Mainframe systems have been around for decades and remain operational today. When properly deployed, mainframes provide peak reliability, availability, serviceability, and security. They provide high throughput and process billions of transactions per day. Mainframes are still used today to run mission-critical applications in banking and financial institutions, airline, and retail industries.
Initial investment in mainframes was high because proprietary hardware and software made it expensive. IT operations required specially trained staff. Expertise to run present day mainframes is in increasingly short supply. Mainframes also consumed significant real estate and required a substantial investment in power and cooling to operate. These characteristics made mainframe technology only accessible to the largest organizations. To solve these challenges, the IT industry began moving to client/server architectures for hosting applications and data to lower costs and reduce complexity.