The New York Stock Exchange voted to acquire a Chicago-based electronic stock-exchange company, Archipelago Holdings Inc., in a historic step that will transform the 213-year-old Big Board from a tradition-bound concern owned by and for its members to a profit-seeking, publicly traded company expected to compete in the evolving world of electronic markets.

The yes vote, which had been expected, was unveiled before 200 or so of the exchange's members, who crowded into a high-ceilinged boardroom at the marble building at Wall and Broad streets. About 90 percent of the Big Board's 1,366 members voted, and 95 percent of those voted in favor of the merger.

Observers and historians said that retail investors might not notice much difference immediately but that the Big Board's transformation will bring a larger number of buyers and sellers together in a more transparent setting, making for more efficient trades. As the newly merged company battles with competitors, the costs of making a trade are expected to come down.

"Larger hubs of buyers and sellers combined together make it easier for them to find one another," said Bill Cline, head of the global markets practice of Accenture Ltd., a consulting firm.

"The benefits will go to those that trade in size," said Benn Steil, director of international economics at the Council on Foreign Relations. "But there's no doubt retail investors will benefit."

Big Board chief executive John A. Thain, who announced the deal in April, had relentlessly sold it over the objections of a small but vocal group of members who had questioned its fairness.

James Rutledge, an NYSE member who attended the meeting and voted in favor of the merger, said the mood mixed exuberance with melancholy.

"When you're introduced as 'James Rutledge, New York Stock Exchange member,' that has a certain cache," he said. " 'Jim Rutledge, stockholder,' doesn't have the same spin."

The deal, which will create publicly traded NYSE Group Inc. (symbol NYX) upon closing in January, promises to dramatically change the nation's dominant stock market, which has been known for its trademark floor brokers and specialists in multicolored coats barking bids and offers.

Floor brokers and others defended the old regime's "open outcry" system as a way for investors to get the best prices available for a trade. But increasingly, large institutional investors chafed at the system, which they said took so long that prices moved before big block trades could be executed and allowed members to use information about big orders to profit for their own accounts.

As a result, the Big Board had been losing market share of trades of companies listed on the NYSE, as big investors sought faster, more efficient markets. The combination of the Big Board's heft and Archipelago's well-regarded technology is expected to improve the prospects of both concerns.

New York Stock Exchange seats, which trade according to supply and demand, recently sold for a record $4 million after trading for less than $1 million as recently as January. Sales of seats on the exchange will end Dec. 31. Archipelago shares, which traded below $20 in March, closed Tuesday at $59.95, down 43 cents.

Still to be determined is the fate of the Big Board's floor brokers and specialists. Thain has repeatedly insisted that they will remain and that the Big Board's "hybrid model" will allow specialists to better fulfill their role of buying and selling when markets are out of balance.

"The other question that I always get, which I just want to address up front, is the comment about, 'Well, gee, is the trading floor going to continue to exist over time?' " Thain told an industry group last month. "My answer to that question is, absolutely, the floor is going to continue to exist because it adds value."

But experts say that with shareholders, not members, owning the company, the push toward a less costly and faster electronic-based system will be irresistible, spelling the eventual end of trading floor altogether. "Eventually, it will be the NYSE Condos, or they'll keep it for a museum or something," said Charles R. Geisst, author of "Wall Street, a History."

The vote Tuesday vote came more than two centuries years after a group of merchants signed a trading agreement under a Buttonwood tree in lower Manhattan, forming what would become the New York Stock Exchange. The NYSE became the symbolic home of global capitalism.

Dick Grasso, the exchange's voluble chairman from 1995 to 2003, became one of the heroes of Sept. 11, 2001, helping reopen the floor just four trading days after terrorists destroyed the World Trade Center and turned Lower Manhattan into a dust-choked hellscape.

But the exchange hit a challenging stretch beginning in the summer of 2003, after Grasso was forced to resign after the not-for-profit NYSE disclosed it had paid him a lump sum of $139.5 million, mostly covering his eight years as chairman. New York Attorney General Eliot L. Spitzer filed suit against Grasso, demanding he return a large portion of the money. The case is expected to go to trial next year.

In March 2004, a group of five specialist firms agreed to pay $241.8 million to settle charges that their floor traders, who manage trading in individual NYSE-listed stocks, used their access to pricing information to profit for themselves at the expense of investors.

As the scandals unfolded, the NYSE also came under intense pressure from big mutual fund companies and other institutional investors to speed up trading. The large institutions complained that in the time it took them to complete big orders on the NYSE floor, stock prices could move against them, harming their investors. The NYSE, which has traditionally dominated trading of its own listed stocks, began to see its market share decline as more traders used electronic exchanges, such as Archipelago, to fill their orders.

Thain, a former Goldman Sachs & Co. president who took over the NYSE in January 2004, quickly began pushing for more electronic trading, an effort that culminated with the Archipelago deal. At the time, Thain said the merger would allow the new NYSE Group to more nimbly compete with Euronext, Deutsche Boerse and other global exchanges in the trading of options, derivatives and other increasingly popular exotic securities.

But foreign competition aside, the vote primarily sets up a fresh battle in the long and often bitter war for stock listings and trading volume between the NYSE and Nasdaq Stock Market Inc., which earlier this year acquired Instinet Group Inc.'s electronic-trading network. Nasdaq's stock has more than quadrupled this year.

With the acquisition, the costs of making a trade are expected to decline for investors as the newly merged company deals with its competitors.

New York Stock Exchange members voted to acquire Archipelago Holdings Inc., transforming the historic exchange.