macOS and air conditioner: what they have in common

1. Step 1. macOS — evolved from — Unix. Modern macOS is built on Unix.
2. Step 2. Unix — evolved from — Time-sharing. It grew out of Multics.
3. Step 3. Time-sharing — uses — Mainframe. Multi-user mainframes.
4. Step 4. Mainframe — has part — Integrated circuit. The hybrid circuits of the System/360.
5. Step 5. Integrated circuit — uses — Cleanroom. Production in cleanrooms.
6. Step 6. Cleanroom — uses — Air conditioner. Air filtration.

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