Characteristics of a Mainframe Computer
Although many believe that mainframe computers are dinosaurs headed toward extinction, the large companies of the world still run on mainframe computers. These companies require the stability, scalability and security offered by mainframe computing. This type of computer monolith can carry environmental and other support requirements but provide staggering computing power to companies that employ it.
One of the most obvious differences in mainframe computers versus their smaller counterpart servers lies in their sheer size. In the early days of computing, mainframes filled large rooms and ran on vacuum tubes that consumed large amounts of electricity. Modern mainframes provide considerably more computing power in far less space while consuming far less power. While some "mainframes" may indeed only take up a desktop, the true mainframe workhorses that power large computing environments are indeed still sizable.
Speed and Throughput
Mainframe computers are designed to maximize throughput, handling large amounts of data and transactions in extremely short periods. Large businesses such as banks, credit card processors and other financial institutions rely on this ability to handle large volumes of input and output to make real-time information available to their customers. At one point, this speed was measured in millions of instructions per second (MIPS). Due to the other factors that contribute to throughput speed, technicians developed a more humorous definition: "meaningless indicator of processor speed." With this realization came the development of new measurements that indicated actual workload throughput more accurately.
As mainframe sizes have shrunk, so have the once-voluminous power requirements. However, the need for reliability dictates that the power supplied to mainframe computers be clean power. Spikes and surges in power can damage computing components and lead to minor data dropouts that can cause untold headaches. For this reason, mainframes require uninterruptible power supplies (UPSs) that provide constant clean power.
Two of the biggest enemies of mainframe computers are heat and dust, so establishing a mainframe data center comes with significant environmental concerns. The mainframe room must be clean, cool and well ventilated. These machines generate a great deal of heat; cool air must remain in constant circulation to prevent damage to critical computing components.
Perhaps the biggest difference in mainframe computers versus departmental and other servers has to do with the operating systems they run. Mainframes typically run larger and more robust systems such as Z/OS, MVS, VSE and OS/390. These are far more powerful and reliable than the desktop and server operating systems that have proliferated in smaller companies.