IBM 520Q User Manual

Chapter 2. Architecture and technical overview 

Combined with features designed into the POWER5 and POWER5+ processors, the POWER 
Hypervisor delivers functions that enable other system technologies, including 
Micro-Partitioning technology, virtualized processors, IEEE VLAN, compatible virtual switch, 
virtual SCSI adapters, and virtual consoles. The POWER Hypervisor is a basic component of 
system firmware that is always active, regardless of the system configuration.

The POWER Hypervisor provides the following functions:

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Provides an abstraction between the physical hardware resources and the logical 
partitions using them.

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Enforces partition integrity by providing a security layer between logical partitions.

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Controls the dispatch of virtual processors to physical processors. (For more information, 
see 2.12.2, “Logical, virtual, and physical processor mapping” on page 52.)

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Saves and restores all processor state information during logical processor context switch.

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Controls hardware I/O interrupt management facilities for logical partitions.

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Provides virtual LAN channels between physical partitions that help to reduce the need for 
physical Ethernet adapters for inter-partition communication.

The POWER Hypervisor is always active when the server is running, whether the server is 
partitioned or not, and also even when the server is not connected to the HMC. It requires 
memory to support the logical partitions on the server. The amount of memory required by the 
POWER Hypervisor firmware varies according to several factors. Factors influencing the 
POWER Hypervisor memory requirements include the following:

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Number of logical partitions

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Partition environments of the logical partitions

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Number of physical and virtual I/O devices used by the logical partitions

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Maximum memory values given to the logical partitions

The minimum amount of physical memory for each partition is 128 MB, but in most cases the 
actual requirements and recommendations are between 256 MB and 512 MB for AIX 5L, 
Red Hat Linux, and Novell SUSE Linux. Physical memory is assigned to partitions in 
increments of Logical Memory Block (LMB). For POWER5+ processor-based systems, LMB 
can be adjusted from 16 MB to 256 MB.

The POWER Hypervisor provides the following types of virtual I/O adapters:

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Virtual SCSI

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Virtual Ethernet

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Virtual (TTY) console

The POWER Hypervisor provides a virtual SCSI mechanism for virtualization of storage 
devices (a special logical partition to install the Virtual I/O Server is required to use this 
feature, see 2.12.3, “Virtual I/O Server” on page 54). The storage virtualization is 
accomplished using two paired adapters: a virtual SCSI server adapter and a virtual SCSI 

Note: Use the System Planning Tool to estimate the memory requirements of the POWER 
Hypervisor.

In AIX 5L V5.3, the 

command using the

 and 

 flags displays the POWER 

Hypervisor statistical data. Using the 

 flag adds summary POWER Hypervisor statistics 

to the default 

 output.