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[ The PC Guide | Troubleshooting and Repair Guide | The Troubleshooting Expert | Troubleshooting Specific Components | Troubleshooting CD-ROM Drives | Configuration Problems ]

The MSCDEX program that I am running in DOS is producing error messages or hanging up

Explanation: You are running MSCDEX to set up the CD-ROM drive as a drive letter under DOS but it is either hanging the system or producing an error message.

Diagnosis: MSCDEX is the file system extension that allows you to use a CD-ROM drive as a regular driver letter under DOS or Windows. It should not be used when you are running Windows 95. It will fail to load usually when there is a configuration problem, or when it cannot see the CD-ROM driver in memory.


  • Make sure that the CD-ROM driver is loading. If it isn't loading then there may be a problem with the drive or its configuration. Look here to troubleshoot this. Without the CD-ROM loaded, MSCDEX will never work.
  • Make sure that the CD-ROM driver's command line and the MSCDEX command line have identical, matching "/D:<xxx>" parameters; otherwise MSCDEX won't be able to find the drive.
  • There are different versions of MSCDEX, as it has been updated over time. You may need a newer version than the one installed on your system. Watch out for outdated install disks that come with CD-ROM drives. Some of them contain positively ancient versions of MSCDEX. Microsoft's web site should have the latest version.
  • One tricky problem has to do with the availability of drive letters. MSCDEX must be able to find an available drive letter to set up the CD-ROM drive. If for some bizarre reason the letters are all used up (never seen this happen, though I've seen systems that went up to S:) then MSCDEX will fail. More common than a full system is the use of the LASTDRIVE command in the CONFIG.SYS file. If you see a command there that says "LASTDRIVE=x" where "x" is a drive letter, no drive letters will be assigned by DOS above that one. If you have two hard disk volumes and "LASTDRIVE=D" then MSCDEX will not be able to install the CD-ROM. Remove the LASTDRIVE command (or set it to "Z") to solve the problem and make your life a lot simpler.

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