Abstract The study examined the codes peculiar to the sub-registers of Computer Science for learners’ communicative competence. The data was collected through a textual analysis of forty Computer Science texts covering eight sub-registers of Computer Science. The researchers used the Systemic Functional Linguistics as a model to examine the alphanumeric codes in the texts. The study reveals that four sub-registers of Computer Science namely; computer architecture, database management system, Programming language and computer security contained more codes than the other sub-texts. It was discovered that the texts contained different codes in the forms of mathematical symbols, illustrative symbols, flowchart symbols, pictures and icons. A significant number of sentences contained both verbal and non-verbal materials. Also, the codes had their verbal interpretations. The researcher also highlighted the functions of the codes as used in the texts. There, these codes are relevant for discipline Specific English (ESP) and for the communicative competence of learners.