Three-by-five index cards, those hallmarks of research, may be fading away in these digital times, but the need to take notes endures.
Human memory is as weak as ever, and people are still shoring it up by recording their observations, research and grocery lists, though many now use computers instead of pens and paper.
But the electronic notepads on smartphones, tablets, laptops and desktops don't synchronize with one another automatically. Say you're sitting on a plane with your laptop, jotting down some brilliant words for that speech you're giving next week. Back at the office, those notes will never find their way to the copy of the speech you've stored on your desktop, unless, for example, you e-mail them to yourself.
Now companies including Simperium and Evernote offer applications you can install on your various mobile and stationary devices. The companies' servers gather and coordinate those notepads, keeping all the entries up to date
The source of the notes may be typed text, Simperium's specialty. Evernote's expanding services, meanwhile, can handle notes sent by keyboard, digital pen, scanner or camera phone.
Simplenote, a free application from Simperium, runs on desktops and laptops via the Web. It can also be installed on iPhones, iPads and the iPod Touch, says Michael Johnston, a co-founder of Simperium, a start-up begun this year in San Francisco. Other companies, he says, also use Simperium's synchronization platform as part of apps that run, for instance, on Android phones.
The company is already profitable, he said, in part from premium subscriptions ($12 a year) and in part from advertising displayed on the site.
Jonathan Beilin, a game developer and writer in Sunnyvale, Calif., uses Simplenote with his desktop PC, his Apple laptop, his iPad and his iPhone. He may write down ideas for his blog in the morning on his iPad; then, when he switches to his laptop later in the day, the rough draft is waiting for him.
"It's the only sane way to share between my computers and my mobile devices," he said. (He still carries pencils and a Moleskine notebook, mainly for drawing.)
The Simplenote app is intended for keeping text notes. For those who want to capture additional information -- like Web page clippings, photos and voice memos -- Evernote offers both a free and a premium service ($45 a year) that work across most devices and platforms, says Phil Libin, the C.E.O. of the company, which is in Mountain View, Calif. If users are away from home without laptops, they can still use a smartphone or a hotel computer, for instance, to access an account and retrieve notes.
Mr. Libin says Evernote has been adding and refining its offerings, buoyed in part by $20 million in recent funding led by Sequoia Capital. One of its new services, available to those who install Google's Chrome browser, is a dual search -- one of public sources found by Google, and another of the private data on a user's Evernote account. It also added one-button service on scanners from Canon and other companies that automatically send scanned documents to the Evernote account.
David Pierce, 22, a junior analyst at PC Magazine in Manhattan, uses Evernote on his BlackBerry, iPad, iPod Touch, Mac and PC. "I take notes on whatever device I have in hand at the moment," he says, "but then all the information in my notes is in one, single, accessible place."
He also uses his phone to take photos of business cards and white boards at meetings, and sends them to his Evernote account, which is equipped to decipher the printed and handwritten text.
"I use it as my own personal scanner," he says. "I don't have to retype business cards, and all of the text is searchable."
Customers can opt for the free version, with limits on storage, but Megan Soto, an account executive at Maxwell PR Studio in Portland, Ore., chose the premium service and the extras it offered because she had just moved to the city and a new apartment. "I don't even have a file cabinet yet," she says. "So I put everything there."
She scanned the apartment lease, for example, and dropped it into the application, along with pictures of books she might buy later. Mainly, though, she uses it to clip and save Web content. "Even if a site is taken down later," she says, "I will still have the information."
Web-clipping is the most popular activity among Evernote users, whose numbers have grown to more than 4.8 million worldwide, Mr. Libin says. Most users reach their accounts from two or more places, typically including a home computer, a phone, or a computer at work or school. IPads, only recently on the market, already account for about 18 percent of the company's mobile traffic.
Mr. Pierce at PC Magazine says the dual search function came in handy when he was working on a new research project. He found he had already accumulated and stored in Evernote a good portion of the needed information. And he was amazed at how much he recalled as he read through it.
This kind of recollection is one of the primary benefits of notes, says Dr. Richard R. Yeo, a professor at Griffith University in Brisbane, Australia, and an expert on note-taking as it developed in 17th-century Europe.
"Notes are an external cue to internal memory," he says. "You may need a prompt to start the recollective search," he said. "A notebook or notes may provide that prompt."