I am applying for computer science PhD in the US. From answers of @Nathan S. in Is it unwise to contact the professor directly before getting admitted to a program in US? and @aeismail in How to contact professors for PhD vacancies?, I learn about two ways of how admission systems work:
Admissions are granted by the small group to which I am applying, where each professor is a member of the committee. Based on my understanding, contacting professors beforehand with good research questions and a personal background introduction is very helpful in this case.
Admissions are determined by a departmental committee. After admissions, there will be team matches between students and professors. Contacting professors then becomes not so critical in this case.
I fully understand the first case, but I am curious about how the second one works in practice. Many professors, especially those from the top universities, do warn prospective students on their home page to not contact them because decisions are made by the committee. I wonder what differentiates these two because the departmental committee will be made up of professors anyway.
Update: Thanks for the reference from @buffy Do PhD admissions (CS) in the US work on two levels (general decisions and PI decisions)?, the difference largely comes from the funding model.
As the name implies, the committee may consist of some professors but not all. So my questions are: does it mean there will be a group of professors to evaluate the research potential for each prospective student solely based on their academic background? If it is the case, is the best thing I can do is to submit materials and pray?
A follow-up question is: Are there any public sources where I can learn the style of admission systems of the computer science department of each university?
Thanks a lot!