RAM versus CAM

Fifty years ago John von Neumann proposed the concept of the stored-program computer in which both instructions and data are confined within the boundaries of a storage device called memory. Today a computer architect is faced with a bewildering variety of memory-types to choose from when implementing this concept in the hardware. The most commonly used storage device is called random-access memory (RAM). That is, the process of locating a word within the storage array involves giving its address. The time needed to retrieve the word remains the same irrespective of the physical location of the word in the array. However, many data processing applications require searching items in some data structure, such as a table, stored in the memory. The established procedure to search a table is: 1) to store all the items where they can be accessed in sequence; 2) choose a sequence of addresses; 3) read the contents of memory at each address, and 4) compare the information read with the item being searched until a match occurs. This is exorbitantly time-consuming if the table is very large and/or the search algorithm is relatively inefficient. This time can be significantly reduced if the stored data can be identified for access by the content of the data itself rather than by an address. A memory unit accessed by content is called an associative memory or content addressable memory (CAM). This type of memory is accessed simultaneously and in parallel on the basis of the data content. This paper addresses the question: Is content addressability better than random-accessibility?.