GECO

GECO is a customer-specifed instruction which appears to be included as part of the standard instruction set from ND-100/CE and later. The name comes from the customer, GECO (Geophysical Company of Norway).

SINTRAN III version L, and probably version K and possibly earlier, tests for GECO as part of the startup. From this it looks like the registers B, D, A, and X are all used as input parameters. When all are set to 0 the instruction seems to do nothing.