6947ch02.fm

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

For detailed information about the I/O system structure, see“I/O system structure” on page 73.

2.2.13 Channel Subsystem

The representation of all connections and devices is called the Channel Subsystem. The z990 introduces the concept of Multiple Logical Channel Subsystems. Up to two Logical Channel Subsystems (LCSSs) can be defined in the IOCDS, and this allows for the definition of up to 512 channels. One IOCDS describes the complete I/O configuration and one HSA after Power-On Reset (POR). The HSA is always located in the physical memory of Book 0.

Logical Channel Subsystem (LCSS)

A Logical Channel Subsystem (LCSS) is a logical collection of up to 256 CHPIDs that are mapped to physical channels with the assistance of HCD, the Channel Mapping Tool (CMT), and IOCP. Physical channels are represented in the system by Physical Channel IDs (PCHIDs). The z990 supports up to two LCSSs (512 CHPIDs), but the Multiple CSS architecture allows for more LCSSs.

Physical Channel ID (PCHID)

PCHIDs identify the physical ports on cards located in I/O cages and follow the numbering scheme listed in Table 2-11.

Table 2-11 PCHID locations

Cage

Front PCHID ##

Rear PCHID ##

 

 

 

I/O Cage 1

100 - 1FF

200 - 2FF

 

 

 

I/O Cage 2

300 - 3FF

400 - 4FF

 

 

 

I/O Cage 3

500 - 5FF

600 - 6FF

 

 

 

CEC Cage

000 - 0FF reserved for ICB-4

 

 

 

Introduction of PCHIDs means that CHPIDs are no longer pre-assigned. It is the responsibility of the user to assign the CHPID numbers through the use of HCD/IOCP, and the CHPID mapping tool. Assigning a CHPID means that the CHPID number is associated with a physical channel port location (PCHID) and an LCSS (LCSS0 or LCSS1). CHPID numbers still range from 00 to FF and must be unique within an LCSS.

For more detailed information about the Logical Channel Subsystem structure, see “Logical Channel Subsystem structure” on page 110.

72IBM eServer zSeries 990 Technical Guide

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IBM 990 manual Logical Channel Subsystem Lcss, Physical Channel ID Pchid, Cage Front Pchid ## Rear Pchid ##
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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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