1. An apparatus for providing improved emulation performance while emulating in software the hardware and operations of a legacy computer system, utilizing an emulation software program running on a host computer system, the host computer system including a host system operating system, a host central processing unit and a host system memory, the emulation software program residing in the host system memory and including: A) separate first and second emulation code each for emulating at least one legacy system instruction of a plurality of legacy system instructions the first and second emulation code both being a part of the emulation software program and stored in separate areas of memory within the host system memory; B) the first emulation code comprising first code for performing emulation of the one legacy system instruction; C) a signal handler which is given control of the software emulation program, by the host operating system during emulation of the one legacy system instruction by the first emulation code in response to a first host system hardware detected exception condition; and enables recovery by returning control to the second emulation code in the software emulation program; D) the second emulation code comprising a first mechanism for taking control from the signal handler and recovering from the exception condition; the second emulation code further comprising both: 1) code for completing emulation of the same one legacy instruction in the same manner as the legacy hardware system; and, 2) code for performing checks not included in the first emulation code, processing of the code for performing checks thereby avoiding occurrence of any further host system hardware detected exception conditions.