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

Linux on zSeries (and Linux for S/390)

Linux on zSeries offers a number of advantages compared to other platforms. First, it puts the Linux applications close to the enterprise data and applications, thus reducing the chance for bottlenecks. And since a Linux application runs in its own partition, with its own dedicated resources, it does not impact the availability or security of the rest of the system.

A second advantage is the extremely reliable zSeries hardware, which can support up to 15 logical partitions on z900/z800 and up to 30 Linux logical partitions on z990—and thousands of Linux images if Linux is run as a guest operating system under z/VM. Consolidation of multiple Linux images on a single server can greatly simplify systems management.

With the large number of applications available in the open source community, many customers will find Linux gives them a relatively low-cost way to deliver and integrate new applications quickly. For others, Internet enablement may be quicker and easier when they extend existing applications. Either way, zSeries support for the Application Framework for e-business and Linux gives that choice and flexibility.

The choice of application source depends on a number of factors, including the source, the required qualities of service, and the time allowed for development.

1.3.16 Software support

Compatibility and exploitation

Generally speaking, software support for the z990 comes in two steps: Compatibility support and Exploitation support. However, there are variations specific to each operating system.

Compatibility support provides no additional functionality over and above a z900 or z800. Compatibility only provides PTFs that allow the operating system to run on z990 or coexist in a sysplex with z990.

Exploitation support provides the operating systems with the ability to take advantage of greater than 15 logical partitions and multiple Logical Channel Subsystems (LCSS).

OS/390 & z/OS

OS/390 R10 and z/OS 1.2 to z/OS 1.5 and later all provide Compatibility support. In addition, z/OS 1.4, and z/OS 1.5 or later will have Exploitation support for up to 30 logical partitions and four LCSSs. OS/390 supports both 31-bit and 64-bit modes, while z/OS 1.2 to z/OS 1.4 have the bimodal migration accommodation available for fallback to 31-bit mode for a period of up to 6 months.

Exploitation support can be installed on any z/OS 1.4 system, regardless of the hardware it is running on, but obviously uses functionality as provided by that hardware. The Exploitation support is include on z/OS 1.5 and later releases.

When z/OS or OS/390 has only Compatibility support applied, it is limited to running in LCSS0 and may not have an LPAR id greater than 'F'. In a z/OS only environment, if z/OS does not have exploitation support, then it is limited to only 15 active logical partitions and up to 256 CHPIDs. More partitions may be defined and may be physically installed, but they cannot be used.

With Exploitation support on z/OS 1.4 or later, it is possible to fully exploit the z990 capabilities. It is possible to define up to 4 LCSS with up to 256 CHPIDs in each. Up to 30 logical partitions may be defined across the 4 LCSS. z/OS 1.5 has Exploitation support delivered as part of the base function, but does not support 31-bit mode on z990.

20IBM eServer zSeries 990 Technical Guide

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IBM 990 manual Software support, Compatibility and exploitation, Linux on zSeries and Linux for S/390, OS/390 & z/OS
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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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