Draft Document for Review April 7, 2004 6:15 pm

6947ch04.fm

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Chapter 4. Channel Subsystem

This chapter describes how the Channel Subsystem (CSS) is implemented on the z990. Each server has a Channel Subsystem. Its role is to control communication of internal and external channels to control units and devices. The configuration definitions of the CSS define the operating environment for the correct execution of all system Input/Output (I/O) operations. The CSS provides the server communications to external devices via channel connections. The channels permit transfer of data between main storage and I/O devices or other servers under the control of a channel program. The CSS allows channel I/O operations to continue independently of other operations within the central processors.

The architecture and functionality of the CSS is significantly enhanced on the z990. The implementation of the Channel Subsystem is significantly different from those on previous zSeries servers.

This chapter introduces the concept of multiple Logical Channel Subsystems (LCSSs) implemented on the z990. The goal of this chapter is to make you familiar with the technology, terminology, and implementation aspects of the z990 Channel Subsystem design. The multiple Logical Channel Subsystem (LCSS) and related components are described in:

￿“Multiple Logical Channel Subsystem (LCSS)” on page 110

￿“Logical Channel Subsystem structure” on page 110

￿“LCSS configuration management” on page 115

￿“LCSS-related numbers” on page 117

© Copyright IBM Corp. 2004. All rights reserved.

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990 specifications

The IBM 990 series, often referred to in the context of IBM's pioneering efforts in the realm of mainframe computing, represents a unique chapter in the history of information technology. Introduced in the late 1960s, the IBM 990 series was designed as a powerful tool for enterprise-level data processing and scientific calculations, showcasing the company's commitment to advancing computing capabilities.

One of the main features of the IBM 990 was its architecture, which was built to support a wide range of applications, from business processing to complex scientific computations. The system employed a 32-bit word length, which was advanced for its time, allowing for more flexible and efficient data handling. CPUs in the IBM 990 series supported multiple instructions per cycle, which contributed significantly to the overall efficiency and processing power of the machines.

The technology behind the IBM 990 was also notable for its use of solid-state technology. This provided a shift away from vacuum tube systems that were prevalent in earlier computing systems, enhancing the reliability and longevity of the hardware. The IBM 990 series utilized core memory, which was faster and more reliable than the magnetic drum memory systems that had been standard up to that point.

Another defining characteristic of the IBM 990 was its extensibility. Organizations could configure the machine to suit their specific needs by adding memory, storage, and peripheral devices as required. This modular approach facilitated the growth of systems alongside the technological and operational demands of the business environments they served.

In terms of software, the IBM 990 series was compatible with a variety of operating systems and programming environments, including FORTRAN and COBOL, enabling users to access a broader array of applications. This versatility was a significant advantage, making the IBM 990 an appealing choice for educational institutions, research facilities, and enterprises alike.

Moreover, the IBM 990 was engineered to support multiprocessing, which allowed multiple processes to run simultaneously, further increasing its effectiveness in tackling complex computing tasks.

In summary, the IBM 990 series represents a significant advancement in computing technology during the late 20th century. With a robust architecture, versatile configuration options, and a focus on solid-state technology, the IBM 990 facilitated substantial improvements in data processing capabilities, making it a cornerstone for many businesses and academic institutions of its time. Its impact can still be seen today in the continued evolution of mainframe computing.
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