starve. I know some who get by on less.