; Read a sector using Int13.02 or Int13.42
                ;
                ; INP:  dx:ax = sector number within partition
                ;       bx => buffer
                ;       (_LBA) ds = ss
                ; OUT:  If unable to read,
                ;        ! jumps to error instead of returning
                ;       If sector has been read,
                ;        dx:ax = next sector number (has been incremented)
                ;        bx => next buffer (bx = es+word[para_per_sector])
                ;        es = input bx
                ; CHG:  -
read_sector:


                ; INP:  dx:ax = cluster - 2 (0-based cluster)
                ; OUT:  cx:bx = input dx:ax
                ;       dx:ax = first sector of that cluster
                ; CHG:  -
clust_to_first_sector: