A specialized memory structure is provided for storing parts of orders received at an electronic trading system. A received order is divided into a displayed portion and a non-displayed portion, and each portion is allocated to a respective part of the memory structure. The memory structure is configured such that while matching the order with a contra order, priority is given to the displayed portion over the non-displayed portion. If such a match occurs, the displayed portion may be replenished. The matching in the non-displayed portion generally occurs according to rules of applying discretion. The matching in the displayed portion may occur at the displayed price or according to the rules of discretion.