The term Advanced Computerized Execution System refers to the technology used by the NASDAQ to automate trades and order entry between firms and market makers that have an established working relationship.
The Advanced Computerized Execution System, or ACES, is a subscription service offered by the National Association of Dealers Automated Quotations (NASDAQ). Following the October 1987 stock market crash, NASDAQ instituted a number of changes, including the automation of order routing through ACES in 1988.
The NASDAQ exchange is a continuous auction market in which market makers quote bid and ask prices for standard order sizes. Trading typically takes place through the Small Order Execution System (SOES) or the Advanced Computerized Execution System (ACES). Firms trading in the NASDAQ market have access into a market maker's trading system through ACES, which acts as a pass through system to confirm order entry and execution.