It's been 17 years since the federal government last faced a partial shutdown because Congress and the president couldn't agree on a spending bill. A lot has changed in that time, leaving federal employees, citizens and even government decision-makers confused about what a shutdown would mean.Every shutdown is different. The politics that cause them are different. Because of technology and structural overhauls, the way the government functions has changed since 1996. Much of what will happen is unknown.Here's what we do know about Tuesday's looming shutdown: