IBM 560 - Manual (Page 46)

Hard Disk Drive Type Byte (Hex 012): This byte defines the type
of hard disk drive installed. Hex 00 indicates that no hard disk drive
is installed.
Figure 2-26. Hard Disk Drive Type Byte
Bit Drive Type
7–4 Hard disk drive 0
3–0 Hard disk drive 1
Reserved Bytes (Hex 013): These bytes are reserved.
Equipment Byte (Hex 014): This byte defines the basic equipment
in the system for the power-on diagnostic tests.
Figure 2-27. Equipment Byte
Bit Description
7, 6 Number of diskette drives
5, 4 Display operating mode
3, 2 Reserved
1 Coprocessor presence
0 Diskette drive 0 presence
Bits 7, 6 These bits indicate the number of installed diskette
drives.
Figure 2-28. Installed Diskette Drive Bits
Bits 7,6 Number of Diskette Drives
0 0 One drive
0 1 Reserved
1 0 Reserved
1 1 Reserved
Bits 5, 4 These bits indicate the operating mode of the display
attached to the video port.
Figure 2-29. Display Operating Mode Bits
Bits 5,4 Display Operating Mode
0 0 Reserved
0 1 40-column mode
1 0 80-column mode
1 1 Monochrome mode
2-24 ThinkPad 560/560E System Board