6947ch02.fm Draft Document for Review April 7, 2004 6:15 pm
56 IBM eServer zSeries 990 Technical Guide
Activation of logical partitions as well as dynamic storage reconfiguration will cause the
storage to be assigned to the type needed (CS or ES). This does not require a Power-on
Reset. No new software support is required to take advantage of this function.

Hardware System Area (HSA)

The Hardware System Area (HSA) is a non-addressable storage area that contains the CPC
Licensed Internal Code and configuration-dependent control blocks. The HSA size varies
according to:
򐂰The number of defined logical partitions.
򐂰If dynamic I/O is not enabled, the size and complexity of the system I/O configuration. The
HSA may hold the configuration information for up to 63 K devices per LCSS.
򐂰If dynamic I/O is enabled, the MAXDEV value specified in HCD or IOCP, in support of
dynamic I/O configuration.
2.2.6 Modes of operation
Figure 2-15 on page 57 shows the z990 modes of operation diagram, summarizing all
available mode combinations that are discussed in this section: z990 mode, image modes
and their processor types, operating system versions and releases, and architecture modes.
There is no special operating mode for the 64-bit z/Architecture mode, as the architecture
mode is not an attribute of the definable images operating mode.
The 64-bit operating systems are IPLed into 31-bit mode and, optionally, can change to 64- bit
mode during their initialization. It is up to the operating system to take advantage of the
addressing capabilities provided by the architectural mode.
The operating systems supported on z990 servers are shown in “Software support” on
page 133.
Note: The HSA is always allocated in the physical memory of Book 0.
Note: The z990 models only operate in Logically Partitioned Mode. ESA/390 TPF mode is
now only available as an image mode in a logical partition.