Associative memory

Memory that is accessed according to the characteristics of given content rather than by address

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Associative memory It is a memory that is accessed according to the characteristics of a given content rather than by address.

Chinese name: Associative memory

Foreign name: Associative memory
Features: information processing function

catalog

four Application in paging system
five Bidirectional associative memory

six Bibliography

brief introduction

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Memory that is accessed according to the characteristics of a given content rather than by address. The characteristics of associative memory are: ① In addition to storage function, it also has information processing Function. It can search according to the characteristics of the content sent Storage unit 。② For each Storage unit The parallel search can significantly improve the search speed. These characteristics are similar to the "associative" function of the human brain, so they are called associative memory.^[1]

Stored in memory information It can be described by two parameters: address and numerical value (content). If two Storage unit If the content in is used for some operation and the result is stored in one of the cells, the memory accessed by address is more suitable. If you search based on certain content characteristics Storage unit , the result can be obtained faster by using associative memory. and storage space The usage of is relatively economical, and the cost of modifying records System overhead It is also small. Associative memory is used in large data base Real-time retrieval and update of, and General purpose computer Of Virtual Storage And control system.^[1]

form

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The figure shows the composition of associative memory. Every Storage unit Both contain circuits for storage, comparison, reading and writing, and control. The search variable is stored in the comparison number register Medium. shield register It is used to mask some contents of the comparison number register, while the unmasked part is sent to the associative memory as a lookup variable. When searching, each Storage unit Compare its contents with the sent lookup variable. If equal, respond register The corresponding bit in is set to 1. If not, set 0. In this way, the search results will be stored in the response register Medium. Satisfying the search requirements Storage unit It is called response unit. The search is performed in parallel, so there may be more than one response unit, which is called multiple responses. At this time, if you want to write information , the information can be sent to the comparison number first register , and then sent to Lenovo memory through cooperation with the mask register, and written to these response units in parallel. Sometimes it can be written according to the address of the unit information 。 To read information , these cells must be decomposed one by one to determine the address order for reading, which is called multiple response decomposition and is completed by the multiple response resolver. Word selection register Used to select the Storage unit , plays the role of inter word shielding. "Comparison" is the most basic logical operation of associative memory, which can complete a variety of comparison operations for a given search variable. For example: all, unequal; Less than, greater than; Not greater than, not less than; Only greater than, only less than; In section, out of section, maximum value, minimum value, etc. These operations can be realized through corresponding algorithms on the basis of full comparison, or in Storage unit Add the corresponding logic circuit to undertake.^[1]

Insufficient

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Although associative memory has strong functions, it contains many circuits, so its cost is very high. Computer systems are often configured with such memory in a small scale to improve the performance price ratio of the whole system.^[1]

Application in paging system

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In a paging system, the CPU accesses the memory twice every time it accesses a data (accessing the page table and the actual physical address). In order to improve the speed of address transformation, a special cache with parallel query capability, called "associative memory" or "fast table", is added to store the currently accessed page table entries.^[1]

Bidirectional associative memory

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In the bidirectional associative memory model, a set of finite vector pairs establish the bidirectional associative relationship by a linear operator, and this linear calculation is the connection weight matrix of a network. The weight matrix is determined by the least square method. A special type of Lyapunov matrix equation is derived from the solution of the weight matrix.^[1]

Bibliography

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Jin Lan, Wang Dingxing, Shen Meiming, Parallel Processing Computer Architecture, National Defense Industry Press, Beijing, 1982.^[1]

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