This paper presents the results of a study on the effects of using 3 simulators with 14 computer science majors enrolled in an undergraduate computer architecture course. Three ability groups (high, medium, and low) were formed based on the students' quality point averages for prior computer science courses. Analyses of data from a pretest, a posttest, instructor-prepared achievement tests following each of the simulators, programming assignments, and survey results showed: (1) no significant differences among the three groups on the pretest and posttest scores; (2) only the low and medium ability groups showed significant performance gains from pretest to posttest; (3) the use of the simulators equalized the student performance in the three ability groups; (4) nonsignificant differences on both programming assignments for all ability groups; (5) positive student attitudes toward and perceptions of the use of simulators; and (6) student perceptions that the simulators made learning about computer architecture more concrete, and helped in writing and understanding programs and microsequences of instructions. Suggestions for further research are presented including using larger samples, different methodology for defining the ability groups, and the use of qualitative interviews to ascertain student perceptions. Six figures present the results of the various statistical analyses. (Contains 5 references.) (ALF)