This study looked at the effects that individual differences in prior knowledge have on student understanding in learning with multimedia in a computer science subject. Students were identified as having either low or high prior knowledge from a series of questions asked in a survey conducted at the Faculty of Computer and Mathematical Sciences at University Technology MARA, Malaysia. The subject domain chosen for this study is a topic taught to undergraduates in the field of Computer Sciences, in the subject of Operating Systems, i.e., Memory Management Concepts. This study utilizes a multimedia application that is shown to a total of 257 students. Early results from the recall and transfer tests indicate that students' individual differences play a vital role in learning outcome. As expected, the low prior knowledge group scored significantly in the recall tests as compared to the transfer test, and the high prior knowledge group performed comparatively better in the transfer test. This suggests that educational designers who wish to foster learning and understanding should incorporate learners' prior knowledge as a design principle.