Stuck on three:
24a A knot made between two ropes by forming a bight in one and passing the end of the other through the bight, around it and under itself (5,4) S?E?T,?E??
21d A computer programme that facilitates the deletion or insertion of data within information already stored in a computer (6) ???T?R
8d Collections of information, usually in tabular form, for computer processing (4,4) D?T?,S?T?