IBM XT 5160 Technical Reference page 156

If you do DEF SEG (Default workspace segment):
Offset
Length
2E
2
Line number of current line being executed
347
2 Line number of last error
30 2
Offset into segment of start of program text
358
2 Offset into segment of start of variables
6A
(end of program text 1-1)
1
Keyboard buffer contents
O=No characters in buffer
l=Characters in buffer
4E 1 Character color in graphics mode*
.....
Set to 1, 2, or 3 to get-text in colors 1-3.
Do not set to O. The default is 3.
Basic Workspace Variables
Example
100 PRINT PEEK (&H2E)
+
256 x PEEK (&H2F)
L
Hex 64
H
Hex 00
Starting Address
00000
BIOS interrupt vectors
00080
Available interrupt vectors
00400
BIOS data area
00500
User read/write memory
c8000 Disk Adapter
FOOOO
Read only memory
FEOOO
BIOS program area
BIOS Memory Map
BIOS Programming Hints
The BIOS code is invoked through software interrupts. The
programmer should not "hard code" BIOS addresses -into
application programs. The internal workings and absolute
addresses within BIOS are subject to change without notice.
If an error is reported by the disk or diskette code, you should
reset the drive adapter and retry the operation. A specified
number of retries should be required on diskette reads to ensure
the problem is not due to motor startup.
System BIOS 5-9