Advertisements, jingles, and the top-of-hour station identification required by law were commonly stored on Fidelipac endless-loop tape cartridges, known colloquially as "carts". These were similar to the consumer four-track tapes sold under the Stereo-Pak brand, but had only two tracks and were usually recorded and played at 7.5 tape inches per second (in/s) compared to Stero-Pak's slower 3.75 in/s. The carts had a slot for a pinch roller on a spindle which was activated by solenoid upon pressing the start button on the cart machine. Because the capstan was already spinning at full speed, tape playback commenced without delay or any audible "run-up". Mechanical carousels would rotate the carts in and out of multiple tape players as dictated by the computer. Time announcements were provided by a pair of dedicated cart players, with the even minutes stored on one and the odd minutes on the other, meaning an announcement would always be ready to play even if the minute was changing when the announcement was triggered. The system did require attention throughout the day to change reels as they ran out and reload carts, and thus became obsolete when a method was developed to automatically rewind and re-cue the reel tapes when they ran out, extending 'walk-away' time indefinitely.