Many on-campus job fair, but the email piles are too high, if you're not brilliant enough, may not have chance to be remembered. Top student from top schools may have better chance. It is efficient through internal employee referral, a IBMers are normally believe each other, and believe if an internal IBMer sent a resume, this IBMer should have the responsibility and ethic to screen out if this candidate will be a good fit.
After nail down a good resume showing good courses learned, good project done, relevant experience/exposure to the current role, a phone interview from HR related hiring manager will be conducted, normally this is easy one, this hiring manager will ask more of resume related questions, focusing on the technical skills that may be relevant to this role. So understand the job description and make a connect of your background is always helpful.
If the 1st interview is good, if candidate is remote, another 2~3 phone interviews will be conducted by the senior technical lead who'll directly interact with this candidate. This will be very hard core interviews. Normally IBMers don't want to show their smartness and ask brutal questions to see how you suffer. All they care is to make sure you do have sufficient technical skills, experience to assume the job and whether you have the potential to do better. So no matter what, just be yourself, if your technical skill doesn't match, there is not much value to spit the hair, but if you feel it is something you can do and will be fun for you, do some research, there are tons of available online information about IBM products/services, learn from there.
If 1st interview is good, and if candidate lives around, maybe an onsite interview will be done, very similar to the questions mentioned above. People also have a chance to see you as a person, whether you're very agreeable, nice and have can-do attitude. Dress formal, at least semi formal. It still has somewhat traditional blue culture.