Hello,
As others said there's nothing special about a 486DX and DOS CD-ROM. Maybe you were reading about specifications for a "Multimedia PC"
As standards to interface a CD-ROM to a computer were in flux when DOS (and Windows 3.x) were current, the driver is split into two parts:
1. A specific hardware driver for your CD-ROM interface goes into config.sys
2. A standard component called MSCDEX which ships with DOS 6.x goes into autoexec.bat. It assigns the drive a letter and translates between programs accessing that letter and the lower-level driver you put in config.sys.
If the drive is a standard IDE drive, from about 1995 onward, it's called ATAPI and oakcdrom.sys suggested by weedeewee will work.
If it's an older, proprietary interface that connects through your sound card, you may need a particular driver for your drive.
There was a boot disk back then called the "CD-ROM God" to help locate such a driver if you end up needing it.
Windows 3.x doesn't have any special protected-mode CD-ROM support. You just set up the CD-ROM in DOS and it goes through DOS to access it. You do want to make sure SMARTDRV is caching the CD-ROM. You do that by putting mscdex before smartdrv in your autoexec.bat.