IEEE Micro. 12 (6): 68-78. Doi:10.1109/40.180249 > 자유게시판

• 목록
• 답변
• 글쓰기
• 게시판 리스트 옵션
  • 수정
  • 삭제

Content material-addressable memory (CAM) is a particular type of computer memory utilized in certain very-excessive-velocity looking applications. It is often known as associative memory or associative storage and compares input search knowledge in opposition to a table of saved knowledge, and returns the deal with of matching information. CAM is often utilized in networking gadgets the place it quickens forwarding data base and routing table operations. This type of associative memory can also be used in cache memory. In associative cache memory, both address and content is saved aspect by side. When the handle matches, the corresponding content is fetched from cache memory. Dudley Allen Buck invented the idea of content material-addressable memory in 1955. Buck is credited with the thought of recognition unit. Not like standard laptop memory, random-entry memory (RAM), through which the consumer supplies a memory tackle and the RAM returns the info phrase stored at that handle, a CAM is designed such that the person provides a knowledge phrase and the CAM searches its total memory to see if that knowledge phrase is saved wherever in it.

If the data word is discovered, the CAM returns an inventory of a number of storage addresses the place the word was found. Thus, a CAM is the hardware embodiment of what in software program terms would be called an associative array. A significant interface definition for CAMs and different community search engines like google was specified in an interoperability agreement called the Look-Apart Interface (LA-1 and LA-1B) developed by the Community Processing Discussion board. Numerous units conforming to the interoperability agreement have been produced by Built-in Machine Expertise, Cypress Semiconductor, IBM, Broadcom and others. On December 11, 2007, the OIF printed the serial look-aside (SLA) interface settlement. CAM is much faster than RAM in knowledge search functions. There are cost disadvantages to CAM, nevertheless. In contrast to a RAM chip, which has easy storage cells, each particular person memory bit in a fully parallel CAM will need to have its own related comparison circuit to detect a match between the saved bit and the enter bit. Moreover, match outputs from every cell in the data phrase should be combined to yield a whole information word match sign.

The extra circuitry will increase the physical dimension and manufacturing cost of the CAM chip. The additional circuitry also will increase energy dissipation since each comparability circuit is active on every clock cycle. Consequently, CAM is used only in specialized applications where searching velocity cannot be accomplished utilizing a less pricey methodology. One profitable early implementation was a Common Purpose Associative Processor IC and System. MOSAID introduced CAM merchandise focusing on networking purposes. These merchandise were labelled Network Engines like google (NSE), Community Search Accelerators (NSA), and Knowledge-primarily based Processors (KBP) however had been primarily CAM with specialised interfaces and features optimized for networking. Presently Broadcom offers a number of households of KBPs. To achieve a special steadiness between speed, memory measurement and cost, some implementations emulate the function of CAM by utilizing customary tree search or hashing designs in hardware, utilizing hardware tips like replication or pipelining to speed up efficient efficiency. These designs are often utilized in routers. The Luleå algorithm is an environment friendly implementation for longest prefix match searches as required in web routing tables.

X or don't care for a number of bits within the saved word, thus adding flexibility to the search. For instance, a saved phrase of 10XX0 in a ternary CAM will match any of the 4 search phrases 10000, 10010, 10100, Memory Wave memory booster or 10110. The added search flexibility comes at an additional value over binary CAM as the inner Memory Wave memory booster cell should now encode three attainable states as a substitute of the 2 for the binary CAM. This extra state is typically carried out by adding a mask bit (care or don't care bit) to every memory cell. In 2013, IBM fabricated a nonvolatile TCAM utilizing 2-transistor/2-resistive-storage (2T-2R) cells. A design of TCAM using hybrid Ferroelectric FeFET was just lately revealed by a bunch of Worldwide scientists. Content-addressable memory is often utilized in laptop networking gadgets. For instance, when a network swap receives a data frame from considered one of its ports, it updates an internal table with the frame's source MAC handle and the port it was acquired on.