• $SystemID is a short string that identifies the type of computer system on which Mathematica is being run.
• Computer systems with the same $SystemID should be binary compatible, so that the same external programs and .mx files can be used.
• Sometimes binary compatibility may only be complete when the same version of the operating system is used.
is used in naming directories generated by DumpSave
• Values for $SystemID contain only alphanumeric characters and dashes.
• Typical values are "Windows", "PowerMac", "Linux" and "Solaris".
• New in Version 3.