In general, the operating system imposes some “user limits”. Try:
[bash]$ ulimit -S -a
[bash]$ ulimit -H -a
[tcsh]$ limit
[tcsh]$ limit -h
If any application, while running, exceeds any of these limits, it will be killed (note also, on a i686 32-bit system, the address space is 4 GB; no such problem on a x86_64 64-bit system, as long as you have enough RAM plus “swap space” available).