6947ch01.fm Draft Document for Review April 7, 2004 6:15 pm
20 IBM eServer zSeries 990 Technical Guide

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

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).

OS/390 & z/OS

OS/390 R10 and z/OS 1.2 to z/OS 1.5 and later all provide Compatibility support. In addition,
z/OS 1.4, and z/OS 1.5 or later will have Exploitation support for up to 30 logical partitions
and four LCSSs. OS/390 supports both 31-bit and 64-bit modes, while z/OS 1.2 to z/OS 1.4
have the bimodal migration accommodation available for fallback to 31-bit mode for a period
of up to 6 months.
Exploitation support can be installed on any z/OS 1.4 system, regardless of the hardware it is
running on, but obviously uses functionality as provided by that hardware. The Exploitation
support is include on z/OS 1.5 and later releases.
When z/OS or OS/390 has only Compatibility support applied, it is limited to running in
LCSS0 and may not have an LPAR id greater than 'F'. In a z/OS only environment, if z/OS
does not have exploitation support, then it is limited to only 15 active logical partitions and up
to 256 CHPIDs. More partitions may be defined and may be physically installed, but they
cannot be used.
With Exploitation support on z/OS 1.4 or later, it is possible to fully exploit the z990
capabilities. It is possible to define up to 4 LCSS with up to 256 CHPIDs in each. Up to 30
logical partitions may be defined across the 4 LCSS. z/OS 1.5 has Exploitation support
delivered as part of the base function, but does not support 31-bit mode on z990.