Read/write cycle, orStorage cycle, means rightstorageMinimum time interval required for two consecutive access operations[1]。Because some memories need a certain recovery time after an access operation, the access cycle is usually greater than or equal to the access time.The read/write cycle is generally related to the type of memory and reflects the speed of memory to a certain extent.
Chinese name
Read write cycle
Foreign name
read write cycle
Discipline
computer
Definition
Minimum time interval between two consecutive access operations
The read/write cycle refers to the minimum time interval required for two consecutive memory access operations.The length of the read/write cycle is generally related to the hit rate.In computers, many applications are related to the read/write cycle, for example,Dynamic random access memoryThe data can only be kept for a short time.In order to maintain data, DRAM uses capacitance storage, so it must refresh every other time.The refresh mode of dynamic random access memory is related to the read/write cycle.
hit rate
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Hit rate: It can be simply defined as the probability of access in M1 memory, which is generally obtained by simulation experiment.Select a group of representative programs, count the number of accesses to M1 memory N1 and M2 memory N2 respectively during program execution, and then calculate the number of accesses into the following (3-1) relationship.
（3－1）
The access cycle of the entire storage system can be represented by the access cycles T1, T2 and hit rate H of M1 and M2:
T=H·T1+(1－H)·T2 （3－2）
When the hit ratio H → 1, T → T1, that is, the access cycle T of the storage system is close to the access cycle T1 of the faster M1 memory.
storage
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Memory ismodern information technology Memory device used to store information in.Its concept is very broad and has many levels. In a digital system, memory can be used as long as binary data can be saved;In integrated circuit, a circuit with storage function without physical form is also called memory, such as RAM, FIFO, etc;In the system, storage devices with physical form are also called memory, such as memory module, TF card, etc.All information in the computer, including the input raw datacomputer program, intermediate running results and final running results are saved in the memory.It is based oncontrollerStore and retrieve information at the specified location.With memory, the computer has memory function and can work normally.The memory in the computer can be divided into main memory (memory) andAuxiliary memory(External storage), also divided intoExternal memoryandInternal memoryThe classification method of.External storage is usually magnetic media or optical disks, which can store information for a long time.Memory refers to the storage part on the motherboard, which is used to store data and programs currently being executed, but only for temporary storage of programs and data. If the power is turned off or powered off, data will be lost.
Refresh mode of dynamic random access memory
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In essence, the process of refreshing is a regenerative process in which the original information is read out first, then the original information is formed by the refreshing amplifier and rewritten.Since the memory cells are accessed randomly, it is possible that some memory cells will not be accessed for a long time, and if there is no reading, there will be no rewriting, and their original information will inevitably disappear.Therefore, the method of regular refresh must be adopted. It stipulates that all basic circuits of dynamic RAM must be refreshed once within a certain time, usually 2ms, 4ms or 8ms, which is the refresh cycle.During the refresh cycle, the dedicated refresh circuit completes the line by line refresh of the basic unit circuit.There are three common refresh methods, one is centralized, the other is decentralized, and the third is asynchronous[2]。
Burst Refresh
Centralized refresh is to refresh all storage units row by row for a period of time in a specified refresh cycle. At this moment, read/write operations must be stopped.The disadvantage of this method is that there is a memory access "dead zone", which is unfavorable for high-speed and efficient computer systems.
Distributed Refresh
Decentralized refresh means that the refresh of each row of storage units is completed in each read/write cycle.The access cycle is divided into two segments, the first half is used for reading, writing or maintaining, and the second half is used for refreshing.This kind of refresh overcomes the "dead zone" defect of centralized refresh, but it cannot improve the working efficiency of the whole machine.In order to really improve the working efficiency of the whole machine, a combination of centralization and decentralization should be adopted to overcome the "dead zone" and make full use of the feature that the maximum refresh interval is 2ms.
Asynchronous Refresh
Asynchronous refresh mode is a combination of the first two modes.
