Content-addressable memory core cells - A survey

The data stored in a content-addressable memory (CAM) are accessed based on their contents, rather than their location, and this functionality is useful in many applications, including databases, table look-up, and associative computing. The central building blocks of these memories are the core cells, and this paper surveys 14 such cells, primarily from a qualitative perspective. The cells date from 1970, and many innovations have been introduced since then, both in circuit design and fabrication technology. Among the cells described, 11 employ static storage and four use dynamic storage; 14 can be implemented in CMOS, while one requires BICMOS technology. A discussion follows, highlighting significant design improvements, advocating particular cells for general-purpose use, and suggesting avenues for future research.