Use the handle file functions exclusively and extend full path support throughout your application (being sure to allow for the maximum possible path length during user input of filenames). Use buffered I/O whenever possible. The device drivers in MS-DOS versions 2.0 and later can handle strings as long as 64 KB, and performance will be improved if you write fewer, larger records as opposed to many short ones.
Avoid the use of FCBs, the Int 25H or Int 26H functions, or the ROM BIOS disk driver. If you must use FCBs, close them when you are done with them and don't move them around while they are open. Avoid reopening FCBs that are already open or reclosing FCBs that have already been closed——these seemingly harmless practices can cause problems when network software is running.