Wire-speed processing of bit streams at any rate is promised by the PAX.core 1000, which is claimed as the industry's first Gigabit classifying core for high-speed network processor-based systems. The core, coupled with memory, performs both simple and complex packet parsing and field lookups, independent of additional co-processors. The core implements a highly programmable state machine engine processor with optional functional units such as host interface, checksum calculation and configurable counters.