I dont know much about computer thing and just knew that mac has a built-in backup called time-machine? what is that? can it help us recover the lost data in my mac. and why people still need some third party mac data recovery tool like minitool mac data recovery software used by my friends for a couple of years?
Time Machine is a bit different from third party data recovery software. Here's how they work:
When your computer is connected to an external hard drive and Time Machine is turned on, every hour it backs up the files on your computer (or any files changed since the previous backup). In this way, you always have a copy of everything, including versions going back in the past (depending on how large the external hard drive is). Then if you lose a file, you can grab a copy from this backup. (As a side note, the latest version of OS X includes a Versions feature that makes locally stored backups of older versions of files, so if you change a document, you can still see what it used to be.)
Third party data recovery software, on the other hand, is what you use when you do not have an actual backup to rely on. It's also not very reliable. What this does is it tries to scan your Mac's hard drive's empty space for files that were deleted. This sometimes works because even though files are deleted from the hard drive, the hard drive isn't necessarily overwritten, so some deleted files may still be retrievable.
Time Machine is a tool by Apple that stores incremental backups to an external hard drive. Third party applications may add other functionality your friends may not want. From personal experience, Time Machine has saved me several times & I recommend it. For more info on Time Machine, see this article: http://support.apple.com/kb/HT1427
From time to time your hard disk might write garbage that results in corrupt files. Time Machine will have no clue that those files are corrupt and will back them up. Hopefully Time Machine will have backed up a good copy at some point in the past.
HFS+ is an old filesystem and doesn’t do much to prevent filesystem corruption. That’s when a data recovery tool might come in handy.