MSCDEX or Microsoft CD-ROM Extensions is a software program produced by Microsoft and included with MS-DOS 6.x and certain versions of Microsoft Windows. Earlier versions of MSCDEX since 1986 were installable add-ons for MS-DOS 3.1 and higher.
It is a driver executable which allows DOS programs to recognize, read, and control CD-ROMs using the High Sierra and - since version 2.0 as of 1988 - also the ISO 9660 file systems. This requires the previous loading of an appropriate CD-ROM device driver (example: OAKCDROM.SYS), usually from CONFIG.SYS.
The final version of the MSCDEX program was 2.96, included with Windows 95 and used when creating bootable floppy disks with CD-ROM support. Starting with Windows 95, CD-ROM access became possible through a 32-bit CDFS driver.
The driver uses the Microsoft Networks interface in MS-DOS. This is the reason that at least version 3.1 of MS-DOS is required. The driver essentially looks like a network drive from the system perspective. It's implemented as a TSR program and an extension to the redirector interface (CDEX).
Novell DOS 7, Caldera OpenDOS 7.01 and DR-DOS 7.02 and higher provide a functional equivalent to MSCDEX named NWCDEX, which also runs under MS-DOS and PC DOS. It has more flexible load-high capabilities, also allowing to relocate and run in protected mode through DPMS on 286 and higher processors, thereby leaving only a 7 KB stub in conventional or upper memory (in comparison to MSCDEX, which occupies some 16 KB). Using EMS with a page frame, NWCDEX can reduce its footprint even down to a few bytes in conventional memory. In contrast to MSCDEX, the driver does not depend on undocumented DOS APIs and therefore, with a third-party helper tool named INSTCDEX, can be loaded via INSTALL statements and be fully functional in CONFIG.SYS to increase chances to load the driver high and, under these operating systems, allow to load other drivers not only from hard disk but also from CD-ROM while the operating system is still processing CONFIG.SYS.
In 1998 Caldera provided a DRFAT32 driver for DR-DOS to dynamically mount and unmount FAT32 volumes on DOS versions otherwise not natively supporting FAT32. DRFAT32 uses a variation and extension of the CDEX API in order to achieve this and work with older DOS versions.
- History of Microsoft MS-DOS CD-ROM Extensions
- Barney, Douglas (1986-09-22). "Microsoft lets micros read CD-ROMs". Computerworld: 13. Retrieved 2016-11-18.
- Mace, Scott (1986-09-22). "Extensions to MS-DOS Run CD-ROM". InfoWorld. 8 (38): 1, 8. Retrieved 2016-11-09.
- Johnston, Stuart J. (1988-03-07). "Microsoft Steals Show At Its CD ROM Meeting - Firm Unveils Two Business Titles". InfoWorld: 198.
- Apparently release notes for Microsoft MS-DOS CD-ROM Extensions 2.1[permanent dead link]
- cybermax.tripod.com - Subject: Microsoft MS-DOS CD-ROM Extensions 2.1
- Paul, Matthias (1997-07-30) . NWDOS-TIPs — Tips & Tricks rund um Novell DOS 7, mit Blick auf undokumentierte Details, Bugs und Workarounds (e-book). MPDOSTIP (in German) (3, release 157 ed.). Archived from the original on 2016-11-04. Retrieved 2014-08-06. NWDOSTIP.TXT is a comprehensive work on Novell DOS 7 and OpenDOS 7.01, including the description of many undocumented features and internals. It is part of the author's yet larger MPDOSTIP.ZIP collection maintained up to 2001 and distributed on many sites at the time. The provided link points to a HTML-converted older version of the NWDOSTIP.TXT file.
- Schulman, Andrew; Brown, Ralf D.; Maxey, David; Michels, Raymond J.; Kyle, Jim (1994). Undocumented DOS - A programmer's guide to reserved MS-DOS functions and data structures - expanded to include MS-DOS 6, Novell DOS and Windows 3.1 (2 ed.). Addison Wesley. ISBN 978-0-201-63287-3.
- tmfc.net - SHSUCDX V3.03E CD-ROM Redirector
- About CorelCDX Version 1.0, archived from the original on 2016-11-18, retrieved 2016-11-18