SIMMON

SIMMON (SIMulation MONitor) was a proprietary software testing system developed in the late 1960s in the IBM Product Test Laboratory, then at Poughkeepsie, N.Y. It was designed for the then-new line of System/360 computers as a vehicle for testing the software that IBM was developing for that architecture. SIMMON was first described at the IBM SimSymp 1968 symposium, held at Rye, New York.

SIMMON was a hypervisor, similar to the IBM CP-40 system that was being independently developed at the Cambridge Scientific Center at about that same time. The chief difference from CP-40 was that SIMMON supported a single virtual machine for testing of a single guest program running there. CP-40 supported many virtual machines for time-sharing production work. CP-40 evolved by many stages into the present VM/CMS operating system. SIMMON was a useful test vehicle for many years.

SIMMON was designed to dynamically include independently developed programs (test tools) for testing the target guest program. The SIMMON kernel maintained control over the hardware (and the guest) and coordinated invocation of the test tools.

Two modes of operation were provided:

In this mode, each instruction in the guest program was simulated without ever passing control directly to the guest. As an Instruction Set Simulator, SIMMON was unusual in that it simulated the same architecture as that on which it was running, i.e. that of the IBM System/360/370. While an order of magnitude slower than Interrupt mode (below), it allowed close attention to the operation of the guest. This would be the mode used by various instruction trace test tools.

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