Because we do not know how large the postings list of a term will be when we first encounter it, we allocate space for a short postings list initially and double the space each time it is full (lines 8–9). This means that some mem- ory is wasted, which counteracts the memory savings from the omission of termIDs in intermediate data structures. However, the overall memory re- quirements for the dynamically constructed index of a block in SPIMI are still lower than in BSBI.