PMIx offers limited backward compatibility with the PMI-1 and PMI-2 definitions. Support for those definitions is provided by translating the called function into its PMIx equivalent – e.g., a call to PMI_Get invokes a wrapper that translates the provided input parameters, calls PMIx_Get, translates the returned PMIx values into a form compatible with the PMI-1 definition, and returns them.

The following table shows the supported and unsupported functions for both sets of definitions. An ‘X’ indicates that the function is supported, while a ‘-‘ indicates it is not supported.

Notes:

• This support is not intended to fully encompass the PMI-1 and PMI-2 definitions. Instead, the intent was to provide a minimum level of support consistent both with that typically required by parallel programming libraries and found in supporting resource managers. Thus, while every PMI-1 or PMI-2 function definition is present in the respective PMIx-provided library, not every function is actually supported. Unsupported functions will return the PMI_FAIL or PMI2_FAIL response.
• PMIx support for a backward compatible definition does not imply support by the underlying host environment – it only indicates that PMIx will communicate the request
• System-provided values (e.g., universe size) may differ from those returned by PMI-1 or PMI-2 due to differences in definitions and/or implementations
• The table rows reflect the API ordering in the original include files

PMIx Backward Compatibility Support
PMI-1		PMI-2
PMI_Init	X	PMI2_Init	X
PMI_Initialized	X	PMI2_Initialized	X
PMI_Finalize	X	PMI2_Finalize	X
PMI_Abort	X	PMI2_Abort	X
PMI_KVS_Put	X	PMI2_Job_Spawn	X
PMI_KVS_Commit	X	PMI2_Job_GetId	X
PMI_KVS_Get	X	PMI2_Job_GetRank	X
PMI_Barrier	X	PMI2_Info_GetSize	X
PMI_Get_size	X	PMI2_Job_Connect	X
PMI_Get_rank	X	PMI2_Job_Disconnect	X
PMI_Get_universe_size	X	PMI2_KVS_Put	X
PMI_Get_appnum	X	PMI2_KVS_Fence	X
PMI_Publish_name	X	PMI2_KVS_Get	X
PMI_Unpublish_name	X	PMI2_Info_GetNodeAttr	X
PMI_Lookup_name	X	PMI2_Info_GetNodeAttrIntArray	–
PMI_Get_id	X	PMI2_Info_PutNodeAttr	X
PMI_Get_kvs_domain_id	X	PMI2_Info_GetJobAttr	X
PMI_Get_id_length_max	X	PMI2_Info_GetJobAttrIntArray	–
PMI_Get_clique_size	X	PMI2_Nameserv_publish	X
PMI_Get_clique_ranks	X	PMI2_Nameserv_lookup	X
PMI_KVS_Get_my_name	X	PMI2_Nameserv_unpublish	X
PMI_KVS_Get_name_length_max	X
PMI_KVS_Get_key_length_max	X
PMI_KVS_Get_value_length_max	X
PMI_KVS_Create	–
PMI_KVS_Destroy	–
PMI_KVS_Iter_first	–
PMI_KVS_Iter_next	–
PMI_Spawn_multiple	X
PMI_Parse_option	–
PMI_Args_to_keyval	–
PMI_Free_keyvals	–
PMI_Get_options	–