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Guest pages that must still be below 2G with z/VM 5.2

With z/VM 5.2, guest pages can remain in place in nearly all cases. There are some exceptions, which include:

  • Pages locked by the old 31-bit Diagnose x'98' interface
  • Certain vSIE cases involving virtual guest MP and the Systems Communication Area used by the real guest to manage communication between virtual guest CPUs
  • The communications area used by the Diagnose x'70' Time-of-Day Clock Accounting Interface

Layer 2 and Layer 3

The OSA-Express features and virtual switch can support two transport modes -- Layer 2 (Link Layer or MAC Layer) and Layer 3 (Network Layer). In Layer 2 mode, each port is referenced by its Media Access Control (MAC) address instead of by Internet Protocol (IP) address. Data is transported and delivered in Ethernet frames, providing the ability to handle protocol-independent traffic for both IP and non-IP, such as IPX, NetBIOS, or SNA.


QEBSM is active by default if the following conditions are true:

  • z/VM 5.2 is running
  • QEBSM is enabled on the hardware
  • the Linux guest supports QEBSM

If, for some reason, QEBSM needs to be deactivated, this can be accomplished by issuing the SET QIOAssist OFF command before Linux is started.

Absolute Maximum In-Use Virtual Storage for z/VM 5.2

This is the calculation of how much in-use virtual storage can be supported by a z/VM system if all real storage below 2 GB could be used for PGMBKs:

Total frames in 2G real storage: 2048*256 = 524288
Number of PGMBKs that fit into 2G real storage: 524288/2 = 262144
Equivalent in-use virtual storage: 262144 MB = 256 GB

In-use Virtual Storage Example for z/VM 5.3

This is an example calculation for the amount of in-use virtual storage that can be supported by a 256 GB z/VM 5.3 system when the average number of resident virtual pages in each in-use 1 MB virtual storage segment is 50:

Total frames in a 256G system: 256*1024*256 = 67108864
Frames required per in-use segment: 50 + 2 for the PGMBK = 52
Total in-use segments:  67108864/52 = 1290555
Total in-use virtual storage: 1290555 MB = 1260.3 GB = 1.23 TB


With z/VM 5.2 a maximum of 24 CPUs was supported for a single VM image. The 30-way measurement was conducted for comparison purposes, but is not a supported configuration.

placing the DEFINE CPU command in the directory

This makes use of the new user directory COMMAND statement that was added in z/VM 5.3. It can be used to specify CP commands that are to be executed after a virtual machine is logged on.

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