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 Extend 6.0 - Open More Files than DOS Standard 20   Scott Bussinger 06.12.1992

This unit allows a program to open more than the standard DOS maximum of 20 open files at one time.



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EXTEND.PAS Version 6 November 30, 1992 by Scott Bussinger Compuserve 72247,2671 MS-DOS and PC-DOS Turbo Pascal 3.0 and higher only allow up to 15 files to be open at the same time, due to limitations in DOS. This file shows you how to have up to 96 files open simultaneously under DOS 2.0 or 2.1, or 252 files open simultaneously under DOS 3.0 or higher. Below is a description of how to use this technique, followed by a technical explanation of the implementation, for those who are interested. Note this documentation is liberally based on the original EXTEND.PAS documentation by Randy Forgaard, but has been renamed to EXTEND.DOC and modified by Scott Bussinger to reflect the changes to involved in versions 2 and 3. TO USE THIS TECHNIQUE: You simply include the EXTEND unit in the USES statement in the source code of your main program. You will have to either compile the EXTEND unit separately or use Turbo Pascal 4.0's project compiling features to Make or Build your program (which will compile the EXTEND unit automatically). The EXTEND unit should be the first unit in your USES statement, following only the DOS unit (which is USEd by the EXTEND unit). The unit automatically installs itself and will uninstall itself when your program ends or an error is detected. See the demo program below for an example of using the EXTEND unit. The EXTEND.PAS file will need to be available available to be compiled if the Make or Build features are used to compile the program. The EXTEND.ASM is the source code for the assembly language interrupt handler used when running under DOS 2. The EXTEND.OBJ file is the assembled object code for EXTEND.ASM and was compiled using A86, a shareware compiler available on Compuserve and other bulletin boards. You must edit your CONFIG.SYS file (see the DOS manual for details), so that it includes a line that says "FILES=XXX". XXX should be a number that is at least 3 greater than the maximum number of files that will be in use (opened by RESET, REWRITE or APPEND) at the same time during the execution of your program (larger values will provide no additional benefit, with respect to your individual program), and should not exceed 99 (for DOS 2.0/2.1) or 255 (for DOS 3.0 and higher). Under any version of DOS, the minimum allowable value for XXX is 8. Then, reboot your computer so that the FILES=XXX parameter takes hold. This same change to the CONFIG.SYS file will have to be made on any machine in which your program is to run. Running the sample program will tell you the maximum number of files you can have open at once (usually 3 less than the number of files specified in the CONFIG.SYS file as discussed above, unless a resident program has opened some files and hasn't closed them yet). Scott Bussinger Professional Practice Systems 110 South 131st Street Tacoma, WA 98444 (206)531-8944 Compuserve [72247,2671]