A personal computer (PC) differs from a mainframe computer primarily in terms of size, cost, and processing power. PCs are designed for individual use and are typically affordable, allowing users to perform tasks such as word processing, gaming, and web browsing. In contrast, mainframe computers are significantly larger, more powerful, and used by large organizations for critical operations that require extensive data processing capabilities, like transaction processing and large-scale simulations. Mainframes also support numerous users simultaneously through multi-user capabilities.