Convert DoubleSpace to DriveSpace in MS-DOS 6.22

In MS-DOS 6.22, the utility used to convert DoubleSpace compressed drives to the DriveSpace format is DriveSpace itself, executed via the command DRVSPACE (or DRVSPACE.EXE). This utility replaced DoubleSpace following legal disputes and provides a built-in conversion process that migrates older Compressed Volume Files (CVFs) to the newer DriveSpace format without data loss.

Background: DoubleSpace to DriveSpace

Microsoft introduced DoubleSpace (DBLSPACE) in MS-DOS 6.0 and 6.2 to enable on-the-fly disk compression. Following a patent infringement lawsuit won by Stac Electronics, Microsoft released MS-DOS 6.21 with all compression software completely removed. Shortly thereafter, Microsoft released MS-DOS 6.22 featuring DriveSpace, an updated disk compression engine designed to replace DoubleSpace.

How the Conversion Process Works

When upgrading an existing system from MS-DOS 6.0 or 6.2 to version 6.22, the operating system retains the existing DoubleSpace files until the user initiates the conversion.

To convert DoubleSpace drives to DriveSpace:

  1. Run the Utility: At the MS-DOS prompt, enter DRVSPACE. Alternatively, entering DBLSPACE will automatically launch the DriveSpace executable, as MS-DOS 6.22 includes a stub redirecting legacy commands to DRVSPACE.EXE.
  2. Follow the On-Screen Prompts: DriveSpace automatically detects any existing DoubleSpace volumes (typically stored as hidden files named DBLSPACE.000, DBLSPACE.001, etc.).
  3. Confirm Conversion: The utility prompts you to convert the detected DoubleSpace drives to DriveSpace format. Once confirmed, the utility alters the internal compression headers and changes the underlying Compressed Volume Files to the DriveSpace naming standard (such as DRVSPACE.000).

System Configuration Updates

During the conversion, the utility updates the system boot files:

  • It updates the memory-resident device driver in CONFIG.SYS, changing references from DBLSPACE.SYS to DRVSPACE.SYS.
  • It updates the hidden boot driver files in the root directory, replacing DBLSPACE.BIN with DRVSPACE.BIN.

Once the conversion completes, the system reboots, and the drive operates entirely under the DriveSpace compression engine.