Appendix
C
I
MS-DOS Memory Map
The equipment check BIOS call (INT 11H) and memory size
BIOS call (INT 12H) return information from the following data
areas:
HEX
Offset From
Length and
Segment
0040000
Intended Use
10H Devices installed word
13H Memory installed word
The structure and usage
of
the
area is
as
follows:
HEX
Offset From
Segment
00400000
3EH
1
byte
-
3FH
1
byte
-
40H
1
byte
-
41H
1
byte
-
42H
Value
OIH
02H
03H
04H
08H
09H
10H
20H
40H
80H
floppy disk driver RAM data
Length and
Intended Use
drive recalibration status
-
bit
3-0, if 0 then drive 3-0 needs
recal before next seek bit
7
indicates interrupt occurrence
motor status
-
bit 3-0 drive
3-
0 motor is
ordoff,
bit
7
-
current operation is write,
requires delay
motor turn
off
time out
counter (see Timer ISR)
disk status
-
codes defined
below
7
bytes
-
7
bytes
of
status returned by
the controller during result phase
of
operation
Error
Condition
Illegal Function
Address Mark Not Found
Write Protect Error
Sector Not Found
DMA Overrun
Attempt
to
DMA
Across
a
64K Boundary
Bad CRC on Disk Read
Controller Failure
Seek Failure
Device Timeout, Device Failed
to
Respond
231
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