use of _s[io]buf in stdio library

[G|sta Simil{/ml]

Has anyone got a idea why the stdio-package declares but never
uses two buffers, "_sibuf" and "_sobuf"?
They are declared as s[io]buf[BUFSIZ] in s[io]buf.c (4.2 bsd).
I have thought about using them in my own programs, maybe that's
even what they are for!?
Just grepped through some of the source. Some programs use setbuf()
to make use of _sobuf. Strange was however that most of this programs
seems to be programs who looks into kernel memory, ps, sps, w, who etc.

		G|sta Simil{	gostas at kuling.UUCP