Your BCIS Arrival/Departure record, it is a small white card usually stapled to your passport. You receive this on the airplane before you enter the U.S.. BCIS will take one half, staple the other half to your passport and write "J-1 " and "D/S" on it.
I-94 is a white card issued to all nonimmigrants by the U.S. immigration inspectors at the port of entry. It is evidence of legal entry into the U.S., indicating date of entry, status granted (F-1 or J-1), and length of stay granted. Your I-94 card should have either F-1 or J-1, and D/S written on.
The small white card also known as the arrival/departure record. It is issued to the student at the port of entry by a DHS officer and removed from the passport when the student leaves the U.S. It is a very important document that verifies a nonimmigrant's legal entry to the U.S., including the date of arrival, the classification of the individual, and the time allowed to remain in the United States. It is the I-94 and not the visa stamp that controls how long someone may remain in the U.S. legally.