The Advanced Computerized Execution System (ACES) is a NASDAQ subscription service paid for by market makers that allows order-entry firms trading in Nasdaq Capital Market and Nasdaq global market stocks access to a market maker's internal trading system to route to them using the ACES "Pass-Through".
ACES is a voluntary service for which market makers must register.
[2] ACES automatically sends the trade information to Automated Confirmation Transaction Service (ACT) for reporting.
Part of the evolution of ACES includes the elimination of the execution function in 1998 with the introduction of new order handling rules.
These rules encouraged Nasdaq participants to manage their order file internally rather than on ACES.