airtime than network affiliates, syndicated shows are usually edited to make room for extra commercials. Often about 100 episodes (four to five seasons' worth) are required for a weekly series to be rerun in daily syndication (at least four times a week). Very popular series running more than four seasons may start daily reruns of the first seasons, while production and airings continue of the current season's episodes; until approximately the early 1980s, shows that aired in syndication while still in production had the reruns aired under an alternate name (or multiple alternate names, as was the case with Death Valley Days) to differentiate the reruns from the first-run episodes. Few people anticipated the long life that a popular television series would eventually see in syndication, so most performers signed contracts that limited residual payments to about six repeats. After that, the actors received nothing and the production company would keep 100% of any income until the copyright expired; many shows did not even have their copyrights renewed and others were systematically destroyed, such was the lack of awareness of the potential for revenue from them. This situation went unchanged until the mid-1970s, when contracts for new shows extended residual payments for the performers, regardless of the number of reruns, while tape recycling effectively came to an end (rapid advancements in digital video in the 1990s made preservation far more economical) and the Copyright Act of 1976 extended copyright terms to much longer lengths, eliminating the need for renewal. Once a series is no longer performing well enough to be sold in syndication, it may still remain in barter syndication, in which television stations are offered the program for free in exchange for a requirement to air additional advertisements (without compensation) bundled with the free program during other shows (barter syndication is far more common, if not the norm, in radio, where only the most popular programs charge rights fees). The Program Exchange was once the most prominent barter syndicator in United States television, offering mostly older series from numerous network libraries. Barter syndicated series may be seen on smaller, independent stations with small budgets or as short-term filler on larger stations; they tend not to be as widely syndicated as programs syndicated with a rights fee. Classic television With the growing availability of cable and satellite television channels as well as over-the-air digital subchannels, combined with a growing body