conditions of failure... malloc that is...

y'know how i asked about memory allocation and how to do error checking and all sorts of, more style-related ?uestions? well, aside from there being insufficient memory... [which is never the case, thanks to my two blazing 256 sticks... defrag was niice... 30 gigs in two hours...] is there any other condition in which malloc [calloc] could fail? and, how can i check all availiable ram left to use? i'm under djgpp/dos, y'know... thanks! i'll look up more on the latter, as i'm sure there's a command for it...