CAM/RAM switch memory

Question

Someone could explain to me the following statement, just read in Cisco Press ?

• CAM is significantly faster than RAM, as it searches the entire memory content in one cycle, instead of a single address at a time.

Answer 1

Using standard RAM with traditional data structure of lookup tables, it will take multiple lookups to find exactly what you want. This will burn CPU cycles as you walk the data structure.

CAM is Content Addressable Memory. That means you can present the CAM with what you want, and it will return the address in a single CPU cycle.

The best example of this is when a switch needs to find a destination MAC address in a table in order to find the switch interface where the MAC address was last seen. Even assuming the table was stored in order, with traditional DRAM, it could take many CPU cycles to find the MAC address in the table. With CAM, you simply present the CAM with the MAC address, and it will return the location of the information, and that happens in one CPU cycle.

The downside is that CAM is physically larger, much more expensive, and more power hungry than DRAM.

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