in the late 1940s, magnetic tape recorders were adopted by the networks to pre-record shows or repeat them for airing in different time zones, but 16-inch vinyl pressings continued to be used into the early 1960s for non-network distribution of prerecorded programming. use of the lp's microgroove standard began in the late 1950s, and in the 1960s the size of discs was reduced to 12 inches, becoming physically indistinguishable from ordinary lps.