How IDE CD-ROM Drives Work

IDE is a universal format for disk drives including cd-rom drives that allow for standardization of components within your computer that interact with the various drives. An IDE drive is identified by a standard 40 pin socket and cable. Should your cd-rom drive contain a different pinning sequence than the standard IDE parameters or a different cable interface than the standard 40 pin then it is a proprietary system of the manufacturer and that manufacturer's recommended interface card and driver software must be used for the unit to function. For the purpose of this article we will deal with the IDE standard only.

IDE cd-rom drives are not native devices to your computer's BIOS such as the floppy and hard disk drives. Even though your BIOS may recognize the cd-rom on bootup, device drivers still have to be added to your system's hard drive with appropriate .sys files in your config.sys file and mscdex.exe* files in your autoexec.bat file.

As your computer boots the BIOS recognizes the various IDE drives then searchs for the startup files config.sys then autoexec.bat. Command lines are added to these files that invoke the appropriate .sys and mscdex.exe files through a pathway to these files. Without these files your cd-rom drive will not work or be recognized by your operating system as an available drive.

*Windows95 and Windows98 use their own mscdex.exe drivers and will remark your driver line in the autoexec.bat file so it will not be invoked. However, for the cd-rom drive to work in DOS-MODE for Windows95 you must have the driver line added to the DOSSTART.BAT file usally located in the Windows sub-directory.

SYS Files

Every IDE cd-rom drive has it's own .sys files or uses generic .sys files to setup the first part of the cd-rom drive interface to your operating system. They may be named differently but they all accomplish the same results. USDrives uses a usdrive.sys file, Cyberdrive uses a cybide.sys file while Mitsumi uses a more generic ide.sys file or a derivative of the ide.sys file.

If you have the drivers made specifically for your cd-rom drive it is always best to use them. If not you can use generic drivers from Mitsumi or Oak Technologies that works with around 90% of the IDE cd-rom drives on the market. Mitsumi provides a great tool with it's cd-rom drives called Disk Detective that identifys and installs your cd-rom drivers.

Below is a typical command line located in the config.sys file:

MSCDEX Files

MSCDEX.EXE is an excutable file that completes the operating system interface to the cd-rom drive so that the operating system may recognize the drive. This command line must be in the DOSSTART.BAT file in the Windows sub-directory for your cd-rom drive to work in MS-DOS mode in Windows95.

There are other switches for this command. Go to a DOS prompt such as C:\ and type HELP then press enter. You will find many DOS commands listed. MSCDEX should be near the bottom of the second column of commands. Highlight this command and press enter for more information on the various switches available with this command.

***NOTE***
In Window95 and Windows98 the autoexec.bat cd-rom command line will be modified as shown below:

rem - By Windows Setup - C:\WINDOWS\COMMAND\MSCDEX /V /D:CD003 /M:10

The rem command prevents the command line from being invoked as these operating systems establish there own mscdex drivers.

Summary

Your hard disk drive must be usable in that it must contain a formatted partition in order to copy files to the drive. Removing a partition or formatting a drive with data already on it will erase that data. You use the fdisk command in MS-DOS mode to view, erase or setup a partition. If you do not know how to do this, then go to your local dealer as this is important that it be setup properly. Caution---Use fdisk carefully as the wrong choices can erase your drive contents.

In order to setup a cd-rom in DOS you will need to:

1. create a subdirectory for the .sys file and the mscdex.exe file if they are not already on the drive.
2. modify the config.sys file to add a command line similar to that listed above
3. modify the autoexec.bat file to add a command line similar to that listed above

Make sure the pathways to the .sys and mscdex.exe are correct in the config.sys and autoexec.bat files or the drivers will not be found. If you have the installation disk that came with the cd-rom it should setup the files and subdirectory automatically.

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