CD ROM support in DOS

Most Operating Systems these days automatically install the necessary support for your CD ROM drive as part of the normal Operating System Install. This is not true for DOS as all command line (pre Windows 95) versions of this Operating System predate the CD ROM drive as a commonly installed device on your PC. To get support for your CD ROM drive on a computer running DOS (with or without Windows 3.1) or from a DOS system disk such as you might create under Windows 95, you need to manually install the support for the drive.

To install support for your CD ROM drive under DOS, you must first locate a 16 bit device driver that supports your CD ROM drive and copy it to the hard drive (or floppy drive) containing your operating system. You also need to locate a special program that comes with your DOS operating system. With MS-DOS this file is called mscdex.exe, other DOS operating systems may name the file slightly differently (eg. Novell DOS 7 calls the file nwcdex.exe). You then need to place one additional command line into each of the config.sys and autoexec.bat files so as to get the driver to load when the operating system is booted.

The exact command to place in the config.sys file depends on where you placed the device driver file and what the file is called. Assuming that the file is called cdrom.sys and you placed it on the c: drive in the cdrom directory then the command to put in the config.sys file would read as follows:

 device=c:\cdrom\cdrom.sys /d:mscd001 

If your file has a different name or you placed it elsewhere then just substitute the correct name and location for the ones I have shown.

You now need to locate the mscdex.exe program (or equivalent - depending on your operating system) so that you can reference it in the autoexec.bat file. Let's say that you found it in the windows directory on your c: drive. In this case the statement to add to your autoexec.bat would read:

 c:\windows\mscdex /d:mscd001 

If your DOS version calls the file something different or it is located in a different spot then just substitute the location and name as appropriate.

There is nothing special about the mscd001 referenced in these two commands. This is the value most commonly used but you can in fact use any name you like as long as the same name appears in both statements. This comes in useful if you have more than one CD ROM drive and are defining support for them.

There are other parameters that you can specify on each of these statements if you require them. If the computer is unable to determine an appropriate address and IRQ for the CD ROM then this may (depending on your driver) be able to be specified on the statement in the config.sys file using /P:xxx and /I:nn flags respectively. If the default number of buffers allocated to the CD ROM is too low then a higher number can be allocated using the /M:nn flag on the statement in the autoexec.bat file.


This article written by Stephen Chapman, Felgall Pty Ltd.

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