Rav vs. Rabbi in Talmudic Times

Question

I was reading about the life of Rabbi Zera, and it said he was originally a Rav. The Rabbis of Eretz Yisrael offered to confer on him the title of Rabbi and at first he refused, until they told of some special spirtual attributes he would gain and then he accepted.

So what was the difference in Talmudic times between a Rav and a Rabbi and what beneficial about the later?

Edit

Here is where I originally read about it in Wikipedia:

Ze'era was highly esteemed by Abbahu, the rector at Cæsarea, of whom he considered himself a pupil. He was ordained rabbi, a distinction usually denied to members of the Babylonian school, and though in the beginning he refused this honor (Yer. Bik. 65c), he later accepted it on learning of the atoning powers connected with the dignity (Sanh. 14a). Upon receiving Semicha, his title changed from Rav to Rabbi.

Answer 1

The term "rabbi" means that the person received semikha (not to be confused with the modern form of semikha which is different). There was no semikha in Bavel, so none of the amoraim who lived there were "rabbi" unless they came to Eretz Yisrael.

An easy way to remember this is by looking at the last letter of the word. "Rav" ends with ב which is also the first letter in Bavel. "Rabbi" ends with י which is also the first letter of Yisrael. This is also a useful way of figuring out whether a person quoted in the Talmud is a tanna or an amora. There were no tannaim in Bavel, so if you see "Rav" it must be an amora. There were some amoraim in Israel, though, so "rabbi" does not necessarily mean tanna. For example, Rabbi Yochanan is an amora from Israel.