Transformer Read Only Storage

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Transformer Read Only Storage (TROS) was a type of ROM used in the 1960s and early 1970s before solid state memory devices were developed.


Transformer matrix ROM (TROS), from the IBM System 360/40

The idea of TROS was to create a Read Only Storage method to contain computer microcode. There were several implementation methods used but one notable method used the same technology as core memory that was the primary method of computer memory used during the same period. The specific method was called Core rope memory which used a ferrite core with wires strung through the core like a standard core memory but in some cores one of the wires would be routed around the core itself. The routing of this wire determined the interpretation of a 1 or a 0 with 1 representing a wire that ran through the core and a zero representing a wire that looped around the core.


TROS memory was used as microcode in mainframe computers and also as microcode in intelligent controllers used to control sophisticated memory devices such as disk drives and tape drives. If there were a bug in the microcode it was possible to rework the memory by carefully rerouting the wire and thereby change the contents of memory.