Slot payback percentages are not controlled by a central computer.

In order to change the payback percentage the chip must be changed in each machine.

There is, however, a new generation of machines being tested where the game itself (which would include the chip controlling the payback percentage) can be changed from a central computer.

According to Nevada gaming regulations, before making the change, the machine must be idle for four minutes and then a message must be displayed on the machine to notify the public that the game is being changed. After the change, the machine must again remain idle for four more minutes before being played.

These machines are being tested in some casinos around the country.

For more information on how slots work, listen to some podcasts on the following page:
http://www.americancasinoguide.com/podcasts.shtml