Associative Memory Computer Organization and Architecture by admin - January 6, 2023January 7, 20230 Share on Facebook Share Send email Mail Print Print Table of Contents Associative MemoryDifference between main memory and associative or content addressable memoryOrganization of associative memoryMatch logic for each cell Match Logic: Associative Memory Unlike the main memory which is accessed using the contents address and in sequential method, the associative memory is accessed by contents and is also called as the content addressable memory. For writing a word in memory, unused space is found by memory and the word written their. Word is read from memory by matching the word or its part with the contents/word stored in memory. Difference between main memory and associative or content addressable memory Main Memory Associative or Content addressable memory Memory accessed by using address of contents/words Memory is accessed by matching contents with word stored in memory To store a word, we assign the address and write the word at that address To write a word, memory finds the empty space and writes it there. To read a word an address is assigned and then a read command given. To read operation is performed by matching the content with every word in the memory. It has address decoder It has a match logic This type of memory is Cheaper This memory is expensive It is slow Faster Employed in general purpose computers Employed in applications where search time very critical and may be very short Organization of associative memory This type of memory consists of argument register, key register, match register, and the memory array with match logic. Figure shows the organization of such memory. Figure : Associative memory organization Features: Each word in memory is compared with content of argument register in parallel The word that match the bits of argument register set a bit in match register Key register is used to mask or unmask the bits of the argument register for choosing the searching criteria whole or piece of argument register for match logic Example Register A 101 10101 Register K 101 00000 Word 1 in memory 100 10101 No match Word 2 in memory 101 10111 match Match logic for each cell Each bit of the memory word is matched with the corresponding bit of the argument register. Figure shows one cell of the memory and its match logic. A memory cell consist of a flip-flop for storing a bit, read/ write logic, a match logic as shown in figure. Operation: Write to memory cell : Provide the bit at the input Give Write command. Output of a cell (a FF) =Fij Figure : Match Logic single cell Match Logic: It consists of simple two bit comparator that compares Fij and Aj of the argument register. An XNOR acts as an equality logic and algebraically it is written as : Xj = Aj ꙩ Fij or (Aj.Fij + Aj’.Fij’) All the xj are then ANDed to get the Mi as: Mi = x1.x2.x3………..xn The key register bits Kj in the comparison logic is include as per the following algorithm Xj + Kj’ = xj if kj = 1 = 1 if kj = 0 This can be achieved by including an OR gate with xj and kj’ as inputs. Share on Facebook Share Send email Mail Print Print