6947ch04.fm

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

4.1 Multiple Logical Channel Subsystem (LCSS)

The concept of Logical Channel Subsystem (LCSS) is new to the z990. The z990 supports up to four Logical Channel Subsystems, hence the term multiple Logical Channel Subsystem. The design of the z990 offers a considerable increase in processing power, memory sizes, and I/O connectivity. In support of the larger I/O capability, the Channel Subsystem has been scaled up correspondingly and the LCSS concept is designed to do just that. This concept is introduced to facilitate the architectural change that provides more logical partitions and more channels than before.

The structure provides up to four Logical Channel Subsystems. Each LCSS may have from 1 to 256 CHPIDs, and may in turn be configured with up to 15 logical partitions that relate to that particular Logical Channel Subsystem. LCSSs are numbered from 0 to 3, and are sometimes referred to as the CSS Image ID (CSSID 0, 1, 2, and 3).

Note: The z990 provides for four Logical Channel Subsystems, 1024 CHPIDs, and up to 30 logical partitions for the total system.

Table 4-1 shows the number of logical partitions and CHPIDs supported.

Table 4-1 Logical partitions and CHPID numbers support

LCSS

Number of

Number of

Number of server

supported

active LPARs

defined LPARs

CHPIDs supported

 

 

 

 

LCSS 0, 1, 2, 3

30

30

1024

 

 

 

 

4.1.1 Logical Channel Subsystem structure

The provision for multiple LCSSs is an extension to that provided on previous z/Architecture servers. It provides channel connectivity to the defined logical partitions in a manner that is transparent to subsystems and application programs.

The LCSS introduces new components and terminology that differs from previous server generations. These components are explained in the following sections.

Logical Channel Subsystem (LCSS)

The z990 provides the ability to define more than 256 CHPIDs because of the introduction of Logical Channel Subsystem concept. An LCSS is a logical replication of CSS facilities (subchannels, CHPIDS, controls, and so on). This enables the definition of a balanced configuration for the processor, and I/O capabilities. The LCSSs of the z990 introduce significant changes to the I/O configuration.

For ease of management, it is strongly recommended that HCD be used to build and control your z990 Input/Output Definition file (IODF). HCD support for z990 multiple logical channel subsystems is available beginning with z/VM 4.4 and is available on all current OS/390 and z/OS levels. HCD provides the capability to make both dynamic hardware and software I/O configuration changes.

A z990 must have at least one LCSS defined. No logical partitions can exist without at least one defined LCSS. Logical partitions are defined to an LCSS, not to a processor. Up to four LCSSs are supported on the z990, and a logical partition is associated with one and only one LCSS. CHPIDs are unique within an LCSS and range from 00 to FF. The same CHPID number range is used again for the other LCSSs.

110IBM eServer zSeries 990 Technical Guide

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IBM 990 manual Multiple Logical Channel Subsystem Lcss, Logical Channel Subsystem structure
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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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