Comp case DVD, CD adjustments

My Dell Dimension 4100 (bought in 2000) has a CD and a DVD trays on front of the case.
There is a small ‘thumbwheel’ located beneath each tray opening.
Located beside each thumbwheel is also a small round opening with an arrow cw / ccw, which apparently uses an inserted screwdriver. My question is, what are these controls used for?

My DVD tray will play a DVD or a CD, and it will burn a loaded DVD or CD onto a CD, but it will not respond to a blank DVD or CD, so I cannot write with the DVD.
My CD tray works ok.

Thanks for any help

Small thumbwheel is probably the drive volume control, for when listening to audio CDs with headphones plugged in.

The small hole is probably to release the tray if the mechanical opening fails. You just poke a piece of strong wire or thin screwdriver in, and gently push. The tray should then open a bit to allow you to pull it out.

Maybe you have a CD-RW/DVD-ROM drive which is why it won’t write to blank DVDs.

It is indeed a DVD-ROM (The brand appears to be ‘Compact Disc’).
Pardon the ignorance, but if it won’t recognize or write to a DVD, what do I need to use?
Thanks

To write to a DVD you’ll have to buy a DVD burner.

[quote=trailguy;2016460]It is indeed a DVD-ROM (The brand appears to be ‘Compact Disc’).
Pardon the ignorance, but if it won’t recognize or write to a DVD, what do I need to use?
Thanks[/quote]
Take a quick look here and you will see what most are using, anyone of these will be good for what you want to do.
http://club.cdfreaks.com/f61/top-5-optical-drives-january-march-2008-cast-your-vote-now-234126/

That is a useful table, but seeing as the OP’s computer is 8 years old he might need to avoid the SATA interface burners…