How to Detect a DoubleSpace Drive from a Batch File

• Whether DoubleSpace is loaded in memory -and-
  
  
• Whether a specified drive is a DoubleSpace-compressed drive

   Results                         Errorlevel
   ------------------------------------------

   DoubleSpace compressed drive         1
   DBLSPACE.BIN is not loaded           0
   Invalid drive                        0
   Other errors                         0
				

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Creating ISDBL.COM

1. Create a text file called C:\ISDBL.SRC using a text editor (such as Windows Notepad or MS-DOS Editor). This is the Debug script file. C:\ISDBL.SRC should contain the following lines exactly as they appear.
   
   NOTE: Press the ENTER key at the end of each line below.

         A 100
         MOV AX,2901
         MOV SI,81
         MOV DI,012D
   
         INT 21
         MOV DL,[012D]
         DEC DL
         JGE 0119
         MOV AH,19
         INT 21
         MOV DL,AL
         MOV AX,4A11
         MOV BX,1
         INT 2F
         MOV AX,4C00
         AND BL,80
         JZ 012B
         INC AL
         INT 21
   
         RCX
         AE
         N ISDBL.COM
         W
         Q
   						

   NOTE: You MUST press the ENTER key twice after the last "INT 21" line and once after the "Q" at the end of the Debug script.
2. From the MS-DOS command prompt on drive C, enter the following command to create the ISDBL.COM program:

         DEBUG < ISDBL.SRC
   						

   Debug reads and follows the instructions in the ISDBL.SRC file. It is recommended that you do not use this command from within Windows or when other programs are running. If ISDBL.SRC contains an error, Debug probably is not told when to quit; therefore, you will have to restart your system. Debug may even be instructed to cause your system to stop responding (hang). If this happens, restart your system and examine ISDBL.SRC for accuracy.
   
   If there are no errors in ISDBL.SCR, a few screens of information are displayed, ending with
   <nnnn>:012B INT 21
   <nnnn>:012D
   -RCX
   CX 0000
   :AE
   -N ISDBL.COM
   -W
   Writing 000AE bytes
   -Q
   where <nnnn> is a combination of letters and numbers, the exact combination of which varies. The remaining information should be exactly as above if ISDBL.COM was compiled correctly.
   
   Debug places the ISDBL.COM file in the current directory, which in the example above is C:\. It should be 174 bytes in size.

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Using ISDBL.COM

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DBLTEST.BAT

   @ECHO OFF
   REM This batch file uses ISDB.COM to test a drive to see if it
   REM was compressed with DoubleSpace.
   REM
   REM DBLTEST.BAT assumes that ISDBL.COM in in the current
   REM directory or a directory on the MS-DOS Path.
   REM
   REM The syntax for running this batch file is:
   REM    DBLTEST <drive>:
   REM
   REM where <drive>: is the name of the drive to test, for example C:
   REM If no drive is specified, the current drive is tested.
   REM
   ISDBL %1
   IF NOT ERRORLEVEL 1 GOTO FAILURE
   ECHO The drive %1 is a DoubleSpace compressed drive.
   GOTO END
   :FAILURE
   ECHO The drive %1 is not a DoubleSpace compressed drive.
   :END
				

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How ISDBL Works

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