Participants in the stock market range from small individual stock investors to large hedge fund traders, who can be based anywhere. Their orders usually end up with a professional at a stock exchange, who executes the order.
Some exchanges are physical locations where transactions are carried out on a trading floor, by a method known as open outcry. This type of auction is used in stock exchanges and commodity exchanges where traders may enter "verbal" bids and offers simultaneously. The other type of exchange is a virtual kind, composed of a network of computers where trades are made electronically via traders at computer terminals.
Actual trades are based on an auction market paradigm where a potential buyer bids a specific price for a stock and a potential seller asks a specific price for the stock. (Buying or selling at market means you will accept any bid price or ask price for the stock.) When the bid and ask prices match, a sale takes place on a first come first served basis if there are multiple bidders or askers at a given price.
The purpose of a stock exchange is to facilitate the exchange of securities between buyers and sellers, thus providing a marketplace (virtual or real). The exchanges provide real-time trading information on the listed securities, facilitating price discovery.
The New York Stock Exchange is a physical exchange, where much of the trading is done face-to-face on a trading floor. This is also referred to as a "listed" exchange (because only stocks listed with the exchange may be traded). Orders enter by way of brokerage firms that are members of the exchange and flow down to floor brokers who go to a specific spot on the floor where the stock trades. At this location, known as the trading post, there is a specific person known as the specialist whose job is to match buy orders and sell orders. Prices are determined using an auction method known as "open outcry": the current bid price is the highest amount any buyer is willing to pay and the current ask price is the lowest price at which someone is willing to sell; if there is a spread, no trade takes place. For a trade to take place, there must be a matching bid and ask price. (If a spread exists, the specialist is supposed to use his own resources of money or stock to close the difference, after some time.) Once a trade has been made, the details are reported on the "tape" and sent back to the brokerage firm, who then notifies the investor who placed the order. Although there is a significant amount of direct human contact in this process, computers do play a huge role in the process, especially for so-called "program trading".
The Nasdaq is a virtual (listed) exchange, where all of the trading is done over a computer network. The process is similar to the above, in that the seller provides an asking price and the buyer provides a bidding price. However, buyers and sellers are electronically matched. One or more Nasdaq market makers will always provide a bid and ask price at which they will always purchase or sell 'their' stock.[2].
The Paris Bourse, now part of Euronext is an order-driven, electronic stock exchange. It was automated in the late 1980s. Before, it consisted of an open outcry exchange. Stockbrokers met in the trading floor or the Palais Brongniart. In 1986, the CATS trading system was introduced, and the order matching process was fully automated.
From time to time, active trading (especially in large blocks of securities) have moved away from the 'active' exchanges. Securities firms, led by UBS AG, Goldman Sachs Group Inc. and Credit Suisse Group, already steer 12 percent of U.S. security trades away from the exchanges to their internal systems. That share probably will increase to 18 percent by 2010 as more investment banks bypass the NYSE and Nasdaq and pair buyers and sellers of securities themselves, according to data compiled by Boston-based Aite Group LLC, a brokerage-industry consultant.
Now that computers have eliminated the need for trading floors like the Big Board's, the balance of power in equity markets is shifting. By bringing more orders in-house, where clients can move big blocks of stock anonymously, brokers pay the exchanges less in fees and capture a bigger share of the $11 billion a year that institutional investors pay in trading commissions.