Memory device search system and method

Abstract

A search system and method is provided that may implemented in a content addressable memory (CAM) using various different memory technologies including SRAMs. DRAMs or Embedded DRAMs. The search system increases the density and efficiency of the CAM by using a search tree to reduce the total number of entries that must be matched against the key.

Description

[0001] This invention relates generally to a system and method for performing rapid searches in a memory and in particular to a searching method and system for a content addressable memory device that permits rapid searches to be performed for data contained in the memory.[0002] A content addressable memory (CAM) device is a memory storage device that accelerates any application that requires fast searches of data stored in the memory. For example, searching a database, a list, or for a particular pattern in database machines, image or voice recognition or computer and communication networks may be particularly well suited to using a CAM. A CAM operates by simultaneously comparing the desired information provided by the user against a list of pre-stored entries. The CAM gives an order of magnitude reduction in search time as compared to a typical random access memory (RAM).[0003] A RAM is an integrated circuit that temporarily stores data. The data is stored in various different sto...

AI Technical Summary

Benefits of technology

0063] All of the preceding discussion about mapping are aimed at optimally avoiding the case where the entry forces all bins between the target bin and a bin with an available location to re-organize their least & most entry pointers. If that occurs at the same time that a new entry write attempt to the same bin occurs, that will cause a stall of the insertion process. This stall situation can not be avoided by any insertion algorithm if the CAM area is run continually in an "almost full" state. However, the "fullness" that causes the increase in the insertion times occurs at a much higher level than software hashing algorithms in the literature due to the ability to use the local compare and match logic for each bank to "invisibly" move entries transparently to the match & insertion process. It is important to note that this problem may be avoided since the user of the CAM may simply not operate the CAM area in an "almost full" state, or if that is unacceptable, sufficient "invisible memory" can be added to allow "buffer bins" to be mapped in to handle overflow situations. This mapping is the intended use of the indirection in the tree. Instead of moving entries out of a bin in bulk, with the required updates of APL pointers, a new bin can be selected by the 20 bit 2.sup.nd level SRAM pointer, and a bin of memory that has been held in reserve can be mapped "in between" existing bins in an area of the tree that is congested. This is a unique advantage of the invention, since table management in traditional cams, especially ternary cams that use the cam address as a match priority, can be very onerous. The invention allows easy and flexible allocation of leaf bins according to need.

0064] The invention allows for an extension to find set intersection of sets. If a datum belongs to several larger databases, the same data (masked or not) may be stored in several different addresses (i.e., with several different associations), however all the entries will be grouped together in the same or contiguous bins. Then, when a CAM operation (data search) takes place, all of the different data bases that contain that datum can be identified quickly, as they will all return match. This feature is a very important feature which can implement set intersection calculations for data bases that are resident in the CAM. For example, say that the data base for "U.S. cities" and the data base for "animals" are both resident in the CAM. When the data record "buffalo" is presented to the CAM,

Problems solved by technology

The key problems with typical CAMs is that compare logic, that performs the comparison of the desired data to each memory location in the CAM, must be located at every memory cell location which significantly increases the number of transistors that must be dedicated to the compare logic and correspondingly decreases the amount of storage the CAM (since fewer transistors may be used for stora

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