CentOS 7 systemd
So, I am taking CentOS 7 for a spin and the first thing I noticed was how much faster it boots. Low and behold, SysV has been replaced by systemd. There is a simplistic explanation of the differences in "Here We Go Again, Another Linux Init: Intro to systemd." In a nutshell, systemd uses sockets for checking of dependencies thus allowing multiple services to start simultaneously. With SysV, services where loaded one at a time based on a defined order like requiring networking to have started prior to starting SSHd.
Once you wrap your head around this, the second article, "Managing Services on Linux with systemd," describes basic usage. I found "An introduction to systemd for CentOS 7" and "Systemd" to be very helpful. The latter being the most technical and most important to administrators.