This article is from a FAQ concerning SCO operating systems. While some of the information may be applicable to any OS, or any Unix or Linux OS, it may be specific to SCO Xenix, Open There is lots of Linux, Mac OS X and general Unix info elsewhere on this site: Search this site is the best way to find anything.
Each process generally consists of several (usually, but not always, three) regions - typically code, data, and stack. Two copies of the same program running at the same time will often share code, reducing the number of regions required; however, there's nothing to stop a program from using more than three regions, either.
There is a tunable kernel parameter, NREGION, which specifies the maximum number of regions available. This should always be set to at least three times the number of processes (NPROC), and if you want to be on the safe side, use four times NPROC. Note that in OSR5, by default, both NREGION and NPROC are allocated dynamically.
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