Which Shimano system is often credited with popularizing reliable indexed shifting by matching all drivetrain parts?

Answer

SIS (Shimano Index System)

Shimano's SIS system was revolutionary because it engineered the shifter, derailleur geometry, and cable pull ratios to work together perfectly, ensuring reliable indexing across all gears.

Which Shimano system is often credited with popularizing reliable indexed shifting by matching all drivetrain parts?
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