Question

What is this LOST. DIR
It always comes even if I delete it
&it contains nothing.

Answer 1

The Lost.dir is a system folder. Its a place where the Android OS places files that were recovered during a system boot up (ie when you turn on your phone). It is analogous to the 'Recycle Bin' under Windows OS. The files which are stored inside this directory are often recoverable. Most of the times you won't find anything at all in LOST.DIR directory.

What files are stored in LOST.DIR ?

If you were saving files and suddenly the phone turned off, or maybe you pull the SD card out when files were being written to it - the Android system places copies of those files in LOST.DIR directory so it can try and recover them on the next boot (next time the system starts up). The files in the process of copying are also renamed. So if you find wierdely named files in the folder, don't be surprised as they are only renamed versions of erstwhile files present on your device.
 Files may end up stored in LOST.DIR folder due to following reasons :

Abruptly pulling out SD card from Android phone

Interruptions while downloading files on Android device

Sudden freezing of Android device operating system

Switching off the device while some read-write process is carrying on.

How do I recover files from LOST.DIR folder?

In order to stop permanent loss of files from LOST.DIR folder in Android, you have to quickly recover missing files before your Android smartphone memory space is overwritten by some new data. Therefore use of some pertinent LOST.DIR Android recovery tool is recommended. Yodot Android Data Recover, Recuva are a couple of examples which worked for me.

Can I delete the contents of LOST.DIR ?



In order to save precious memory space its completely normal to delete the contents of LOST.DIR as it only acts as a recycle bin. You can also delete the LOST.DIR folder itself but it will reappear the next time the system boots up. When your Android system throws up a message saying 'Preparing external SD card' its actually checking the contents of LOST.DIR, and if it fails to locate the directory, it creates one.

Necessary Guidelines :

Avoid abrupt removal of Android device's memory card while transferring data to/from the system.

Backup your images or other files to some other device.

Use authentic android antivirus software to protect yourself from virus-attack.

THIS IS MY BEST ADVICE
AND EXPLANATION