|Your computer bios will spin any optical drive that has a CD or DVD in it while booting, if not all the time, then when a CD drive is before a hard drive in the boot order in your bios Setup settings, even if it is not bootable, or it is but you choose not to boot it, although if you have more than one with a disk in it it may spin only one.|
This applies to Win 95 and up:
Windows will always spin your optical drive that has a CD or DVD in it when Windows first starts up, but what you may not have realized is it will also spin the drive at seemingly random times when you do certain things in Windows even if you're not trying to access the drive at the time, such as when you use My Computer or Windows Explorer, it does NOT always light the drive's led when it does, it does not always spin it at it's full speed when it does, and it may spin slowly for a long time after it spins faster.
Some of that you may have noticed - e.g. there is a short delay when you access My Computer or Windows Explorer when you access them, and when you choose to Browse your computer, if the CD or DVD was not spinning at the time - the delay is because the drive is spinning up - the rest I first found out about when I had the top cover off of a CD drive's case when the drive was still connected and had a CD in it.
If your optical drive is noisy that's easy to confirm - you can hear it even if it's led doesn't come on; otherwise you can confirm it was spinning by pressing it's eject button if it's led doesn't come on - if it doesn't eject right away, it was spinning - it had to stop spinning before it could eject.
Usually the thing that makes an optical drive fail first is the drive motor's sleeve bearings (I've never seen one or heard of one that has ball bearings) wear and deteriorate to the point the drive motor can no longer spin at it's max speed, and eventually the drive can't even spin at 1X speed or won't spin at all.
If you want the motor in the drive to last a lot longer, and because of that have a usable drive a lot longer, take out all CDs and DVDs when you're not using them.