Most Int 31h calls can fail. The DPMI 0.9 specification does not specify error return codes for most calls. When a call fails it will set the carry flag and return with the value in AX unmodified unless otherwise specified. However, future DPMI implementations will return error codes in the AX register. All specific error codes will have the high bit (bit 15) set. If a function returns with carry set and the high bit of AX clear, it should be treated as a general failure. Specific error codes will allow programs running under future DPMI implementations to take appropriate corrective action in some cases.