Tandy 1000 SL Technical Reference Manual page 580

BIOS Services
HEX
Offset
From Segment
oo4o:oooo
Bit 5: 0
=
No external mono-
chrome video installed
1
=
External monochrome video installed
B6H
1 byte Bit 0:
0
=
Drive C is 5-1/4"
=
Drive C is 3-1/2"
40:C2 1 byte 01
=
ROM drive is
A:
02
=
ROM drive is B:
03
=
ROM drive is C:
1
59.