GitHubContribute in GitHub: Edit online

IBM Z Hypervisor as a Service (zHYPaaS) overview

The zHYPaaS host control program creates a virtual machine (VM) runtime environment for each guest operating system (OS) and can host many guests at the same time.

The IBM z/Architecture provides a means for the guest operating system to determine the available hardware facilities, including both actual and virtualized hardware. The hardware information can be obtained through the Store System Information (STSI), Store Facility List (STFL), Store Facility List Extended (STFLE), Store CPU ID (STIDP) instructions, or any related interfaces of the hypervisor and the guest operating system. However, some hardware facilities or features might not be available to the guest operating system because the zHYPaaS chose not to support them. In addition, zHYPaaS might hide or alter certain aspects of the underlying actual hardware. For more information about the hardware environment, see How to determine the hardware environment External link icon.

Understanding and determining when zHYPaaS is the host

zHYPaaS presents a STIDP environment code that indicates an alternate level 3 configuration and uses the STSI instruction to provide three levels of the machine configuration information, including the central processor complex (CPC), the logical partition (LPAR), and the virtual machine in which the guest operating system is running. Under the virtual machine environment, the STSI instruction returns a System-Information Block (SYSIB) 3.2.2 with the VM Control-Program Identifier, which can be used to identify that zHYPaaS is the host control program. Both the STIDP environment code and the STSI instruction must be used together to determine that zHYPaaS is the host.

STIDP instruction

zHYPaaS returns STIDP information as follows:

  • The STIDP environmental code is set to x’FD’ to indicate an alternate level 3 configuration.

  • Configuration Identification: Bit positions 8-31 contains six hexadecimal digits as described in the following order:

    • Two digits containing the LPAR user-partition identifier (UPID) that is assigned to the virtual server instance. It is the same value that is returned in the LPAR-number contained in STSI SYSIB 2.2.2. For more information, see STSI instruction.
    • Four digits are the rightmost 4 hex digits of the CPC sequence code. For more information about the sequence code, see STSI altered by zHYPaaS.
  • The Machine-Type Number in bit positions 32-47 matches a machine type related to the virtual server instance hardware profile that is selected. It represents the actual IBM Z hardware machine type of the IBM Z hardware, which the virtual server instance is running on.

STSI instruction

Typically, zHYPaaS is running in an LPAR on a machine with many other LPARs. In some environments, the STSI instruction might not alter the actual LPAR and CPC information. However, due to the nature of IBM Cloud, the zHYPaaS alters some values for the CPC, LPAR, and VM to make each virtual server instance appear to be running in its own LPAR and CPC. Therefore, the LPAR and CPC do not appear to have more resources than the VM.


The STSI VM information is unique to zHYPaaS virtual server instances and the key information is presented as follows:

  • The first token of the Control-Program Identifier is set to Extended Binary-Coded Decimal Interchange Code (EBCDIC) zHYPaaS and it ends at the first blank. Extra identification information might or might not be provided after the first token. The first token is sufficient to determine whether zHYPaaS is the host or not.
  • The Universally-Unique Identification (UUID) is unique for each virtual server instance.
  • The EBCDIC Virtual-Machine Name is set to the first 8 characters of the Extended Virtual Machine Name. The extended name must be used as the VM name is greater than 8 characters.
  • The EBCDIC Extended VM Virtual-Machine name is set to the cloud instance identifier (ID). The ID is static and persists for the lifecycle of the virtual server instance until that virtual server instance is deleted. Note: All lowercase letters are capitalized and the virtual server instance's ID can also be retrieved through the cloud provided instance details. For more information about how to retrieve the identifier based on different operating systems, see Retrieving the virtual server instance identifier External link icon.

STSI altered by zHYPaaS

For zHYPaaS, some STSI values are altered:

  • The Machine-Type Number matches a machine type related to the virtual server instance hardware profile that is selected. It represents the actual IBM Z hardware machine type of the IBM Z hardware, which the virtual server instance is running on.
  • The first character of the four-character Plant of Manufacture (POM) is set to EBCDIC character C. For zHYPaaS, the POM is set to C1 with trailing blanks, but the second character or the remaining 2 trailing blank characters might change in the future to denote specific attributes.
  • The Logical-CPU ID in SYSIB 2.2.1 and the Logical-Partition Number in SYSIB 2.2.2 are set to a virtual LPAR number that has no relationship with the actual LPAR that zHYPaaS is running in. The virtual LPAR number is not unique for each zHYPaaS instance even within the same CPC.
  • The EBCDIC CPC sequence code is unique for each virtual server instance. However, it has no relationship with the actual machine sequence code or actual CPU ID. The CPU ID that is retrieved from the STIDP instruction includes the rightmost 4 hex digits of the configuration-identification field.
  • The machine Model-Capacity Identifier is EBCDIC character A00.
  • The Model-Permanent-Capacity Identifier (P) and Model-Temporary-Capacity Identifier (T) are always equal to the Model-Capacity Identifier value.
  • The Model-Capacity Rating (CR) and other model capacity ratings are set to 0.

For more information, see z/Architecture Principles of Operation External link icon.