Memory management on 286 and later PCs under DOS 5 1. It is now possible to load any device drivers that follow into UMBs. Some increase in size after they're loaded and, if they can't, may cause the PC to lock-up. But, again, it isn't sensible to load them all high. Again, they should be loaded high, largest first.
All batch files have a .BAT extension and are executed by typing their name.
For example you might have a batch file to run Microsoft Word 5, called W5.BAT, which you would execute by typing W5. And basically it can't be done - not in one go anyway. Intermittently someone deletes the system files stored in the root directory of drive C and the next time they boot their PC get 'Bad or Missing Command Interpreter'. It's not even safe to run up Word and check what you've lost, because Word creates temporary files which may overwrite what you've deleted. Howewver each child process will always have a COPY of all the environment variables of its parent.