System for delivering exception raised in first architecture to operating system coded in second architecture in dual architecture CPU

A computer concurrently executes a first operating system coded in a RISC instruction set and a second operating system coded in a CISC instruction set. When an exception is raised while executing a program coded in the RISC instruction set, an execution thread may be initiated under the CISC operating system. The exception may be delivered to the initiated thread for handling by the CISC operating system.