Which statement correctly differentiates vertical scaling, horizontal scaling, and sharding?

• A. Vertical scaling adds resources to a single server; horizontal scaling adds more servers; sharding partitions data across multiple databases to scale horizontally.
• B. Vertical scaling adds more servers; horizontal scaling adds resources to a single server; sharding duplicates data across servers.
• C. Vertical scaling partitions data across databases; horizontal scaling adds resource to a single server; sharding increases CPU frequency.
• D. Vertical scaling is about caching; horizontal scaling is about load balancing; sharding is unrelated.

Answer: (A)

Vertical scaling, horizontal scaling, and sharding describe how to grow a system to handle more load. Vertical scaling means upgrading a single machine—the CPU, memory, and storage you put into one server. Horizontal scaling means adding more machines to share the workload, spreading requests across multiple servers. Sharding is a technique used in conjunction with horizontal scaling: it partitions the data itself across multiple databases or servers, so each shard stores only a portion of the total data and handles part of the workload.

This option is correct because it matches those definitions precisely: one server is enhanced (vertical), more servers are added (horizontal), and data is partitioned across multiple databases to scale horizontally (sharding).

The other descriptions mix up the ideas. Vertical scaling isn’t about adding multiple servers, horizontal scaling isn’t about boosting resources on a single server, and sharding isn’t simply duplicating data or increasing CPU frequency. It’s about partitioning data across multiple storage nodes to distribute load.