System 4 or System IV may refer to:

• Acorn System 4, the early minicomputer
• The fourth release of Classic Mac OS
• International Computers Limited#English Electric LEO Marconi (EELM), also known as ICL System 4
• Not-released Unix system between UNIX System III and UNIX System V
• STS-4 (Space Transportation System-4), the Space Shuttle mission

• IBM System/4 Pi

This disambiguation page lists articles associated with the title System 4.
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