The ESA/390 Architecture is specified by the following documents:
Only the features of ESA/390 processor instruction set and the following optional instructions may be assumed to be present:
additional floating point facility
compare and move extended facility
immediate and relative instruction facility
string instruction facility
Applications conforming to this specification must provide feedback to the user if a feature that is required for correct execution of the application is not present. Applications conforming to this specification should attempt to execute in a diminished capacity if a required instruction set feature is not present.
This specfication does not provide any performance guarantees of a conforming system. A system conforming to this specification may be implemented in either hardware or software.