The datails of I-94 are here:

http://www.amcits.com/i-94.asp

Note:

The purpose of the I-94 is only to show that you did depart the U.S. within the time allowed. If your I-94 is for A, G, H, F or J visa status, the airlines will often advise you to retain the I-94 and re-use it after your brief stay abroad. This is not a cause for concern and it is fairly common for persons in those categories to be advised to retain their original I-94's.