You can partition your space to protect one program from another. For example, you can set aside one disk for receiving mail, and another disk for word processing. Under most operating systems, when you install a new disk, you can chop it into several limited partitions. Partitioning is not free. You will be unable to receive mail when your mail disk is full, for example, even if you have tons of space available on your word-processing disk.
Similar comments apply to other shared resources, such as CPU time.
Here are some of the limited resources on a UNIX machine, and some of the tools that you can use to manage those resources. You can limit the disk space used by a single uid with quotas . You can limit the size of files created by a single process with the filesize rlimit. The text segment contains program code. The stack segment contains stack frames.