The NFL runs dozens of computers for 24 hours a day for 12 weeks to evaluate its millions of possible schedule combinations. Each team's opponents are set at the end of the previous season based on records and the rotation of interdivision matchups. The puzzle is determining which week each game will be played, and which TV slot it will slide into.

Close to 20,000 "rules" are programmed in to let the machines know which outcomes should be avoided — everything from dates that stadiums aren't available to keeping a team from playing four straight road games.

Undesirable options are inevitable, though, with some worse than others. So "penalties" are assigned to help the software minimize the unhappy teams. The computers go through each possible schedule to determine which racks up the fewest penalties.

The league, which used to do the schedule by hand, started using computers in 2002 and now relies on a program designed by British Columbia-based Optimal Planning Solutions.

Plenty of human judgment comes into play, too. NFL executives look to slot high-profile games on national TV and plug those preferences in. Sometimes coaching changes and free agency moves that take place after the process started suddenly make a matchup more or less appealing, and that needs to be entered in.

Officials evaluate the suggested schedules that the machines compile to settle on the one they like the best. Commissioner Roger Goodell has final approval.

A sampling of the considerations taken into account:

— Because each team now must play a Thursday night game, it gets a sort of "mini-bye" afterward — at least 10 days until its next outing. The NFL tries to ensure that a club's official bye and mini-bye don't come too close together so players get the most out of the extra rest each time.

— Speaking of byes, teams worry about the competitive disadvantage of facing an opponent coming off extra rest and preparation time. NFL research found there's no harm for a club hosting a foe that didn't play the previous weekend — it wins those matchups at the same rate for all home teams. But for squads that go on the road to play an opponent coming off a bye, their winning percentage decreases by more than one-fifth. So the NFL focuses on preventing a team from encountering that scenario more than once.

— In determining which imperfect option is fairest, the league looks to the past. If a team is going to be stuck with playing three straight road games, it should be one that hasn't been saddled with that burden in a long time. That's little comfort, though, to a new coach or general manager staring down that schedule. In other cases, there are ways to try to minimize the difficulty. If a team must play on Thursday night after an away game, the goal is to at least make it a short road trip.

— The NFL switched to divisional matchups for "Thursday Night Football" this season to try to solve several problems. With the short week to prepare, teams already are familiar with each other, and the travel is shorter. Plus, with CBS adding Thursday night games this year, divisional matchups also offer the appeal of heated rivalries that draw viewers.