Nasdaq allows multiple market participants to trade through it's electronic communications networks (ECNs) structure, increasing competition. The Small Order Execution System (SOES) is another Nasdaq feature, introduced in 1984, to ensure that in 'turbulent' market conditions small market orders are not forgotten but are automatically processed.
Nasdaq began trading on February 8 1971. It became the largest stock market in the US by volume in 1999.
NASDAQ stands for National Association of Securities Dealers Automated Quotations.