bought a used dell pc 2 years ago. cd-rom drive isn't working. want to replace with a basic unit. can i assume that my drive has an IDE interface? what does 16X or 52X mean? thanks.

Almost certainly IDE. 16x, 52x refer to the speed of the CD drive in reading or writing the data - original CD Roms could be considered 1x speed - over time their speed has increased and the figures you are quoting are a comparison with the early models.

Yes, you can assume the drive is IDE connected - almost all internal modern optical drives are. As long as the existing drive doesn't have an oddball front on it (not flat, or the front is missing and is part of the case), you should be able to replace it with any IDE connected CD or DVD drive. All modern optical drives have a motor that is capable of spinning at variable speeds. The 52X or whatever rating is a maximum CDRom CD read speed relative to the speed originally specified for playing standard audio CDs - most of the time the drive isn't actually spinning that fast. E.g. When you play a standard audio CD the drive is in 1x mode; when you have a data CD in the drive it may access it at the maximum speed part of the time. You might want to consider getting a combo CDrom reader/DVD reader drive, or a CD burner(and reader)drive, or a combo CD burner (and reader)/DVD reader drive, or a DVD/CD burner (reads both CDs and DVDs) - they are all only a bit more money these days. CD/DVD drives are only warrantied for 1 year. A tip for you. Windows will spin your CD or DVD drive frequently if it has a disk in it, even if you are not presently accessing it, sometimes at a lower speed without lighting up the activity led on the front of the drive. The bearings in the drive motor have a finite life and when they get too worn the drive can no longer spin as it should - that is usually the reason your drive stops working properly. If you want your drive to last longer, remove the CD or DVD disks when you aren't going to be using them.

Note that speed indicator for CDs and DVDs are different. 4X for a CD is much slower than 4X for a DVD. Do yourself a favor BACKUP!