TCAM and Cam

CAM is the abbreviation of content addressable memory, that is, the meaning of "contents addressed storage", it is the associative memory memory based on traditional storage technology, there are three basic operations about CAM:

1). Write operation: Enter the address and data, write the data to the specified address, the writing speed is the same as RAM;

2). Read operation: Enter the address, return the data on the address, the reading speed is the same as RAM;

3). Find operation: Enter unknown origin data to return the address where the data is stored. This is also the main use of CAM, it is able to quickly find from a huge database, and return the best matching address, the fastest search speed can reach more than 100 million times per second.

Tcam is the abbreviation of ternary content addressable memory, that is, the meaning of "three-state contents addressable memory", which is developed from Cam. In general cam memory, each bit state has only two, "0" or "1", and the Tcam each bit bit has three states, remove "0" and "1", there is a "t care" state, so called "three states", it is through the mask to achieve, It is this third State feature of Tcam that makes it possible to find both exact matches and fuzzy matches, while Cam does not have a third state, so it can only perform exact matching lookups.

In addition to the ASIC chip, the implementation of TCAM can also be implemented with IP cores on the FPGA.

Reference documents:

[1] Three-state content-addressable memory (TCAM) working principle. Http://blog.sina.com.cn/s/blog_b16cbfbd01018lzw.html

[2] TCAM. Baidu Encyclopedia.

[3] parameterizable content-addressable Memory. Xapp1151_param_cam.pdf

TCAM and Cam