fast file copying (was questions about a backup program ...)

[Robert A. Lerche]

In Microsoft C (and some others), one can use "setvbuf" to attach a large
I/O buffer to a stdio-package file.

It's sensible to wish for the operating system to do this itself, but in
the DOS world, given the 640K memory limit, it's not totally unreasonable to
place the memory allocation burden on the application program (since it
probably has to worry about tight memory).

Using "setvbuf" makes a biiiiiig difference in file I/O performance.