Sarang,
Dr. House is correct. Typically there are three horn-loaded speakers behind the screen for left, center, and right channels and two large horn-loaded subwoofers.
Most theaters use a 5.1 configuration with the rows of surrounds (usually four on each side wall) for the two surround channels. Sometimes there are two additional rear surrounds on the back wall, but because the vast majority of commercial films are released in a 5.1-channel format, a 7.1-channel decoder is not used. That may have changed recently in some cinemas with the appearance of some dedicated 7.1-channel mixes.
Regards,
Alan
