IBM Personal System/2 50 Technical Reference page 49

Bits 7 - 4
Bits
7654
0000
0001
0011
0100
These bits indicate the first diskette drive type, as shown
in the following figure.
Function
No drive present
Double-sided diskette drive (48 tracks per inch, 360KB)
High-capacity diskette drive (720KB)
High-density diskette drive (1.44MB)
Note: All combinations that are not shown are reserved.
Figure 3-18. Diskette Drive Type Byte (Bits 7 - 4)
Bits 3 - 0
Bits
3210
0000
0001
0011
0100
These bits indicate the second diskette drive type, as
shown in the following figure.
Function
No drive present
Double-sided diskette drive (48 tracks per inch, 360KB)
High-capacity diskette drive (720KB)
High-density diskette drive (1.44MB)
Note: All combinations that are not shown are reserved.
Figure 3-19. Diskette Drive Type Byte (Bits 3 - 0)
First Fixed Disk Drive Type Byte (Hex 011): This byte defines the type
of the first fixed disk drive (drive C). Hex 00 indicates that a fixed disk
drive is not installed.
Second Fixed Disk Drive Type Byte (Hex 012): This byte defines the
type of the second fixed disk drive (drive D). Hex 00 indicates that a
fixed disk drive is not installed.
Note: For more information about fixed disk drive types, refer to the
IBM Personal Systeml2 and Personal Computer BIOS Interface
Technical Reference.
Reserved Byte (Hex 013): This byte is reserved.
Model 50 System Board 3-21