IBM OS/390 User Manual
1.2.2 Mergers/Acquisitions
As with corporate consolidations, mergers and acquisitions present an equal
number of challenges when having to incorporate the I/S organizations of the
companies involved. A challenge that clearly presents itself is when the
organizations involved run different host based operating systems (such as
OS/390 and VSE/ESA). In cases where it has been decided to merge the I/S
organizations rather than run as autonomous entities, the issue of which
operating system should become the single production operating system arises.
It is often decided that because of its robust/enhanced functionality the operating
system be OS/390. This, then, requires that the VSE subsystems and applications
be converted to OS/390.
number of challenges when having to incorporate the I/S organizations of the
companies involved. A challenge that clearly presents itself is when the
organizations involved run different host based operating systems (such as
OS/390 and VSE/ESA). In cases where it has been decided to merge the I/S
organizations rather than run as autonomous entities, the issue of which
operating system should become the single production operating system arises.
It is often decided that because of its robust/enhanced functionality the operating
system be OS/390. This, then, requires that the VSE subsystems and applications
be converted to OS/390.
1.2.3 Capacity Constraints
Users running DOS/VSE and/or VSE/SP encountered system capacity constraints
due to the architectural design limits imposed by VSE. The need for additional
system capacity and resources due to things such as application and end user
growth found many VSE users coming up against these constraints. OS/390
provided the much needed relief for users who found themselves in this
situation. Fortunately, with the introduction of VSE/ESA V1 many of these
constraints were removed.
due to the architectural design limits imposed by VSE. The need for additional
system capacity and resources due to things such as application and end user
growth found many VSE users coming up against these constraints. OS/390
provided the much needed relief for users who found themselves in this
situation. Fortunately, with the introduction of VSE/ESA V1 many of these
constraints were removed.
VSE users now find that many of the reasons, due to architectural limits, that
forced a conversion to OS/390 actually no longer exist. The following sections
describe some of these constraints in greater detail.
forced a conversion to OS/390 actually no longer exist. The following sections
describe some of these constraints in greater detail.
1.2.3.1 Virtual Storage
VSE/SP provided 24-bit addressing which supported 16 megabytes of virtual
storage. Users with the requirement for a large CICS partition, for example, were
forced to go to multiple CICS partitions when putting up a single large CICS
partition was not possible. This sometimes caused additional problems as it was
often difficult to split a single CICS application into multiple CICS partitions.
However, where possible, users chose to implement multiple CICS regions using
the CICS Multiple Region Option (MRO). Still, with the addition of multiple CICS
regions (MROs), comes the added expense of managing the MROs. And, as the
MROs numbers increase, you need system management tools, such as CICSPlex
System Manager for MVS/ESA (CICSPlex SM) to ease the system management
burden caused by multiple CICS systems.
storage. Users with the requirement for a large CICS partition, for example, were
forced to go to multiple CICS partitions when putting up a single large CICS
partition was not possible. This sometimes caused additional problems as it was
often difficult to split a single CICS application into multiple CICS partitions.
However, where possible, users chose to implement multiple CICS regions using
the CICS Multiple Region Option (MRO). Still, with the addition of multiple CICS
regions (MROs), comes the added expense of managing the MROs. And, as the
MROs numbers increase, you need system management tools, such as CICSPlex
System Manager for MVS/ESA (CICSPlex SM) to ease the system management
burden caused by multiple CICS systems.
MVS, or OS/390, provided users with virtual storage constraint relief through
31-bit addressing capabilities. However, some users found relief with virtual
address extensions (VAE) in VSE/SP V3. VSE/ESA V1 introduced 31-bit
addressing support. This now gives VSE users the ability to address up to 2GB of
virtual storage. Hence, it is now possible for VSE users with large CICS partition
requirements to have this requirement satisfied by VSE.
31-bit addressing capabilities. However, some users found relief with virtual
address extensions (VAE) in VSE/SP V3. VSE/ESA V1 introduced 31-bit
addressing support. This now gives VSE users the ability to address up to 2GB of
virtual storage. Hence, it is now possible for VSE users with large CICS partition
requirements to have this requirement satisfied by VSE.
Chapter 1. Why Customers Migrate
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