Bob Glauber Newsday columnist Bob Glauber

Bob Glauber has been Newsday's national football columnist since 1992. He was Newsday's football writer covering the Jets

To get an idea of just how impatient NFL owners have become with hiring and firing coaches, consider this: If Tom Landry were starting out today, it is a virtual certainty that he would never have gotten the chance to produce a Hall of Fame career.

Landry took over the expansion Cowboys in 1960 and didn’t have a winning record for six consecutive seasons — a virtual eternity by today’s what-have-you-done-for-me-lately pressure on coaches.

“In today’s NFL, he’d probably be fired,” said Gil Brandt, the Cowboys’ longtime personnel director, who started with the Cowboys the same year Landry did.

The coaching merry-go- round in the NFL has operated at warp speed in recent years, with a whopping seven head-coaching changes in each of the last four years. That’s a combined 28 changes in a 32-team league, an unprecedented turnover rate that shows no signs of slowing down as owners seek ways to turn their fortunes around quickly.

Brandt recalled the time Cowboys owner Clint Murchison showed the kind of commitment toward Landry that would be unthinkable by today’s standards. After the Cowboys won a total of 13 games in Landry’s first four seasons, he was given a 10-year contract extension.

“ said, ‘I can fire him and pay him off, but I’m not going to find a better coach,’ ” Brandt said.

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Murchison’s patience eventually paid off, and by 1971, Landry had won the first of two Super Bowl titles and was well on the way toward Canton.

But that kind of resolve is almost nonexistent in today’s game. The most recent expansion team, the 2002 Houston Texans, replaced coach Dom Capers after four seasons. Before that, after resuming play in 1999, the Cleveland Browns waited only two years to fire Chris Palmer.

The turnover rate continues unabated, and now the Giants are part of the equation after parting ways with Tom Coughlin. But at least Coughlin, who is set to interview with the Eagles tomorrow, got 12 seasons before the Giants were ready to move on. How about the Class of 2014: Of the seven coaches hired two years ago, three already have been fired, including Lovie Smith, who was told over the phone Wednesday night that he would not be retained.

Another coach from that class, Detroit’s Jim Caldwell, remains employed, but his fate will be decided by Bob Quinn, who was named general manager Friday night.

Even the prevailing theory that coaches of quarterbacks who are drafted high in the first round are given more time to develop their young passers is out the window. Smith’s Buccaneers drafted Jameis Winston No. 1 overall last year, and Ken Whisenhunt’s Tennessee Titans took Marcus Mariota with the No. 2 pick. Both coaches now are gone.

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Bill Belichick of the Patriots, hired in 2000, is the longest-tenured coach. Coughlin had held the next spot before stepping down Monday after his second straight 6-10 season and his fourth consecutive year of missing the playoffs. The main reason for the change: There was a feeling among Giants ownership that 12 years was long enough for the 69-year-old coach and that the team needed a new voice.

Another symptom of today’s impatience: Owners are more than willing to cast their lot with recycled head coaches, figuring a change of scenery might work. Consider: Two years after Smith was fired by the Bears, the Bucs hired him. Whisenhunt was cut loose by the Cardinals in 2013 but landed in Tennessee a year later. And after being fired by the Broncos in 2014, John Fox quickly was snapped up by the Bears before the 2015 season.

The Steelers probably are the best example of relying on an institutional system of coach stability. The team has had only three head coaches in the last 47 seasons: Chuck Noll for 23, Bill Cowher for 15 and Mike Tomlin for nine.

“People used to retain coaches because they couldn’t afford to pay them off,” Brandt said. “Now, with the money they’re able to generate, they can afford to pay them off like it’s petty cash.”

Unlike baseball, basketball and hockey, in which frequent coaching and managerial changes have been the norm for years and hirings and firings often lead at least temporarily to better results, football is a far more complicated sport that relies on sophisticated systems that require time and patience to bear fruit. But many owners simply don’t have the stomach to keep coaches in place, especially after losing seasons.

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Browns owner Jimmy Haslam, for instance, fired Mike Pettine after only two seasons. Pettine had replaced Rob Chudzinski, who lasted only one season. Whoever succeeds Pettine will become the ninth coach in 18 seasons, and the Browns have been in only one playoff game in that span. One.

The Dolphins have had eight coaches during the last 12 seasons and they, too, have been in only one playoff game in that time. Adam Gase, hired Saturday, becomes coach No. 9.

The teams that have shown patience generally have been rewarded. Belichick, who has the luxury of coaching arguably the greatest quarterback of all time in Tom Brady, has been to the Super Bowl six times and won four. During Coughlin’s tenure with the Giants, there were some seasons in which his status appeared in doubt, but he responded with two Super Bowl victories, handing Belichick his only two losses.

The Steelers have won six Super Bowls in the Noll-Cowher-Tomlin era.

And though the Panthers haven’t won a championship yet, they produced the league’s best record this season at 15-1 under coach Ron Rivera. Go back to Rivera’s second season in 2012, when he finished 7-9, and there were questions about his tenure. But team owner Jerry Richardson, who won the NFL championship in 1959 with the Baltimore Colts and caught a pass from Johnny Unitas in the title game, has long been a believer that patience is required, even in today’s demanding environment.

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Many of his fellow owners don’t subscribe to that theory and think changing the coach is the way to go. Unfortunately, they often wind up disappointed with the results.