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.
- $SystemID is used in naming directories generated by DumpSave and .
- Values for $SystemID contain only alphanumeric characters and dashes.
- Typical values are , , and .
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