Note the difference between a drive and a driver: a drive is a mechanical device that spins disks; a driver is a software program that tells the computer how to use the drive (or other hardware). CD-ROM drivers are the most common, and lately I've been reminded that they can be a source of confusion for many people.
The first thing you should know is that CD drivers come in pairs: a vendor-specific driver provided by the CD drive manufacturer, and a common driver provided by Microsoft. The vendor-specific driver can take on many forms. You will have to read your CD documentation to find out the exact name and syntax, but the line that loads this driver is almost always found in the file C:\CONFIG.SYS. Some typical examples are:
DEVICE=C:\CDROM\CDMKE.SYS /D:MSCD000 /P:340 DEVICE=C:\PLEXTOR\PLEXTOR.SYS /D:PLEX0001 DEVICE=C:\GSCD\GSCDROM.SYS /D:MSCD0001 DEVICE=C:\DRIVERS\NEC_IDE.SYS /D:MSCD001
The second driver is MSCDEX.EXE, and it is loaded from the file C:\AUTOEXEC.BAT. Again, the exact line for your system may vary, but it will look something like this:
C:\DOS\MSCDEX.EXE /D:MSCD0001
If you paid really close attention, you may have noticed that all these lines have one thing in common: the "/D:". This is the really important bit, because it tells MSCDEX how to find the vendor-specific driver. As yyou can see from the sample CONFIG.SYS lines, it doesn't matter what the name is that follows /D:; but if is not exactly the same on both lines, the drivers will not work. (Be especially careful not to confuse 0's with O's; a lot of people trip up on that!)
For users of Windows 95, the issue of drivers is a little more detailed, but really no more difficult. First of all, if you're going to be using the CD-ROM in programs that run in DOS Mode, everything in the above section still applies to you with the following exceptions. First, MSCDEX.EXE has moved to a different directory:
C:\WINDOWS\COMMAND\MSCDEX.EXE /D:MSCD0001
Second, when you install Windows 95 it disables this line in your AUTOEXEC.BAT file and adds it to a file called C:\WINDOWS\DOSSTART.BAT. This means that MSCDEX is not loaded before Windows starts, because Windows 95 doesn't need it. When you shut down Windows and go into DOS Mode, it runs DOSSTART.BAT and loads MSCDEX then. This is fine if you always go to Windows first before going to DOS Mode, but if you boot directly to DOS Mode without going to Windows then you will have to reenable this line in your AUTOEXEC.BAT file. This can be done by simply changing the line:
REM - by Windows Setup - C:\WINDOWS\COMMAND\MSCDEX.EXE /D:MSCD0001
to:
C:\WINDOWS\COMMAND\MSCDEX.EXE /D:MSCD0001
just like it was to begin with.
If you aren't able to use the CD-ROM in Windows 95, then you have a completely different set of drivers to deal with. First of all, check whether the DOS drivers are loading before Windows. You can do this by pressing the [F8] key right when your computer says "Starting Windows 95" and choosing the "Step by step confirmation" option. If they both are, make a note of which drive letter is assigned to the CD (typically D:, but systems will vary.) Then go to the Control Panel, open the System icon, go to Device Manager, and see if your CD drive is listed. If it is, double-click on it, click on the Settings tab, and check the drive letters. If they are not the same as what MSCDEX used, that could be your problem. Just make both the start and end letters the same.
If your CD drive is not listed in Device Manager, check to see if your controller is working properly. This may be either a specific CD-ROM controller, the IDE hard disk controller, or a SCSI device controller. If you aren't using the DOS drivers and you can't get the Windows 95 drivers to work, you may have to install the DOS drivers at least temporarily until you can get Windows straightened out.