IBM OS/390 User Manual
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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.
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.
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.
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.
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
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