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

This is a file located in /System/Library/LaunchDaemons that loads SpringBoard at boot and tells it to re-launch itself when killed (This is how re-springs are possible). The contents of this file on an iPod Touch 2 running iOS 4.2.1 is as follows:

File Contents
 <!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 shouldn't change too much based on devices/iOS versions, but may vary slightly.

Important Notes
Whatever you do, stay away from this file. Messing with its contents will bring nothing but trouble. If you are feeling adventurous and tell SpringBoard to run as "root" instead of "mobile", your device will turn on, but you will be unable to open any apps. They will open their "loading.png" then immediately crash, probably because the sandbox doesn't want to run as root.

Parents
(Root)/System/Library/LaunchDaemons