As indicated by the name "Stored Program", the SP-1 introduced computer control to the telephone switching market.
With its use of computer hardware and software control, the SP-1 marked an evolutionary step in telephony design.
The voice signal remained in the analog domain throughout the exchange, with the crossbar switches providing a metallic path to connect the end points of a call together.
However the SP1 replaced the previous generation's complex relay-based controllers (markers) with a modern Harvard architecture electronic computer, with separate data and program memories.
The next generation of systems evolved from the SP1 design to replace the analog switch with a digital technology.