"Mode" in this context refers to the design of your CD-ROM device driver. 16-bit real-mode drivers run in conventional memory and tend to be slower than their 32-bit protected-mode counterparts. To find out whether your CD-ROM is using a real-mode driver, check your config.sys file. A line similar to the following -- DEVICE=C:\CDMKE44.SYS /D:MSCD001 -- indicates that a real-mode CD-ROM device driver is being loaded.
In most cases, Windows 95 doesn?t require a real-mode CD-ROM driver, and you may find that config.sys references to the CD-ROM driver have been commented out (the word "REM" appears at the start of the line). This usually happens automatically when Win95 is installed. Even if a real-mode driver has been loaded from config.sys, Windows 95 will often disable it and replace it with a 32-bit driver during the startup process. This reclaims memory used by the real-mode driver and usually yields performance advantages.

If real-mode drivers are in use, they will be listed under Performance status

So why worry about real-mode drivers at all? Well, a small number of CD-ROM drives will not run under Windows 95 without real-mode drivers. These devices are discussed on the Web at http://www.microsoft.com/kb/articles/Q131/4/99.htm. But more importantly, protected-mode drivers are not available if you boot to a command prompt or restart your machine in MS-DOS mode. In these circumstances, real-mode drivers must be installed if the CD-ROM drive is to be accessible.
To find out whether a driver is running in real- or protected-mode, click the Performance tab of the System option in Control Panel. If all your drives are running in protected-mode, you will see the message: "Your system is configured for optimal performance." If real-mode drivers are in use, they will be listed under Performance status.
- Neville Clarkson