6947ch02.fm

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

Activation of logical partitions as well as dynamic storage reconfiguration will cause the storage to be assigned to the type needed (CS or ES). This does not require a Power-on Reset. No new software support is required to take advantage of this function.

Hardware System Area (HSA)

The Hardware System Area (HSA) is a non-addressable storage area that contains the CPC Licensed Internal Code and configuration-dependent control blocks. The HSA size varies according to:

￿The number of defined logical partitions.

￿If dynamic I/O is not enabled, the size and complexity of the system I/O configuration. The HSA may hold the configuration information for up to 63 K devices per LCSS.

￿If dynamic I/O is enabled, the MAXDEV value specified in HCD or IOCP, in support of dynamic I/O configuration.

Note: The HSA is always allocated in the physical memory of Book 0.

2.2.6 Modes of operation

Figure 2-15 on page 57 shows the z990 modes of operation diagram, summarizing all available mode combinations that are discussed in this section: z990 mode, image modes and their processor types, operating system versions and releases, and architecture modes.

Note: The z990 models only operate in Logically Partitioned Mode. ESA/390 TPF mode is now only available as an image mode in a logical partition.

There is no special operating mode for the 64-bit z/Architecture mode, as the architecture mode is not an attribute of the definable images operating mode.

The 64-bit operating systems are IPLed into 31-bit mode and, optionally, can change to 64-bit mode during their initialization. It is up to the operating system to take advantage of the addressing capabilities provided by the architectural mode.

The operating systems supported on z990 servers are shown in “Software support” on page 133.

56IBM eServer zSeries 990 Technical Guide

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IBM 990 manual Modes of operation, Hardware System Area HSA
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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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