Ment of such an algorithm is that it minimize the number of random disk seeks during sorting – sequential disk reads are far faster than seeks as we explained in Section 4.1. One solution is the blocked sort-based indexing algorithm or BSBI in Figure 4.2. BSBI (i) segments the collection into parts of equal size, (ii) sorts the termID–docID pairs of each part in memory, (iii) stores intermediate sorted results on disk, and (iv) merges all intermediate results into the final index