Many data Processing application Required The Search Of items in a table stored in memory. An assembler program searches the Symbol address table in order to extract symbol’s binary equivalent. An account number may be seached In a file to determine the holder’s name and account status. The established way to Search a Table is to store all items Where they can be address in sequence.The search procedure is a strategy For choosing a sequence of address , reading the content of memory at each address, And comparing The information read With the items Being Search until a match occurs.the number of accesses to Memory depends On the location of the Item and efficiency Of the seach algorithm. Many search algorithm has been developed to minimize The number of access while Searching for an item In a random or sequential access memory
The time Required to find an item store in memory can be reduced considerably if Stored data Can be identified for access by the content of the data itself rather than by an address . a memory unit access by Content is called an associative memory or Content addressable memory(CMA). This type of memory is access simultaneous and in parallel on the basic of data content rather than by specific address or location . When a word is written in an associative memory , no address is given. the memory is capable of finding an empty unused location to store the word. When are word is to be read from and associative memory, the content of the word , or part of the word , is specified. The memory locates all the words with match the specified content and marks them for reading.
Because of its organization , the associative memory is uniquely suited to do parallel searchd by data association . moreover , search can be done on an entire word or on a specific field within a word. An associative memory is more expensive than a random access memory because each cell must have storage capability as well as logic circuits for matching it content with an external argument. For this reason , associative memories are used in applications where the search time is very critical and must be very short.