For Multitaskers, Multiple Monitors Improve Office Efficiency Workers in the digital era can feel at times as if they are playing a video game, battling the barrage of e-mails and instant messages, juggling documents, Web sites and online calendars. To cope, people have become swift with the mouse, toggling among dozens of overlapping windows on a single monitor. But there is a growing new tactic for countering the data assault: the addition of a second computer screen. Or a third. This proliferation of displays is the latest workplace upgrade, and it is responsible for the new look at companies and home offices - they are starting to resemble mission control. For multiscreen multitaskers, a single monitor can seem as outdated as dial-up Internet. "You go back to one, and you feel slow," said Jackie Cohen, 42, who uses three 17-inch monitors in her home office in San Francisco, where she edits a blog about Facebook. Her center screen shows what she is writing or editing, along with e-mail and instant messages; the left and right monitors display news sites, blogs and Twitter feeds, and she keeps 3 to 10 tabs open on each. One monitor recently broke, and she felt hamstrung. "I don't want to miss seeing something," Ms. Cohen said. Her computer seemed to work a bit faster with one monitor fewer, she said. But her brain was a different matter. "I can handle it," she added. I'm sure there are people who can't. Certainly more people are trying. Tech firms sold 179 million monitors worldwide last year and only 130 million desktop computers - meaning "more screens per desk," said Rhoda Alexander, who heads monitor and tablet research at IHS iSuppli. Monitors are bigger, too. The average monitor sold worldwide is 21 inches, up from 18 inches five years ago, according to iSuppli. NEC Display, a major supplier of monitors, said 30 to 40 percent of the employees of its corporate customers now used more than one monitor, up from 1 percent four years ago. There are many reasons for the spike in sales: monitors are much cheaper ($200 to $300 for a 24-inch display today compared with $700 five years ago); they are slimmer, too, so desks can accommodate more of them; and there are more communication tools - instant messaging, Twitter, Facebook - that workers have to keep an eye on (or at least feel they should). More and bigger screens can convey bragging rights, too. Tech companies use them as recruiting tools, said Chuck Rossi, 45, who uses three monitors (27-inch, 30-inch and a 17-inch laptop) to toggle among dozens of tabs for his engineering job at Facebook, where he checks hundreds of software updates to the site each day before they become public. "Companies will pitch it" to job candidates, Mr. Rossi said. They know real estate is important. It shows they are serious about their engineers. And the engineers do care about the screens, he said, noting that someone might tell a friend about a new job by adding, "They're giving me a 30 right off the bat," which is shorthand for a 30-inch monitor. The main rationale for a multimonitor setup is that it increases productivity. But that notion is not simple to prove or measure, partly because it depends on the kind of work people do and whether they really need to be constantly looking at multiple data streams. Another theory holds that people have just grown so addicted to juggling that having more monitors simply creates a compulsion to check them. One study, by the University of Utah, found that productivity among people working on editing tasks was higher with two monitors than with one. The study was financed with about $50,000 by NEC Display, which had hoped to find evidence that companies should buy more monitors to increase productivity. Other tech companies also promote multiple displays - one Hewlett-Packard ad declares that "two is better than one." The author of the study, James A. Anderson, a professor of communication, said he had not been influenced by NEC's financing. He said he uses three monitors himself, but also said that it was hard to generalize about whether more monitors are better.