Which Option to Choose? Choose both AS/A Level if you are doing Computer Science as a principal subject.Choose AS Level if you are doing Computer Science as a subsidiary subject. AS Level Computer Science Overview:Duration: 2 YearsExams: 2 PapersFirst Year: Paper 1Second Year: Paper 2 A Level Computer Science Overview:Duration: 2 YearsExams: 4 PapersFirst Year: Paper 1 and Paper 2Second Year: Paper 3 and Paper 4 AS Level A Level