What is the difference between soft and hard faults in reliability testing?

• A. Soft faults are intermittent/transient; Hard faults are permanent.
• B. Soft faults are permanent; Hard faults are intermittent.
• C. Soft faults relate to software; Hard faults relate to hardware.
• D. Soft faults are visible; Hard faults are invisible.

Answer: (A)

Soft faults are intermittent or transient faults that can appear and then disappear, often due to temporary conditions, marginal connections, or noise. Hard faults are permanent failures where the device no longer meets specifications and remains faulty until repair or replacement. This distinction matters because it drives how you test: soft faults require observing the system over time and through different conditions to catch those reversible glitches, while hard faults show up consistently and indicate a lasting defect. The other choices mix up permanence, or confuse the idea with software vs hardware or visibility, which doesn’t capture the reversible versus irreversible nature of these faults.