IBM AT 5170 Technical Reference page 82

The following figure shows the BIOS fixed disk parameters for
fixed disk drive types 16 through 22.
Note: Types 23 through 255 are reserved.
Write
Landing
Type
Cylinders
Heads Pre-Comp Zone
16 612 4
All Cyl
663
17
977
5
300
977
18
977 7 None
977
19
1024
7 512 1023
20
733 5
300 732
21
733
7 300
732
22
733 7
300
733
23
Reserved
255
Reserved
BIOS Fixed Disk Parameters (Extended)
Hex addresses IB through 2D are reserved.
Checkswn (Hex 2E
and
2F)
Bit 7-Bit 0 Address hex 2E-High byte of checksum
Bit 7-Bit 0 Address hex 2F-Low byte of checksum
Note: Checksum is calculated on addresses hex 10-2D.
1-66 System Board