NEW YORK -- NFL teams used to take Polaroid pictures of plays from atop the stadium during games then send them down to the field on a rope.
Technology improved so that an automated camera could deliver the images to a printer on the sideline, creating that familiar sight of a quarterback staring at a sheet of paper to figure out what went wrong on an interception.
That was still the case last season, when fans in the stands could watch highlights on their smartphones, but players and coaches were flipping through three-ring binders of black-and-white photos.
The NFL sideline is finally catching up.
Tablets will be allowed for the first time starting with Sunday's Hall of Fame game, though they won't exactly be running the most cutting-edge apps. The devices will replicate the old system of transmitting still photos to the field -- but faster, clearer and in color.
No surfing the Web. No selfies or tweets. And more important from a football standpoint: no watching replays of the last snap.
"The purity of the game has always been not having video," Tennessee Titans coach Ken Whisenhunt said. "So when you're looking at pictures you have to sometimes guess, or a lot of times the pictures aren't what really exactly happened. That part of it is still coaching, and I kind of like that."
Indianapolis Colts tight end Dwayne Allen, though, suggested that allowing video would improve the sport by making games even more competitive. And just as instant replay, once revolutionary, is now widely accepted and has been expanded over the years, the same could take place with the tablets. Adding video is possible in the future, NFL spokesman Brian McCarthy said.
That would need to go through the league's competition committee, just as the introduction of tablets did. The NFL signed a sponsorship deal with Microsoft last year, which includes the standard promotions of sticking the league's logo on products and a more sophisticated collaboration of making NFL content available on Xbox.
But the company also became a sort of bonus IT department, engineering its Surface tablets to withstand the rigors of the NFL sideline. Searing heat in Arizona. Pouring rain in Seattle. Frigid cold in Green Bay. The screens had to be viewable in the glare of the sun.
And the devices couldn't be vulnerable to hacking -- a real concern in a league famous for paranoid coaches, where the term "Spygate" was spawned.
The tablets will be locked in a temperature-controlled cart by the NFL during the week. They'll operate on a secure wireless network in stadiums.
The specialized tablets come in a protective case with an attached grip to make holding it easier. There will be 13 on each sideline and another 12 in the coaches' box. Other than that, the only people on the sideline allowed to carry digital devices are the medical staff.
Players and coaches can zoom in on each photo and write on it, either with their finger or an attached stylus.
Sometimes with the old paper printouts, New York Jets coach Rex Ryan recalled, "you'd get them back and you're like, 'Man, what is this?"'
"This should be a lot nicer and the quality a heck of a lot better," he said.
The old paper system will remain in place, both as a backup in case the technology fails, and for those coaches and players who don't want to switch.
"I'm old school," said Ravens defensive coordinator Dean Pees, who watches games from upstairs and figures he'll keep using the hard copies because they work fine for his needs.
Still, the NFL's McCarthy predicts even the most old-school coaches -- and the league has plenty -- might be swayed if they suspect the other team is gaining an advantage. The photos will arrive to the tablets in a few seconds, and getting them even a half-minute faster is worth it to these ultracompetitive men who constantly seek the slimmest of edges.
Consider if the Ravens defense makes a stop, but then the offense immediately commits a turnover. The tablet may be the difference in Baltimore's defensive players seeing some photos of the previous series before they run back onto the field.
Washington Redskins offensive coordinator Sean McVay said the tablets would also speed up looking for, say, first-half plays during the fourth quarter.
"I'm all for trying anything new," said Denver Broncos offensive coordinator Adam Gase, "and if it can help us in any way, adjust off that."
If the tablets malfunction for one team before the game, then they're disabled for both clubs. But if they crash after kickoff, the other squad can keep using them, to prevent coaches from pretending that the devices aren't working in an attempt to gain an advantage in a game that's not going well.
The preseason offers teams a chance to test and grow comfortable with the new technology before the games start counting, and for the league and Microsoft to work out any kinks.
"Some of us dinosaurs don't change easily, but I think it has a chance to be a benefit," said Miami Dolphins coach Joe Philbin, whose staff plans to use the tablets exclusively during one exhibition as a trial run.
Many of the players, of course, have been tapping on high-tech gadgets since they were kids. Teams are using them more and more during the week.
Under Whisenhunt, for instance, the Titans have added iPads for playbooks and an extra camera in the end zone during practice for extra angles.
But on Sundays, for now, the NFL is inching forward.
"Like anything, whether it's a new vacuum cleaner or a new car, you've got to get used to it," St. Louis Rams general manager Les Snead said.
"Just because you can watch YouTube movies on your iPad," he added, "doesn't mean it's going to happen that fast."