Abstract: An access control apparatus in a computer system for controlling access to an ALB. A host ALBID register and a guest ALBID register is provided for storing a host and a guest ALB identifier (ALBID) and a host and a guest ALBID validity indicator. Control State Software generates and stores the host and guest ALBIDs in the host and guest ALBID registers and marks valid the host and guest ALBID validity indicator whenever a host or guest mode is initiated or a logical purge is requested by a logical processor and for storing the host or guest ALBID stored in the host and guest ALBID registers when an ALB entry is made in the ALB by a logical processor.

Abstract: In a computer system including an interrupt processor for interrupting a program being processed by the computer system, a sub-system for processing interrupt requests to the interrupt processor. The sub-system comprises hardware circuit for generating hardware interrupt requests and control circuit for implementing control software where the control software causing software interrupt requests to be generated by said control circuit. An interrupt register stores and identifies both the hardware and software interrupt requests. A selection circuit selects and sends one of said stored interrupt request stored in the interrupt register to the interrupt processor for processing. The control circuit, under control of the control software, generates an end software interrupt requests for removing software interrupt request stored in the interrupt register such that software interrupt in the computer system can be generated and terminated under the control of the control software.

Abstract: A computer system having a chief system control program running in a real machine as a host where the host controls standard system control programs (SCP's) and controls virtual machines (Domains) called guests. Guests operate with interpretive execution as second-level guests. Control is transferred from a second-level guest to the guest SCP or to the chief SCP with only one control interception. Control is transferred directly between the second-level guest and the Chief SCP bypassing the first-level guest.