Isolation: Why Must Shared Systems Limit Mutual Interference?

Isolation limits how one part of a shared environment can affect another. It does not reject connection; it makes connection pass through defined boundaries. Two programs may run on the same computer and share its processor and storage, yet neither should be free to read the other's memory. A crash in one should not automatically bring down the other.

Isolation is related to encapsulation but is not identical to it. Encapsulation defines the interface through which outsiders reach an internal state; isolation asks whether effects can spread across a boundary. Nor is isolation the same as complete separation. Removing every shared resource may reduce interference, but it also removes collaboration and efficiency.

The value of isolation is that sharing creates both benefits and paths along which faults, mistakes and conflicts can travel. Good isolation does not lock every component in a sealed room. It identifies which resources may be shared, which states must remain independent, and how cross-boundary effects are stopped. What it protects is not separateness for its own sake, but the ability to keep operating together.