operating systems with their roots in DOS
which excludes NT and W2K, have a couple of device names that can be used as files.
CON and PRN are some of the more well-known ones.
You can actually enter
COPY AUTOEXEC.BAT CON
to output a file on the console window.
Nothing too spectacular - but there is another, rather unknown device: CLOCK$.
COPY CLOCK$ BLA.TXT
(wait for a couple of seconds)
and check the size of the remaining file with
CLOCK$ can be read (nice to produce not-that-random binary data, but it can also be used to write stuff to.
A favorite way to crash your own computer in the old days was using EDLIN CLOCK$ and rewriting it, which on many machines would ruin the BIOS settings, so Don't try this at home.