Synchronization difference (Synchronous) and asynchronous (Asynchronous) method
Before speaking, we first look "Computer Organization" for an example of synchronous and asynchronous:
Synchronous and asynchronous reading and writing literacy difference:
Simultaneous read-write: to read the case study
- A first processor clock cycle a memory address on the address bus, this process may involve a plurality of status bus. After the establishment of the address lines, the processor sends a signal.
- The processor read address signals in the second memory clock cycle, a memory module identification over the conveyor
- After a clock cycle, the module places the data on the data bus
- Cancel signal processor reads the data and read.
Asynchronous operation: to read the case study
- The processor and the data into the corresponding address line, after waiting for the establishment of the data, and these data together with the read command issued
- Memory address decoding, the data onto the address bus
- Wait until after the address channel is established, memory module ackownledged line (I do not know how to translate properly ...) notify the processor has finished loading the data
- master reads the data and the read signal to cancel
- 4 cause memory modules active data connection and cut off ackownledged line
- After ackownledged line cut off, master elimination of address information
A synchronization problem lies, "All Devices ON A Synchronous Bus are tied to
A Fixed Clock Rate, at The System CAN not the Take Advantage of in Advances in Device Performance", this Ye Hao understand, synchronous read memory requirements ready in one clock cycle data is also required CPU is ready to address line \ signal line logo in one clock cycle, but the CPU and memory speed is a big difference, of course, a clock cycle is already the smallest unit, but if we do a little slower devices , it has no way to catch this bus up so fast. And "With Asynchronous Timing, A Mixture of FAST and SLOW Devices, the using older
and newer Technology, A CAN Share Bus", to be understood that: Because of the asynchronous method is controlled by the signal does not depend on the clock, so that various devices It can run on a single bus.
Paste explain two other bloggers:
Synchronous and asynchronous usually used to describe a method call.
Once the synchronization method call, the caller must call the method returns to continue until the subsequent behavior.
Like an asynchronous method invocation messaging, once started, the method call returns immediately, the caller can continue the subsequent operations. And, usually asynchronous method in another thread, the "real" implementation of the. The whole process, not hinder the work of the caller.
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Original link: https://blog.csdn.net/wang704987562/article/details/79827609
Synchronization is performed sequentially whole process, when the various processes are executed, and returns the result. A linear embodiment is performed, the process execution can not cross. Generally used for relatively strong flow of the program, such as user login, you need to complete in order to verify the user login system.
Asynchronous is just send a command to call, the caller without waiting for the method to be called completely finished; but continue with the following procedure. Is a form of parallel processing without waiting for completion of execution of a program, may perform other tasks, such as all the data page data load process, and then display the page does not need to acquire the like.
Their difference lies in wait for a need, a need to wait, in some cases, we will give priority to the development of the project selection need not wait for the asynchronous interaction, such as logging can use asynchronous mode to save.
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Disclaimer: This article is the original article CSDN bloggers "shiyonghm", and follow CC 4.0 BY-SA copyright agreement, reproduced, please attach the original source link and this statement. .
Original link: https://blog.csdn.net/shiyong1949/article/details/80854656