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).