Term of the Moment
disk mirroring
Definition: mainframe
A state-of-the-art computer for mission critical tasks. Today, mainframe refers to a class of ultra-reliable servers from IBM that is designed for enterprise-class and carrier-class operations.
IBM Is the Mainframe Vendor
For decades, IBM was the dominant vendor in the mainframe business. Although many tried to compete by offering compatible machines, they no longer do (see IBM-compatible mainframe). HP, Unisys, Sun and others make machines that compete with IBM mainframes in many industries but are mostly referred to as servers. In addition, non-IBM mainframe datacenters have hundreds and thousands of servers, whereas IBM mainframe datacenters have only a few machines.
There Is a Difference
One might wonder why mainframes cost hundreds of thousands of dollars when the raw gigahertz (GHz) rating of their CPUs may be only twice that of a PC costing 1,000 times less. Here's why...
Lots of Processors, Memory and Channels
Mainframes support symmetric multiprocessing (SMP) with several dozen central processors (CPU chips) in one system. They are highly scalable. CPUs can be added to a system, and systems can be added in clusters. Built with multiple ports into high-speed caches and main memory, a mainframe can address thousands of gigabytes of RAM. They connect to high-speed storage subsystems that can hold petabytes of data.
Enormous Throughput
A mainframe provides exceptional throughput by offloading its input/output processing to a peripheral channel, which is a computer itself. Mainframes can support hundreds of channels, and additional processors may act as I/O traffic cops that handle exceptions (channel busy, channel failure, etc.).
Super Reliable
Mainframe operating systems are generally rock solid because a lot of circuitry is designed to detect and correct errors. Every subsystem may be continuously monitored for potential failure, in some cases even triggering a list of parts to be replaced at the next scheduled maintenance. As a result, mainframes are incredibly reliable with mean time between failure (MTBF) up to 20 years!
Here to Stay
Once upon a time, mainframes meant "complicated" and required the most programming and operations expertise. Today, networks of desktop clients and servers are just as complex. Large enterprises have their hands full supporting thousands of machines running Windows, macOS, Unix and Linux.
Mainframe System
UNIVAC Mainframe
IBM Is the Mainframe Vendor
For decades, IBM was the dominant vendor in the mainframe business. Although many tried to compete by offering compatible machines, they no longer do (see IBM-compatible mainframe). HP, Unisys, Sun and others make machines that compete with IBM mainframes in many industries but are mostly referred to as servers. In addition, non-IBM mainframe datacenters have hundreds and thousands of servers, whereas IBM mainframe datacenters have only a few machines.
One might wonder why mainframes cost hundreds of thousands of dollars when the raw gigahertz (GHz) rating of their CPUs may be only twice that of a PC costing 1,000 times less. Here's why...
Lots of Processors, Memory and Channels
Mainframes support symmetric multiprocessing (SMP) with several dozen central processors (CPU chips) in one system. They are highly scalable. CPUs can be added to a system, and systems can be added in clusters. Built with multiple ports into high-speed caches and main memory, a mainframe can address thousands of gigabytes of RAM. They connect to high-speed storage subsystems that can hold petabytes of data.
Enormous Throughput
A mainframe provides exceptional throughput by offloading its input/output processing to a peripheral channel, which is a computer itself. Mainframes can support hundreds of channels, and additional processors may act as I/O traffic cops that handle exceptions (channel busy, channel failure, etc.).
Super Reliable
Mainframe operating systems are generally rock solid because a lot of circuitry is designed to detect and correct errors. Every subsystem may be continuously monitored for potential failure, in some cases even triggering a list of parts to be replaced at the next scheduled maintenance. As a result, mainframes are incredibly reliable with mean time between failure (MTBF) up to 20 years!
Once upon a time, mainframes meant "complicated" and required the most programming and operations expertise. Today, networks of desktop clients and servers are just as complex. Large enterprises have their hands full supporting thousands of machines running Windows, macOS, Unix and Linux.
Mainframes have provided computing power for major corporations for more than 60 years. Sperry Rand (Univac), IBM, GE, RCA, NCR, Burroughs, Honeywell and Control Data were the first mainframe companies in the U.S. This picture was taken in the mid-1970s. See BUNCH. (Image courtesy of Unisys Corporation.)