6947ch07.fm

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

7.2.7 Dynamic CF dispatching and dynamic ICF expansion

The CF Control Code (CFCC), the “CF Operating System,” is implemented using theActive Wait technique. This means it is always running (processing or searching for service) and never enters into a wait state. This also means that it gets all the processor capacity (cycles) available for the Coupling Facility logical partition. If this logical partition uses only dedicated processors (CPs or ICFs), this is not a problem. But this may not be desirable when it uses shared processors (CPs or ICFs).

Dynamic CF dispatching provides the following function on a Coupling Facility: If there is no work to do, it enters into a wait state (by time). After an elapsed time, it wakes up to see if there is any new work to do (requests in the CF Receiver buffer). If there is no work, it will sleep again for a longer period of time. If there is new work, it enters into the normal Active Wait until there is no more work, starting the process all over again. This saves processor cycles and is an excellent option to be used by a production backup CF or a testing environment CF. This function is activated by the CFCC command DYNDISP ON.

The z990 CPs can run z/OS and/or OS/390 operating system images and CF Images. For software charge reasons, it is better to use ICF processors to run Coupling Facility images.

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Figure 7-5 z990 Dynamic CF Dispatching (shared CPs or shared ICF PUs)

With Dynamic ICF Expansion, a Coupling Facility image using one or more dedicated ICFs can also use one or more shared CPs of this same server. The Coupling Facility image uses

the shared CPs only when needed, that is, when its workload requires more capacity than its dedicated ICFs have. This may be necessary during peak periods or during recovery processes.

Figure 7-6 on page 167 shows an example where the server on the left has a production and a test Coupling Facility that has dedicated and shared ICF PUs. This configuration enables the Coupling Facilities to utilize the shared ICF PUs when workload becomes excessive. Additionally, if the alternate production Coupling Facility goes down (for maintenance, for example) and the allocated ICFs’ capacity on the left server is not big enough to maintain its own workload plus that of the other Coupling Facility, then with Dynamic ICF Expansion, the remaining Coupling Facility image can be expanded over shared ICF PUs.

166IBM eServer zSeries 990 Technical Guide

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IBM manual Dynamic CF dispatching and dynamic ICF expansion, Z990 Dynamic CF Dispatching shared CPs or shared ICF PUs

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.