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     The bdos function invokes the DOS system call specified by
     <dosfunc> after placing the values specified by <dosdx> and
     <dosal> in the DX and AL registers, respectively. The bdos
     function executes an INT 21H instruction to invoke the system
     call. When the system call is complete, bdos returns the contents
     of the AX register.
 
     The bdos function is intended to be used to invoke DOS system
     calls that either take no arguments or take only arguments in the
     DX (DH, DL) and/or AL registers.
 
     Do not use the bdos function to call interrupts that modify the DS
     register. Instead, use the intdosx or int86x function. The intdosx
     and int86x functions load the DS and ES registers from the
     <segregs> parameter and store these registers in <segregs> after
     the function call.
 
     This call should not be used to invoke system calls that indicate
     errors by setting the carry flag. Since C programs do not have
     access to this flag, the status of the return value cannot be
     determined. The intdos function should be used in these cases.
 
     Return Value
 
     The bdos function returns the value of the AX register after the
     system call has completed.
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