Q. Block diagram of an associative memory?

The block diagram of an associative memory is displayed in Figure below. It comprises of a memory array and logic for m words with n bits per word. Argument register A and key register K both have n bits, one for every bit of a word. Match register M has m bits, one for each memory word. Every word in memory is compared in parallel with content of argument register then the words which match the bits of argument register set a corresponding bit in match register. After matching process those bits in match register which have been set denote the fact that their corresponding words have been matched. Reading is achieved by a sequential access to memory for those words whose corresponding bits in match register have been set.

Key register offers a mask for choosing a specific key or field in argument word. The complete argument is compared with every memory word if key register contains all 1s. Or else only those bits in argument which have 1s in their corresponding positions of key register are compared. So the key offers a mask or identifying information that specifies how reference to memory is made.

Figure: Associative Memory - Block Diagram

To explain with a numerical illustration assume that argument register A and key register K have the bit configuration displayed below. Only three leftmost bits of a compared with memory words since K has 1's on these positions.

A                101 111100

K                111 000000

Word 1       100 111100      no match

Word 2       101 000001      match      

Word 2 matches unmasked argument field since the three leftmost bits of argument and word are equal.