What is difference between extt2, ext3 and ext4 file-system ?

ext2 File System
1. No Journaling Support
2. Less Speed
3. Less Secure


ext3 File System
1. Journaling Support
2. More Speed
3. More Secure  

The main benefits that ext4 has over ext3 are: 

1- faster time stamping
2- faster file system checking
3- journaling checksums
4- extents (basically automatic space allocation to avoid fragmentation)