Operating systems — compatibility across versions: Higher versions of an operating system are often designed so that programs built for earlier versions still run without changes. What is this property commonly called in legacy terminology?

Introduction / Context:
When platforms evolve, preserving the ability to run older applications is critical for users and enterprises. Terminology varies across eras and vendors, but the concept is widely recognized in operating systems, databases, and compilers.

Given Data / Assumptions:

• Newer OS version should run applications built for previous versions unmodified.
• The question uses legacy phrasing common in older exam banks and vendor literature.
• We are selecting the best fit among the given choices.

Concept / Approach:

Modern terminology typically calls this backward compatibility (new system runs old software). In older or vendor specific usage, the same idea was often labeled upward compatibility from the perspective of the application moving upward to a new system version. Among the provided options, “Upward compatibility” best matches the described behavior.

Step-by-Step Solution:

Verification / Alternative check:

Vendor release notes often promise “upward compatible” interfaces, meaning applications written for prior releases continue functioning on the upgrade, aligning with the prompt.

Why Other Options Are Wrong:

• Upgradability: ability to upgrade a system, not compatibility of apps.
• Upward mobility: not a software term.
• Universality: too vague; does not denote version-to-version compatibility.
• None of the above: incorrect because a matching term is provided.

Common Pitfalls:

Mixing directions: “backward compatibility” vs. “forward compatibility.” Here, the new system supports old apps, which many older sources called “upward compatibility.”

Final Answer:

Upward compatibility