How many letters does the top answer for “whistler was the codename of this microsoft operating system.” have?

The most common answer is windows (7 letters).

Crossword clue: whistler was the codename of this microsoft operating system.

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

windows 7 letters otdb

(trademark) an operating system with a graphical user interface

xp 2 letters otdb

The first two letters of the Greek word XRISTOS, Christ; -- an abbreviation used with the letters separate or, oftener,