KB101884 - How to Detect a DoubleSpace Drive from a Batch File

MORE INFORMATION

This following is an example of how to use the MS-DOS Debug utility to create a program file called ISDBL.COM. ISDBL.COM determines the following:

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

ISDBL.COM returns the following errorlevels:

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

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

NOTE: ISDBL.COM tests the current drive if no drive is specified on the command line.

Creating ISDBL.COM

ISDBL.COM is created using a Debug script file, which contains all the commands you would enter from within DEBUG to create ISDBL.COM.

To create ISDBL.COM, follow these steps exactly:

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.
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.

Using ISDBL.COM

You can now run the ISDBL.COM program from within a batch file to get information about a specific drive. Below is an example batch file:

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

How ISDBL Works

In determining whether the drive is compressed, ISDBL assumes that DoubleSpace is running.

ISDBL checks the specified drive by using Interrupt 2F, function 4A11. This function is the DSGetDriveMapping application programming interface (API) call for DoubleSpace. If the drive is compressed, then Bit 7 of BL will be set. Otherwise, it is zero. This result is simply returned at the end of ISDBL.

How to Detect a DoubleSpace Drive from a Batch File

SUMMARY