Processors - IBM Mainframe

The central components of mainframe computer systems are the processors. MVS runs on processors that are members of the System/360-370 family, a group of processors that has evolved over a period spanning nearly 30 years. The System/360-370 family includes the System/360 models of the mid-1960s, the System/370 models of the early 1970s, the 3030 models of the late 1970s, the 4300 and 3080 models of the early 1980s, and the 3090 systems of the late 1980s. Recent members of this family are the ES/9000, S/390 and z-series systems, but many installations still run older 4300, 3080, and 3090 systems.

The Basic Architecture of the 370-Series Processor

The Basic Architecture of the 370-Series Processor

As IBM has developed new models of System/360-370 processors, it has used contemporary technologies to create better, faster, and cheaper machines. Although the older System/360 and System/370 models are obsolete, the current 4300, 3080, 3090, and ES/9000 processors are still generally called System/370s. That is because even though the technology has changed significantly, IBM has enhanced the basic operating characteristics of the processors in ways that have allowed the System/370 family to maintain a high degree of compatibility over its nearly 30 year life. And we can expect that future members of the System/370 family will maintain that compatibility as well.

The above figure shows the basic arrangement of the subcomponents that make up a typical System/370-type processor. As you can see, the processor consists of three main parts: CPU, main storage, and channels. From a general point of view, this basic configuration applies to all System/370-type computers, including the 4300, 303X, 308X, 3090, ES/9000 and S/390 computers. The arrangements of these basic components are more complex in processors with greater processing power.

The central processing unit, or CPU, contains the circuitry needed to execute program instructions that manipulate data stored in main storage, also called main memory. Although the above figure does not show it, most System/370 processors use a special purpose high-speed memory buffer called a cache that operates between the CPU and main memory. This relatively small amount of storage operates at speeds even faster than the storage in main memory, so the overall speed of the processor is increased.

Special circuitry constantly monitors accesses to main memory and keeps the most frequently accessed sections in the cache. Certain System/370 processors also include an additional type of memory called expanded storage. Expanded storage is not directly available to application programs. Instead, it is used much as if it were a high-speed disk device. You will learn more about the role of expanded storage in the next chapter.

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