Filesystem:/System/Library/LaunchDaemons/com.apple.SpringBoard.plist

This file loads SpringBoard at boot and tells it to re-launch itself when killed (this is how re-springs are possible).

File Contents
The contents of this file on an iPod touch 2G running iOS 4.2.1 is as follows:  <!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">  EmbeddedPrivilegeDispensation KeepAlive Label com.apple.SpringBoard MachServices PurpleSystemEventPort ResetAtClose com.apple.CARenderServer ResetAtClose com.apple.SBUserNotification com.apple.UIKit.statusbarserver com.apple.iohideventsystem ResetAtClose com.apple.smsserver ResetAtClose com.apple.springboard ResetAtClose com.apple.springboard.UIKit.migserver ResetAtClose com.apple.springboard.alerts ResetAtClose com.apple.springboard.appstatechanged HideUntilCheckIn com.apple.springboard.backgroundappservices ResetAtClose com.apple.springboard.processassertionservices HideUntilCheckIn ResetAtClose com.apple.springboard.processinvalidation HideUntilCheckIn com.apple.springboard.remotenotifications ResetAtClose com.apple.springboard.services ResetAtClose com.apple.springboard.watchdogserver ProgramArguments /System/Library/CoreServices/SpringBoard.app/SpringBoard ThrottleInterval 5  UserName mobile

The contents in this file may vary slightly between iOS versions.