N concert, Mark Zeltser's fingers seem to defy the laws of physics, attacking the piano keyboard with such speed and energy that they become a blur. A critic for Le Figaro in Paris once wrote: "Zeltser's hands are as powerful as a steelworker's, while his fingers have the brilliant agility of butterflies."

The Soviet-born pianist has put those fingers to work on a different kind of keyboard, and not to make music. His stated goal is to offer, by Internet-connected computer, every classical note ever written. "Virtually every note," he hedged, pleased with his play on words as he described his new Web site, everynote.com, which offers sheet music for more than 4,000 compositions for piano and violin by 160 composers.

"As a professional musician, I can assure you that we have at least 99 percent of major composers' works" for piano and virtually all for violin, he said, not to mention obscure pieces and composers. Bramwell Tovey, music director of the Vancouver Symphony and Luxembourg Philharmonic, was surprised to find works of the lesser-known Moritz Moszkowski as well as giants like Mozart.

Mr. Zeltser, who holds a doctorate from the Moscow State Conservatory, started up the site this spring with piano literature and added a violin section last month after waiting more than a decade for the technology to catch up with a brainstorm he had on a six-week tour in Australia. On that trip, the smaller of two suitcases contained his wardrobe; the big, heavy suitcase was filled with his music. He began to dream of classical sheet music instantly available anywhere in the world.

"I seriously went to work on the idea, but the idea was ahead of the technology," he said, remembering hard drives as bulky as his suitcase full of scores, and scanners that lacked the resolution needed for printouts in which a speck can change the tempo.

After marrying a Russian computer programmer, Mr. Zeltser realized almost four years ago that the technology had become available to create a niche site for professional musicians and master teachers like himself. He and his wife, Violetta, began building the site in a bedroom in their apartment on the Upper West Side of Manhattan.

They followed his original concept of scanning in classical sheet music and allowing the first page to be viewed before being purchased and printed out. Unlike some sites with sheet music, Everynote requires no special software beyond Adobe Reader 5.0 or later. Russian immigrants in Brooklyn designed the site, but Mr. Zeltser selected every entry; most are accompanied by a brief biography of the composer.

Copyright was the least of the challenges he faced. Most of the works played by concert artists like Mr. Zeltser are in the public domain, which under American law includes editions published before 1923, among them works by "modern" composers like Prokofiev, Stravinsky and Bartãk as well as the familiar Bach, Beethoven, Grieg, Liszt and Mozart.

"Naturally, 95 percent of our library consists of the works created in the 18th and 19th centuries," he said. "The difficult part was to find publications before 1923 in good condition."

The quest for complete and clean scores suitable for scanning took him to public libraries in New York, Los Angeles and Fort Lauderdale, Fla., where he also maintains a home. The New York collection was bigger than those in the other cities but showed the wear and tear of frequent use and often required tracking down two or three copies to achieve one digital version. In Los Angeles he found 19th-century sheet music that looked as though it had been "printed yesterday." In Fort Lauderdale he discovered an 1876 edition of Beethoven's Bagatelles that appeared brand-new.

How such sheet music arrived in Fort Lauderdale, a city not incorporated until 1911, puzzled Mr. Zeltser. "Instead of throwing out the music, perhaps someone gave it to the library," he said.

About 30 percent of the music on the site comes from European sources, particularly the former Soviet Union, where the Stalinist era left an unexpected legacy for musicians. Even small towns of 20,000 inhabitants, he said, were required to maintain musical libraries equal to what could be found in Moscow. He discovered a trove of untouched scores and transcriptions by legendary Russian musicians.

He arranged for the music to be photocopied and shipped to him by weight rather than by the piece. "Sometimes we would get 40 kilos, because the people there didn't know music," he said.

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Having been a child prodigy in mathematics and music and winner of international prizes like the Marguerite Long-Jacques Thibaud Competition in Paris, Mr. Zeltser needed no help in evaluating the scores, although his mother, Bertha, a concert pianist and daughter of a concert violinist, did make space in her East Side apartment for a sophisticated scanner. His daughter, Elizabeth, a violinist in the New York Philharmonic, consulted on the violin section.

Mr. Zeltser has kept his personal life private. The Everynote site says only that professional musicians created it. His own site, markzeltser.com, has a discreet Everynote icon under a column of his record album covers, which include the Beethoven concerto for piano, violin, cello and orchestra with Anne-Sophie Mutter, Yo-Yo Ma and Herbert von Karajan, who introduced Mr. Zeltser to the West in the late 1970's.

Today, at age 56, he spends the concert season on tour: this fall he will travel to Europe, Latin America, Japan and Korea after performing next month with his daughter at the Chautauqua Institution in western New York. He is also recording works of Prokofiev with the Moscow Symphony.

He makes time for Everynote, he said, because he wants classical sheet music to be more widely available and affordable, but that doesn't mean he doesn't want to make money, particularly since he has invested $300,000 in the project. He hopes to attract buyers through his pricing: mostly under $5, for music that might cost 3 to 10 times as much elsewhere.

Mr. Zeltser does seem to have struck a chord with fellow musicians. Glenn Dicterow, concertmaster of the New York Philharmonic and a faculty member at the Juilliard School and the Manhattan School of Music, likened the site to an online music store like Apple's iTunes in its immediate gratification. "If the teacher wants a student play a Beethoven sonata, the student can get started right away without having to go somewhere to fetch it," he said.

Furthermore, he said, students cannot use the excuse that music is unavailable, nor must they rely on library copies marked up by someone else.

And not only the more advanced students are affected. Lisa Muratore, a Dallas piano teacher who teaches children under age 10, had no idea who was behind Everynote when she replied to a promotional e-mail message by writing: "This is a piano teacher's dream. Now we don't have to buy an entire book just to get one piece."

Mr. Zeltser plans to introduce other instruments, voice, chamber music, orchestral works and new composers as fast as he can scan. Bowing to requests from site visitors, he will add the classical guitar next, although he he was surprised to find that the classical guitar seems more popular than the flute.

So far responses have come mostly from people in the United States, Western Europe and Japan, but he has also received inquiries from China, Vietnam and Bulgaria. Technology has caught up with his ideas, but not e-commerce. Many of the musicians who crave classical sheet music use the Internet. They just don't have credit cards.