The voting works as follows:

All IOC members are entitled to vote - though Samaranch does not participate unless a casting vote is needed.

To win, a city needs to gain an absolute majority of votes which rarely happens on the first round.

After the first round, the city with the fewest votes is eliminated and IOC members are asked to vote again between the remaining four.

This process continues until one city wins an absolute majority or until only two candidates are left for a final round. At that stage, the city with the most votes wins - even if it does not have an absolute majority.

Samaranch, obviously, tells members after each round which city has been eliminated, but he gives no details of voting figures until the entire process is over and the new Olympic host has been declared.

If two cities are tied for the fewest number of votes in any round, an extra vote between the two is taken. The city with the lowest number of votes in this extra round is then eliminated.

The process can take some time and the IOC allows one-and-a-half hours to ensure Samaranch will have an envelope in his hand at 5.30 p.m. on Friday.