How does a counting semaphore differ from a binary semaphore?

• A. A counting semaphore can have a range of counts higher than 1, while a binary semaphore is limited to 0 or 1.
• B. A counting semaphore cannot be used for signaling.
• C. A binary semaphore can have values 0, 1, or 2.
• D. There is no functional difference.

Answer: (A)

The key distinction is that a counting semaphore can represent multiple units of a resource, while a binary semaphore is limited to a single unit. A counting semaphore maintains a count that can be greater than 1, reflecting how many identical resources are available. Its wait (decrement) and signal (increment) operations adjust that count, and threads can proceed as long as the count remains above zero, allowing several threads to hold the resource concurrently up to the available amount. A binary semaphore, on the other hand, can only be 0 or 1, which makes it ideal for mutual exclusion or a simple on/off flag since it prevents more than one holder at a time. This fundamental difference in the range of values is why a counting semaphore is appropriate for scenarios with multiple identical resources, whereas a binary semaphore is used when only one resource unit should be controlled at a time.