The internal 3.5" racks are secured via a pair of metal bars which slide to lock/unlock the cage. I found this to be very convenient. Unlike most new cases which utilize a spring loading mechanism (such as the Fong Kai FK-320) Antec chose to go for a different and sturdier approach. Basically there are two bumps, sliding over the first one unlocks the cage and lets the user remove it while sliding it back reverses the process.
FULL STORY @ MIKHAILTECH (http://www.mikhailtech.com/articles/cases/sx1240/)