IEEE Micro. 12 6 : 68-78. Doi:10.1109 40.180249

Content material-addressable memory (CAM) is a particular sort of pc memory used in certain very-high-speed looking out purposes. It is also called associative memory or associative storage and compares input search information towards a desk of stored knowledge, and returns the handle of matching data. CAM is steadily used in networking gadgets the place it speeds up forwarding data base and routing table operations. This kind of associative memory is also used in cache memory. In associative cache memory, both address and content material is saved aspect by side. When the deal with matches, the corresponding content is fetched from cache memory. Dudley Allen Buck invented the idea of content-addressable memory in 1955. Buck is credited with the concept of recognition unit. Not like commonplace computer memory, random-entry memory (RAM), by which the consumer provides a memory address and the RAM returns the info word stored at that tackle, a CAM is designed such that the person supplies a knowledge phrase and the CAM searches its whole memory improvement solution to see if that knowledge phrase is saved anyplace in it.



If the information word is found, the CAM returns an inventory of a number of storage addresses where the phrase was discovered. Thus, a CAM is the hardware embodiment of what in software phrases can be referred to as an associative array. A serious interface definition for CAMs and other community search engines was specified in an interoperability agreement called the Look-Aside Interface (LA-1 and LA-1B) developed by the Network Processing Discussion board. Quite a few units conforming to the interoperability settlement have been produced by Integrated Device Know-how, Cypress Semiconductor, IBM, Broadcom and others. On December 11, 2007, the OIF revealed the serial look-aside (SLA) interface agreement. CAM is far sooner than RAM in data search functions. There are value disadvantages to CAM, however. Unlike a RAM chip, which has simple storage cells, every particular person memory bit in a completely parallel CAM must have its own related comparison circuit to detect a match between the stored bit and the enter bit. Moreover, match outputs from every cell in the information phrase should be combined to yield a whole data word match sign.



The additional circuitry will increase the bodily measurement and manufacturing value of the CAM chip. The extra circuitry additionally increases power dissipation since each comparison circuit is energetic on every clock cycle. Consequently, CAM is used solely in specialized applications where looking speed can't be accomplished using a much less pricey methodology. One profitable early implementation was a Normal Goal Associative Processor IC and System. MOSAID introduced CAM merchandise targeting networking applications. These products had been labelled Network Serps (NSE), Community Search Accelerators (NSA), and Information-based mostly Processors (KBP) but were primarily CAM with specialized interfaces and features optimized for networking. Presently Broadcom affords a number of households of KBPs. To realize a distinct stability between velocity, memory measurement and cost, some implementations emulate the perform of CAM by using standard tree search or hashing designs in hardware, using hardware tricks like replication or pipelining to hurry up effective efficiency. These designs are often utilized in routers. The Luleå algorithm is an efficient implementation for longest prefix match searches as required in web routing tables.



X or memory improvement solution don't care for a number of bits in the stored word, thus including flexibility to the search. For instance, a saved phrase of 10XX0 in a ternary CAM will match any of the 4 search words 10000, 10010, 10100, or 10110. The added search flexibility comes at an additional price over binary CAM as the internal memory cell must now encode three doable states as an alternative of the two for the binary CAM. This additional state is typically applied by including a mask bit (care or do not care bit) to each memory cell. In 2013, IBM fabricated a nonvolatile TCAM using 2-transistor/2-resistive-storage (2T-2R) cells. A design of TCAM using hybrid Ferroelectric FeFET was not too long ago published by a group of International scientists. Content-addressable memory is commonly used in pc networking devices. For example, when a network change receives an information body from one of its ports, it updates an internal table with the frame's supply MAC handle and the port it was received on.