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INT 0x21 - 0x3f - Read From File or Device Using Handle


reg value descr
AH 0x3f
BX file handle
CX number of bytes to read
DS:DX pointer to read buffer


CF is cleared : success

reg descr
AX number of bytes readed

CF is set: error

reg descr
AX error code (see DOS Error Code)

Notes & Comments

  • read specified number of bytes from file into buffer DS:DX
  • when AX is not equal to CX then a partial read occurred due to end of file
  • if AX is zero, no data was read, and EOF occurred before read


back2root/ibm-pc-ms-dos/interrupts/int_21/int_21_3f.txt · Dernière modification : 2023/01/16 17:54 de