IBM 5170 Technical Reference page 72

Diskette Drive Type Byte (Hex 10)
Bit 7-Bit 4
Type of first diskette drive installed:
0000
No drive is present.
0001
Double Sided Diskette Drive (48 TPI)
0010
High Capacity Diskette Drive (96 TPI)
Note: 0011 through 1111 are
reserved.
Bit 3-Bit 0 Type of second diskette drive installed:
0000
No drive is present.
0001
Double Sided Diskette Drive (48 TPI)
0010
High Capacity Diskette Drive (96 TPI)
Note: 0011 through 1111 are
reserved.
Hex address 11 contains a reserved byte.
Fixed Disk Type Byte (Hex 12)
Bit 7-Bit 4 Defines the type of first fixed disk drive installed
(drive C):
0000
No fixed disk drive is present.
0001 through 1111 define type 1 through type 15
(see BIOS listing at label FD_TBL).
Bit 3-Bit 0 Defines the type of second fixed disk drive
installed (drive D):
0000 No fixed disk drive is present.
1-50 System Board