A high-speed string-search engine

A character string search engine (SSE) for rapid text retrieval has been developed. The SSE accommodates a novel string-search architecture which combines a 512-stage finite-state automaton (FSA) logic with a recently developed content addressable memory (CAM) to achieve an approximate string comparison of 80 million strings per second. The CAM cell consists of four conventional static RAM (SRAM) cells and a read/write circuit. Concurrent comparison of 64 stored strings with variable length has been achieved in 50 ns for an input text stream of 10 million characters/s, permitting performance despite the presence of single character errors in the form of character codes. Furthermore, this chip allows nonanchor string search and variable-length `don´t care´ (VLDC) string search. The SSE chip has 217600 transistors in an 8.62×12.76-mm die area. The technology used was a double-metal 1.6-μm n-well CMOS process.