A servo is a small piece of electronic equiptment that responds to a signal. When they do receive that signal, they move. In this case, the servo pushes the eject mechanism, which basically does the job of manual eject. If it is broken, it will not be pressing the mechanism, ergo not ejecting electronically.
Impact has your DVD Burner, but it is costly.
http://www.impactcomputers.com/t3013.html
There are other drives like CD-ROM, DVD-ROM, CD-RW/DVD-ROM, and DVD+RW drives. The DVD+/-RW is the most expensive.
Those are here:
http://www.impactcomputers.com/dellp...s-storage.html