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 How To Have More than 15 Files Open in MS-DOS 3.3 and Later - Q31509
 
 To open more than 15 files at once in a program under Microsoft
 MS-DOS, you must do the following:
 
  - Use MS-DOS version 3.3 or later. (You can determine the
    MS-DOS version number with the VER command at the command prompt.)
 
  - Add the statement FILES=n to the CONFIG.SYS file.
 
  - Call MS-DOS Interrupt 21h with function 67h from the program, as
    shown in the example listed below.
 
  - If you are using the SHARE.EXE utility, you must also invoke
    SHARE/F:nnnnn to increase the area for file-sharing information
    above the default of 2048 bytes. See your MS-DOS manual for more
    information about the SHARE utility.
 
    The following is an example of using SHARE/F:
 
       share/f:16384
 
 More Information:
 
 This technique will retain the file handle table size across a CHAIN
 for programs compiled without the BC /O option. Programs that are
 compiled with the BC /O (stand-alone .EXE) option and CHAINed will
 revert to the original file handle table size.
 
 Please note that even if you follow the above steps and specify
 FILES=255 in the MS-DOS CONFIG.SYS file, you may not be able to access
 that many files at once in your program because there may not be
 enough memory available inside the DGROUP data segment to allocate
 file buffers. Also note that five file handles are taken up by the
 MS-DOS standard input/output devices.
 
 We recommend that you use the Basic SETMEM function to reduce the size
 of memory available to Basic as it loads. This method provides more
 memory to the operating system, which may be necessary to open
 more than 15 files at the same time. If the interrupt call fails
 with the return code of 8 (in OUTREGS.AX), indicating insufficient
 memory, use the SETMEM function to force Basic to release some memory
 to MS-DOS to make more memory available for file handles.
 
 You almost always need to use the SETMEM function if you are calling
 this interrupt in an MS-DOS session running in Microsoft Windows (the
 call to the interrupt returns with the carry flag set and AX = 8,
 indicating insufficient memory). In addition to using SETMEM to run
 this program under Microsoft Windows, you must also add/increase
 "perVMFILES=n", where n is 0 to 255 (default 10) in the [386enh]
 section of the Windows SYSTEM.INI file. This entry specifies the
 number of private file handles that Windows should allocate to each
 virtual machine. For this entry to take effect, you must NOT use the
 SHARE.EXE utility. If Share is installed, this setting is ignored.
 
 To call the "set handle count" interrupt, load 67h into the AX
 register, and load the number of desired handles in the BX register.
 Under MS-DOS version 3.3, you must use an odd number ranging from 21
 to 255 for the number of desired handles, because even numbers may
 make the interrupt fail. This problem was corrected in MS-DOS
 version 3.30a. Even or odd numbers can be used for the number of
 desired handles when using Interrupt 67h in MS-DOS version 3.30a.
 
 The following is a Basic code example that uses an MS-DOS interrupt
 to access more than 20 MS-DOS file handles.
 
 Code Example
 ------------
 
 ' To run this program in the environment, you must invoke the
 ' environment with the /L switch to load the default Quick library:
 '    VBDOS.EXE /L          for Visual Basic 1.0 for MS-DOS
 
 ' To try this example in VBDOS.EXE:
 ' 1. From the File menu, choose New Project.
 ' 2. Copy the code example to the Code window.
 ' 3. Press F5 to run the program.
 
 ' Use the following include file for Visual Basic 1.0 for MS-DOS:
 REM $INCLUDE: 'VBDOS.BI'
 DIM InRegs AS RegType, OutRegs AS RegType
 y = SETMEM(-16384)   ' Must usually SETMEM in MS-DOS session under
                      ' Windows.
 
 InRegs.ax = &H6700         ' SetFileHandles function.
 ' Value in BX register must be odd in MS-DOS version 3.3; odd or even
 '  in later MS-DOS versions; ranging from 21 to 255:
 x = 30
 InRegs.bx = x              ' x is the number of files to open.
 CALL INTERRUPT(&H21, InRegs, OutRegs)
 
 FOR I% = 1 TO x - 5 ' Five file handles are reserved for MS-DOS
                     ' standard I/O.
   File$ = "Junk" + STR$(I%)
   OPEN File$ FOR OUTPUT AS I%
   PRINT I%
 NEXT
 END