Chapter 1. zSeries 990 overview 19
workloads; and batch jobs get resources as they are available. The strength of zSeries I/O
subsystem and I/O balancing capabilities are also key reasons for this platform’s excellent
support of batch workloads.
UNIX® System Services
UNIX System Services include shell functions, numerous utilities, and UNIX file systems.
Perhaps most significantly, what distinguished z/OS UNIX from other variants is that the
UNIX services were integrated into the z/OS base, not added as middleware or shipped as a
separate S/390 operating system. As a result, not only can UNIX applications be written for
zSeries, but they can also take advantage of z/OS facilities and zSeries hardware to obtain
true enterprise server qualities of service.
The importance of UNIX System Services is growing because most new applications and
middleware build upon them.
zSeries File System (zFS)
To meet the changing needs of new workloads, a different file system is available with
OS/390® R10 and beyond. This file system is complementary to the existing Hierarchical File
System (HFS), but provides enhanced performance and easier management for many
different file usage patterns often encountered with new workloads.
Linux on zSeries (and Linux for S/390)
Linux on zSeries offers a number of advantages compared to other platforms. First, it puts the
Linux applications close to the enterprise data and applications, thus reducing the chance for
bottlenecks. And since a Linux application runs in its own partition, with its own dedicated
resources, it does not impact the availability or security of the rest of the system.
A second advantage is the extremely reliable zSeries hardware, which can support up to 15
logical partitions on z900/z800 and up to 30 Linux logical partitions on z990—and thousands
of Linux images if Linux is run as a guest operating system under z/VM. Consolidation of
multiple Linux images on a single server can greatly simplify systems management.
With the large number of applications available in the open source community, many
customers will find Linux gives them a relatively low-cost way to deliver and integrate new
applications quickly. For others, Internet enablement may be quicker and easier when they
extend existing applications. Either way, zSeries support for the Application Framework for
e-business and Linux gives that choice and flexibility.
The choice of application source depends on a number of factors, including the source, the
required qualities of service, and the time allowed for development.
1.3.16 Software support
Here we discuss software support.
Compatibility and exploitation
Generally speaking, software support for the z990 comes in two steps: Compatibility support
and Exploitation support. However, there are variations specific to each operating system.
Compatibility support provides no additional functionality over and above a z900 or z800.
Compatibility only provides PTFs that allow the operating system to run on z990 or coexist in
a sysplex with z990.
Exploitation support provides the operating systems with the ability to take advantage of
greater than 15 logical partitions and multiple Logical Channel Subsystems (LCSS).

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