processes' filter functions and buffers -- data chunks

[Peter Tury]

Hi,

I read in (elisp)Filter Functions that "[A process'] output to the
[filter] function may come in chunks of any size.  A program that
produces the same output twice in a row may send it as one batch of
200 characters one time, and five batches of 40 characters the next."

What determines how and why this splitting happens? Is this an Emacs
feature? Or depends only on the process (e.g. the program what Emacs
connects to)? Or is this OS-dependent?

I see some similar thing happening in the process' buffer also:
sometimes I can't see the process' output until more output
arrives. It seems the output is buffered somewhere and it doesn't
displayed in the associated Emacs buffer until that (OS?) buffer is
filled up. (I use official GNU Emacs v22 on MS Windows XP.) However,
output is OK (=always showed up completely) in "Command/DOS windows",
thus it seems this is Emacs "feature"??

I found this "unpredictable" splitting quite annoying and I don't know
if I have chance to avoid this behaviour by modifying the peer program
or I absolutely have to live with this feature?

Thanks,
P