String matching plays a central role in content inspection applications such as intrusion detection, anti-virus, anti-spam and Web filtering. Because they are computation and memory intensive, software matching algorithms are insufficient in meeting the high-speed performance. Thus, offloading packet content inspection to dedicated hardware seems inevitable. This paper presents a scalable automaton matching (SAM) design, which uses Aho-Corasick (AC) algorithm with two parallel acceleration techniques, root-indexing and pre-hashing. The root-indexing can match multiple bytes in one single matching, and the pre-hashing can be used to avoid bitmap AC matching, which is a cycle-consuming operation. In the implementation of the Xilinx Vertex4P FPGA platform, the proposed hardware architecture can achieve almost 10.7 Gbps and support the largest pattern set, which is 7.65 times faster than the original bitmap AC in the average case. Further, SAM is feasible for either internal or external memory architecture. The internal memory architecture provides high performance, and the external memory architecture provides high scalability of patterns.