The first prerecorded reel-to-reel tapes were introduced in the United States in 1949; the catalog contained fewer than ten titles with no popular artists. In 1952, EMI started selling pre-recorded tapes in Great Britain. The tapes were twin-sided and mono (2 tracks) and were duplicated in real time on modified EMI BTR2 recorders. RCA Victor joined the reel-to-reel business in 1954. In 1955, EMI released 2-track "stereosonic" tapes, although the catalog took longer to be published. Since these EMI tapes were much more expensive than a vinyl LP record, sales were poor; still, EMI released over 300 "stereosonic" titles. Then they introduced their Twin Packs, which contained the equivalent of two LP albums but playing at 3.75ips.