INT 21H (0x21)
Function 32H (0x32 or 50) --> Reserved
INT 21H (0x21)
Function 33H (0x33 or 51) --> Get or set break flag,
get boot Drive
Call with: If getting break flag
AH = 33H
AL = 00H
If setting break flag
AH = 33H
AL = 01H
DL = 00H if turning break flag OFF
01H if turning break flag ON
If getting boot drive
AH = 33H
AL = 05H
Returns: If called with AL = 00H or 01H
DL = 00H break flag is OFF
01H break flag is ON
If called with AL = 05H
DL = boot drive (1 = A, 2 = B, etc.)
Comments:
This function obtains or changes the status of the operating system’s break flag, which influences Ctrl-C checking during function calls.
INT 21H (0x21)
Function 34H (0x34 or 52) --> Reserved
INT 21H (0x21)
Function 35H (0x35 or 53) --> Get interrupt vector
Call with: AH = 35H
AL = interrupt number
Returns: ES: BX = segment: offset of interrupt handler
Comments:
This function obtains the address of the current interrupt-handler routine for the specified machine interrupt.
INT 21H (0x21)
Function 36H (0x36 or 54) --> Get drive allocation Information
Call with: AH = 36H
DL = drive code (0 default, 1 = A, etc.)
Returns: If function successful
AX = sector per cluster
BX = number of available cluster
CX = bytes per sector
DX = cluster per drive
If function unsuccessful (drive invalid)
AX = FFFFH
Comments:
This function obtains selected information about a disk drive.
This function is very important in data recovery and disk troubleshooting programming from which the drive’s capacity and remaining free space and many other important things can be calculated.
INT 21H (0x21)
Function 37H (0x37 or 55) --> Reserved
INT 21H (0x21)
Function 38H (0x38 or 56) --> Get or set country information
Call with: If getting country information
AH = 38H
AL = 0, to get current country information
1-FEH, to get information for
countries with code <255
FFH, to get information for countries
with code >=255
BX = country code, if AL = FFH
DS:DX = segment: offset of buffer for returned
information
If setting current country code
AH = 38H
AL = 1-FEH, country code for countries
with code <255
FFH, for countries with code >=255
BX = country code, if AL = 0FFH
DX = FFFFH
Returns:
If function is successful
Carry flag = clear
And, if getting internationalization information
BX = country code
DS: DX = segment: offset of buffer holding
internationalization Information.
If function is unsuccessful
Carry flag = set
AX = error code
Comments:
This function obtains international information for the current or specified country or sets the current country code.
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