The RX100 designation was originally used in certain markets for the five-speed, short-stroke 97cc Yamaha RS100DX produced from 1977. This was an RS100 (itself a 1976 improvement upon the design of the original reed-valved 96cc RS100 that was introduced to the United Kingdom in September, 1974, and to the USA in November, 1974) with a front disc brake and a tachometer, and was replaced in 1983 with the square-stroke, 98cc RX-S (with part numbers coded 31J), a major update on the RS design (with substantial changes particularly to the cylinder, head, and induction, and the points ignition replaced by Yamaha Capacitor Discharge Ignition) which was to form the basis of the Escort-distributed variants including the EY-100 Escort Yamaha 100. The Escort variants of the RX-S had heavier gauge steel tubing and other changes specific to the Indian market, including slotted screws instead of the original Phillips. Names of older variants of the RS line were re-used for Escort variants of the RX-S, including RX100