Mainframe computers are powerful devices that are mainly used by big companies for critical applications and bulk data processing. The name comes from their substantial size and certain power requirements. It originally referred to the sizeable cabinets where the central processing unit and main memory were located; today, however, it is used to distinguish high-end commercial machines from less powerful ones. In the 1960s, most significant computer system designs were set and established based on architecture created during that era. During this time, the defining characteristics of mainframe computers were firmly set, and as time has gone on, they have evolved and become more complex.
Modern mainframe computers have abilities based on their surplus of internal engineering and high reliability and security, as well as their extensive input-output facilities, strict backward compatibility with older software, and high utilization rates to support massive throughput. They also maintain a quick single task computational speed. These devices often run for years without interruption because their repairs and hardware upgrades can be done while they are operating normally.
Early mainframes had no interactive interface. They accepted sets of punched cards, paper tape, and magnetic tape and functioned exclusively in batch mode to support back office tasks like invoicing. By the 1970s, many mainframes had finally acquired interactive user interfaces and ran as timesharing computers while supporting hundreds of users at the same time. Users acquired access by way of specialized terminals or from personal computers that had terminal emulation software. Many mainframes supported graphical terminals, but did not support graphical user interfaces. Presently, most mainframes have phased out classic terminal access for end-users supporting Web user interfaces.
Almost all mainframes are able to host several operating systems, thus operating as a number of virtual machines. When doing so, one mainframe can replace up to hundreds of smaller servers. Virtualization is now available on most lines of computer systems with varying levels of complexity.
Mainframe models are designed to handle very great amounts of volume input and output and emphasize throughput computing. They have almost always included several subsidiary computers, such as channels and peripheral processors, which manage the I/O devices. This in turn leaves the CPU open to deal with high-speed memory and considerable databases and files. Mainframe return on investment is dependent on its ability to scale, support mixed workloads, lessen labor costs, provide uninterrupted service for critical business applications, and many other factors. Mainframes also have execution integrity characteristics for fault tolerant computing.