The Microsoft MS-DOS CD-ROM Extensions (MSCDEX) are an extension to the MS-DOS operating system which permit reading CD-ROM discs which conform to both the High Sierra May 28th format and the ISO-9660 version of the High Sierra format. The CD-ROM disc appears just like a magnetic disk to the user and to applications software, ensuring compatibility with current software.

This document looks at the MSCDEX interrupts provided by the driver and how to use them to interface with the CD-ROM drive.