In distributed systems, what does horizontal scaling mean?

• A. Adds more machines to the pool
• B. Increases the power of existing machines
• C. Upgrades single machine's memory
• D. Uses more efficient algorithms

Answer: (A)

Horizontal scaling means adding more machines to the pool to handle growing load by distributing work across multiple nodes. This approach lets you increase capacity linearly as demand rises and improves fault tolerance, since other machines can keep serving requests if one node fails. In contrast, increasing the power of existing machines or upgrading a single machine’s memory (vertical scaling) raises capacity of a single node but has practical limits and can create a bottleneck if that node goes down. Using more efficient algorithms can speed things up, but it doesn’t by itself expand the system with additional machines.