0Eh 2 ALV Pointer to ALT (A8B9h/A8F9h for Drive A/B) Allocation Table
== XDPB - Extended Disk Parameter Block (DPBXDPB,CSA,ALT) for Drive A/B ==
00h 2 SPT Records per Track (CPM/Data=36, IBM=32)
02h 1 BSH Block Shift (3) (records per block = 1 SHL N)
29h 23 ALT Block Allocation Table (23x8bit = 184bit) (only 180bit used)
=== Finding the XDPB for a drive ===
The 2 byte pointer at &BE40 points to a list of DPH structures, 1 per drive, listed in order.