￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ 2GB

￿

￿

￿

￿

￿

￿

￿

￿

￿

￿

￿ J ￿ C ￿ D ￿ R ￿ T ￿ V ￿ U ￿ B ￿ B ￿

￿

￿

￿

￿

￿

￿

￿ N ￿

￿

￿

￿ E ￿ I ￿ F ￿ A ￿ S ￿ T ￿ I ￿ A ￿ A ￿

￿

￿

￿

￿

￿

￿

￿ X ￿

￿

￿

￿ S ￿ C ￿ S ￿ C ￿ O ￿ A ￿

￿ T ￿ T ￿

￿

￿

￿

￿

￿

￿

￿ S ￿

￿

￿

￿

￿ S ￿ M ￿ F ￿

￿ M ￿ R ￿ C ￿ C ￿

￿

￿

￿

￿

￿

￿

￿ V ￿

￿

￿

￿

￿

￿ S ￿

￿

￿

￿ C ￿ H ￿ H ￿

￿

￿

￿

￿

￿

￿

￿ S ￿

￿

￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿

￿

 

￿

￿

MVS NUCLEUS

￿

￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿￿ 0

Figure 4. OS/390 Storage Layout

Figure 4 depicts a typical OS/390 system including the various functional subsystems, each running in its own address space. As in VSE/ESA, each address space has the ability to address up to 2GB of virtual storage.

1.2.3.2 N-way Processor Support

VSE/SP did not provide support for multiple processors (that is, n-way machines). Users, for a variety of reasons, exceeding the capacity of a single engine (Uni-processor) found it necessary to convert to OS/390 for its multiprocessor support. As was mentioned with virtual storage, typically these were users with a requirement for multiple CICS and batch partitions. The Turbo Dispatcher support in VSE/ESA V2 provided support for n-way processors. However, in the current version of VSE/ESA V2.2 a practical limit of only being able to support a 3-way processor exists. The number of parallel and

non-parallel tasks that exist within the system workload will determine the actual number of processors that can be effectively utilized.

1.2.3.3 Task Quantity

As was mentioned in the case of business consolidations, task quantity relates to the amount of concurrent work in the system. In the consolidations example several system images (workloads) are combined into a single system image. As was also mentioned, the previous VSE system limit of 12 partitions severely limited the ability to run very large workloads; particularly those consolidated workloads requiring more that 12 partitions. The solution was to run multiple VSE images. This often created issues of managing multiple images, or deciding to migrate to OS/390.

1.2.4 Image

One final reason that users have decided to make the conversion to OS/390 is that of image. This particular reason is little talked about because it is used the least. But, it is felt that it should at least be mentioned or acknowledged.

It has been felt by some users in the VSE community that VSE is the orphan of the S/390 operating systems, ranking behind OS/390 and VM/ESA. These concerns are partly justifiable and stem from the fact that VSE has often lacked functionality provided in OS/390 and VM/ESA. Even when VSE has provided such functionality it has not done so, at least from a user perspective, in a timely

Chapter 1. Why Customers Migrate 9

Page 33
Image 33
IBM OS/390 manual Image, Way Processor Support, Task Quantity, MVS Nucleus

OS/390 specifications

IBM OS/390, a versatile operating system, was a cornerstone in enterprise environments and played a pivotal role in mainframe computing. Released in the mid-1990s, OS/390 combined the strengths of IBM's MVS (Multiple Virtual Storage) with new features and enhancements, targeting scalability, reliability, and performance in demanding business applications.

One of the key features of OS/390 was its robust support for multiple users and processes. The system allowed thousands of concurrent users to access applications and data, ensuring high availability and minimizing downtime—a critical requirement for many large organizations. This scalability was supported through various enhancements in memory management and processor scheduling, enabling optimal resource allocation across diverse workloads.

OS/390 was known for its superior workload management capabilities. The Workload Manager (WLM) component allowed administrators to define service policies, specifying how system resources would be allocated according to the priority of tasks. This ensured that critical business processes received the necessary resources while less critical tasks were managed more flexibly.

Another significant characteristic of OS/390 was its commitment to security. The operating system provided comprehensive security features, including user authentication, data encryption, and auditing capabilities. This focus on security was vital for organizations handling sensitive data, ensuring compliance with regulations and safeguarding against unauthorized access.

OS/390 also supported advanced technologies that facilitated integration and development. The system included features like the IBM CICS (Customer Information Control System) for transaction processing and IMS (Information Management System) for database management. These technologies allowed organizations to build robust, high-performance applications tailored to specific business needs.

The ease of network integration was another strength of OS/390. With the advent of the Internet and global connectivity, OS/390 systems could easily interface with various network protocols, enabling businesses to operate in a connected world. This inclusion paved the way for many organizations to expand their capabilities and offer new services, driving digital transformation.

In conclusion, IBM OS/390 represented a significant advancement in mainframe technology, combining scalability, security, and robust workload management. Its rich feature set and support for critical enterprise applications solidified its role as a vital component of many organizations' IT infrastructures, ensuring they could meet their operational challenges head-on while supporting future growth. As technology continues to evolve, the legacy of OS/390 remains influential in the realm of computing.