Vertical scalability, also known as "scaling up," refers to the ability to increase the capacity of a single server or machine. This can be achieved by adding more resources, such as CPU, RAM, or storage, to enhance performance. Vertical scalability is often simpler to implement since it involves upgrading existing hardware rather than distributing workloads across multiple systems. However, vertical scalability has its limitations. There is a maximum capacity that a single machine can reach, and once that limit is hit, further upgrades may not be possible. This contrasts with horizontal scalability, where additional machines are added to handle increased load, allowing for more flexibility and potential growth.