The difference between synchronous and asynchronous

Answer one:
1. Asynchronous transfer

Typically, an asynchronous transfer is a transmission unit, with each character appended with a 1-bit starting bit and a 1-bit stop bit to mark the start and end of a character and to synchronize the data transfer in this implementation. The so-called asynchronous transfer refers to the time interval between a character and a character (beginning with the end of a character to the next character) that is variable, and does not need to strictly limit their time relationship. The starting bit corresponds to the binary value 0, which is expressed as a low level and occupies a 1-bit width. The stop bit corresponds to a binary value of 1, expressed as a high level, occupying a bit width. A character occupies the 5~8 bit, depending on the character set used by the data. For example, the Telegraph code character is 5 bits, the ASCII character is 7 bits, the Chinese character code is 8 bits. Additionally, a 1-bit parity bit is attached, and you can choose odd or even parity to implement simple error control for the character. In addition to the same data format (the number of bits of the character, the number of bits in the stop bit, the check digit and the check mode, etc.), the transmitting end and the receiving end should adopt the same transmission rate. Typical rates are: 9 b/S, 19.2kb/s, 56kb/s and so on.

Asynchronous transmission, also known as the end-to-end asynchronous communication, has the advantage of being simple and reliable and suitable for character-oriented and low-speed asynchronous communication situations. For example, the communication between a computer and a modem is this way. Its disadvantage is that the communication overhead, each transmission of a character to be additional two or three bits, communication efficiency is low. For example, when using a modem to surf the Internet, the general sense of speed is very slow, in addition to low transmission rate, and communication overhead, low communication efficiency is closely related.


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2. Synchronous transmission

Typically, a synchronous transfer is a data block as a transmission unit. The head and tail of each block are appended with a special character or sequence of bits, marking the beginning and end of a block of data, and typically attaching a checksum sequence (such as a 16-bit or 32-bit CRC checksum) to control the data block in error. The so-called synchronous transmission refers to the time interval between the data block and the data block is fixed, and must strictly stipulate their time relationship.

Answer two:
Please tell me some details, I am more mentally retarded, thank you
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Synchronization is blocking mode, asynchronous non-blocking mode.
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My understanding: Synchronization refers to the two-thread run being related, where one of the threads is blocking waiting for another thread to run. Async means that two threads are irrelevant and run their own.

Don't know right or wrong? Downstairs.
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Synchronization means that after the sender sends out the data, the receiver sends back the response before sending the next packet to the communication mode.
Asynchronous means that after the sender sends out the data, the receiver sends back the response, and then the next packet is communicated.

CSDN has been discussed on:
http://expert.csdn.net/Expert/topic/2646/2646592.xml?temp=.3842584
http://expert.csdn.net/Expert/topic/2659/2659726.xml?temp=.1480219
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To cite a less appropriate example, like this:
SendMessage (...)
TRACE0 ("Just like Send");

PostMessage (...)
TRACE0 ("Just like WSASend using overlapped");

SendMessage is called when the call does not return, and so on after the message response to execute TRACE0, which is synchronization.
PostMessage is returned immediately after the call and executes TRACE0 without a message response, which is asynchronous.

Answer three:

The difference between synchronous and asynchronous

For example: Ordinary B/s mode (synchronous) Ajax Technology (asynchronous)
Synchronization: Submit request, wait for server processing, processing completed returns this period the client browser cannot do anything
Asynchronous: Requests are processed through event triggering server processing (which is still something the browser can do)
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Synchronization is when you ask me to eat, I hear you go to dinner, if not heard, you keep barking until I tell you to hear, to go to dinner together.
Async is you call me, and then go to dinner, I can get the news immediately, may wait until after work to eat.

So, if I ask you to eat in a synchronized way, ask me to eat with the Async method, so you can save money.
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For example, a synchronous message is asynchronous when you call

Differences between synchronous and asynchronous (go)