• Using disks
  
  The diskcomp command works only with floppy disks. You cannot use diskcomp with a hard disk. If you specify a hard disk drive for Drive1 or Drive2, diskcomp displays the following error message:
  
  

  Invalid drive specification
  Specified drive does not exist
  or is nonremovable
  

• Comparing disks
  
  If all tracks on the two disks being compared are the same, diskcomp displays the following message:
  
  

  Compare OK
  

  If the tracks are not the same, diskcomp displays a message similar to the following:
  
  

  Compare error on
  side 1, track 2
  

  When diskcomp completes the comparison, it displays the following message:
  
  

  Compare another diskette (Y/N)?
  

  If you press Y, diskcomp prompts you to insert the disk for the next comparison. If you press N, diskcomp stops the comparison.
  
  When diskcomp makes the comparison, it ignores a disk's volume number.
  
  
• Omitting drive parameters
  
  If you omit the Drive2 parameter, diskcomp uses the current drive for Drive2. If you omit both drive parameters, diskcomp uses the current drive for both. If the current drive is the same as Drive1, diskcomp prompts you to swap disks as necessary.
  
  
• Using one drive
  
  If you specify the same floppy disk drive for Drive1 and Drive2, diskcomp compares them by using one drive and prompts you to insert the disks as necessary. You might have to swap the disks more than once, depending on the capacity of the disks and the amount of available memory.
  
  
• Comparing different types of disks
  
  Diskcomp cannot compare a single-sided disk with a double-sided disk, nor a high-density disk with a double-density disk. If the disk in Drive1 is not of the same type as the disk in Drive2, diskcomp displays the following message:
  
  

  Drive types or diskette types not compatible
  

• Using diskcomp with networks and redirected drives
  
  Diskcomp does not work on a network drive or on a drive created by the subst command. If you attempt to use diskcomp with a drive of any of these types, diskcomp displays the following error message:
  
  

  Invalid drive specification
  

• Comparing an original disk with a copy
  
  When you use diskcomp with a disk that you made by using copy, diskcomp might display a message similar to the following:
  
  

  Compare error on 
  side 0, track 0
  

  This type of error can occur even if the files on the disks are identical. Although copy duplicates information, it does not necessarily place it in the same location on the destination disk.
  
  
• Understanding diskcomp exit codes
  
  The following table explains each exit code.
  
  

  Exit code	Description
  0	Disks are the same
  1	Differences were found
  3	Hard error occurred
  4	Initialization error occurred

  To process exit codes that are returned by diskcomp, you can use the ERRORLEVEL environment variable on the if command line in a batch program.
  
  

If your computer has only one floppy disk drive (for example, drive A), and you want to compare two disks, type:

diskcomp a: a:

Diskcomp prompts you to insert each disk, as needed.

The following example illustrates how to process a diskcomp exit code in a batch program that uses the ERRORLEVEL environment variable on the if command line:

rem Checkout.bat compares the disks in drive A and B 
echo off 
diskcomp a: b: 
if errorlevel 4 goto ini_error 
if errorlevel 3 goto hard_error 
if errorlevel 1 goto no_compare
if errorlevel 0 goto compare_ok 
:ini_error 
echo ERROR: Insufficient memory or command invalid 
goto exit 
:hard_error 
echo ERROR: An irrecoverable error occurred 
goto exit 
:break 
echo "You just pressed CTRL+C" to stop the comparison 
goto exit 
:no_compare 
echo Disks are not the same 
goto exit 
:compare_ok 
echo The comparison was successful; the disks are the same 
goto exit 
:exit