rank and file (n.)

early 14c., "row, line, or series;" c. 1400, a row of an army, from Old French renc, ranc "row, line" (Modern French rang), from Frankish *hring or some other Germanic source (compare Old High German hring "circle, ring"), from Proto-Germanic *hringaz "circle, ring, something curved" (from nasalized form of PIE root *sker- (2) "to turn, bend").

Meaning "a social division, class of persons" is from early 15c. Meaning "high status or position in society" is from early 15c. Meaning "a relative position" is from c. 1600. Sense of "one of the rows of squares across a chess board" is by 1570s. Military ranks "the body of private soldiers" is attested by 1809.

1520s, "string or wire on which documents are strung," from French file "a row" (15c.), noun derived from filer "string documents; spin thread" (see file (v.1)). The literal sense explains why from the beginning until recently things were generally on file (or upon file). The meaning "collection of papers systematically arranged for ready reference" is from 1620s; computer sense is from 1954. The sense "row of persons or things one behind another" (1590s) is originally military, from the French verb in the sense of "march in file." Meaning "line of squares on a chessboard running directly from player to player" is from 1610s.