About the USB flash drive / hard drive hot swap, you need to know two or three things

For many tails, may there be more or less the experience of pulling a USB disk or a hard disk? After losing the file, we will lose the U disk. After we have learned the lessons of countless blood, we have almost been taught the fixed process of "popping before pulling the disk". However, is it really only after the security pops up that you can pull the disk?

In fact, it is not necessary in normal terms, because our commonly used USB interface has a special hot plug design.

Support for hot swapping is a common design for mainstream interfaces. When the external bus standard of USB was introduced in 1994, the USB interface was considered to support hot plugging. The hot-swap design of the hardware layer of the USB-A interface is to use two of the four contacts of the USB male port as power supply contacts, and the inner two are used as data transmission contacts, and the length of the outer power supply contacts is designed. It is longer than the inner transmission contact.

The clever thing about this design is that when the USB external device is plugged in, the external power supply contacts are first connected to the motherboard to supply power to the device, and then the inner data transmission contact is connected and accepts the system command to transmit data; when the USB device is unplugged When it is out, the inner transmission contact is disengaged first, the data transmission is interrupted, and then the power supply contact is disengaged and the power supply to the external device is stopped. Although we plug and unplug the hard disk and the USB flash drive are only a momentary action, the USB "first power off and power off" design normally ensures that the external device will not be corrupted or hardware when the USB connection is forcibly disconnected. malfunction.

However, accidents are always there, and most of these "numbers of deaths" accidents occur when the U disk / hard disk handle is locked (that is, in the data transmission state) is forcibly disconnected. Pulling out the USB flash drive/hard disk in the data transfer state may cause the logical allocation table to be damaged (formatted) or the physical damage of the flash chip (discarded).

 Therefore, the pre-emptive condition for hot plugging is "ensure that the USB flash drive/hard disk is not occupied", and the "safe pop-up" function introduced by Windows is also to allow the user to manually confirm that the external storage device is idle before being ejected. When the user clicks on the security pop-up, the system will start to check whether the file transfer activity of the U disk/hard disk has stopped. If a process is occupying an external USB disk/hard disk transfer or index data, the system will reject the pop-up request.

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