History of Microsoft MS-DOS CD-ROM Extensions (MSCDEX)

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Changes from Version 2.1 to 2.2

• Approximately 12K of conventional memory is freed by moving the dynamic buffers to EMS (expanded memory specification) memory.
• SETUP.EXE now detects EMS memory and automatically uses the /E option for installation when EMS memory is available.
• A set "Owner ID" bit in the directory entry is now recognized.
• The expanded memory interface now avoids writing extraneous data into the expanded memory buffers of an application.
• Function request #8, Absolute Disk Read, no longer returns an error when 0 (zero) sectors are requested.
• The MS-DOS version 4.0 interface now returns the "Access denied" or "File Not Found" error message, as it should, when appropriate.
• The return value of the READ Device Status command now indicates whether reading of the R-W subchannels is supported. The corresponding description for obtaining the audio subchannel information has been expanded to cover the need for obtaining this information concurrently with audio data.

Changes from Version 2.2 to 2.21

• Version 2.21 corrects the problem that can occur when you use the /S switch to share a CD-ROM drive on a network and hang the computer.
• Version 2.21 changes the MS-DOS version check to allow MS-DOS version 5.0, so a SETVER entry is no longer needed.

Changes from Version 2.21 to 2.22

• MSCDEX now loads into UMA. If there is enough memory available, MSCDEX version 2.21 and earlier can load into upper memory. MSCDEX version 2.21 and earlier require the load size of MSCDEX (which varies for different configurations) plus 48K of memory to load. The extra 48K of memory is added to ensure there is enough memory to load COMMAND.COM.
  
  MSCDEX version 2.22 checks to see if the driver is being loaded above 640K. If it is, MSCDEX does not add 48K to the initialization load size because it does not need to be concerned with the transient portion of COMMAND.COM.
• MSCDEX is no longer version dependent. If you are using MS-DOS 5.0 or 6.0, earlier version of MSCDEX require that you use SETVER.EXE to tell MSCDEX the MS-DOS version is 4.0.
• The /V switch now reports accurate memory statistics. Earlier versions of MSCDEX were not accurate.

Changes from Version 2.22 to 2.23

• MSCDEX version 2.22 erroneously assumes that files in a directory on a CD-ROM are sorted (collated by ASCII code value). Performing a file search could result in missed files if the files on the CD-ROM are not sorted. MSCDEX version 2.23 does not assume that the files are sorted but instead searches the entire directory and does not return a "File not found" error message unless the file does not actually exist.
• MSCDEX version 2.23 allows files and directory names to begin with an exclamation point (!), allowing EISA configuration files to be shipped on CD-ROMs.