<p>HCI = Human computer interaction, which is a subfield of Computer Science (CS). </p>
<p>The two majors are fairly different. You can only do HCI as a 2nd major while CS is available as both a primary and secondary major. In addition, you have to submit an application to study HCI but don’t have to apply to study CS. Check the CMU course-catalog for information on the coursework for both majors.</p>