(TCAM) ternary content-addressable memory

Contributor(s): Jessica Scarpati

TCAM (ternary content-addressable memory) is a specialized type of high-speed memory that searches its entire contents in a single clock cycle

The term “ternary” refers to the memory's ability to store and query data using three different inputs: 0, 1 and X. The “X” input, which is often referred to as a “don’t care” or “wildcard” state, enables TCAM to perform broader searches based on pattern matching, as opposed to binary CAM, which performs exact-match searches using only 0s and 1s.

Generally speaking, CAM is often described as the opposite of random access memory (RAM). To retrieve data on RAM, the operating system (OS) must provide the memory address where the data is stored. Data stored on CAM can be accessed by performing a query for the content itself, and the memory retrieves the addresses where that data can be found. Due to its parallel nature, CAM (and by extension TCAM) is much faster than RAM. However, it is not widely used in most electronics because it is expensive to build, consumes a lot of power and generates a high level of heat that must be dissipated.

TCAM is commonly found in networking equipment, such as high-performance routers and switches, to increase the speed of route look-up, packet classification, packet forwarding and access control list-based commands.

This was first published in September 2013

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