OpenVMS Alpha Galaxy Guide
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  2.3  OpenVMS Galaxy Components and Concepts

  To appreciate how OpenVMS Galaxy uses APMP to run
  multiple instances of OpenVMS in a single computer, it is
  important to understand this new computing model.

  The Galaxy Software Architecture on OpenVMS includes the
  following hardware and software components:

  Console

  The  console   on an OpenVMS system is comprised of an
  attached terminal and a firmware program that performs
  power-up self-tests, initializes hardware, initiates system
  booting, and performs I/O services during system booting
  and shutdown.  The console program also provides run-time
  services to the operating system for console terminal I/O, en-
  vironment variable retrieval, NVRAM (nonvolatile random
  access memory) saving, and other miscellaneous services.

  In an OpenVMS Galaxy computing environment, the console
  plays a critical role in partitioning hardware resources.  It
  maintains the permanent configuration in NVRAM and the
  running configuration in memory.  The console provides each
  instance of the OpenVMS operating system with a pointer to
  the running configuration data.

  Shared memory
  Memory is logically partitioned into private and shared sec-
  tions.  Each operating system instance has its own private
  memory; that is, no other instance maps those physical pages.
  Some of the shared memory is available for instances of

  OpenVMS to communicate with one another, and the rest of
  the shared memory is available for applications.

  The Galaxy Software Architecture is prepared for a nonuni-
  form memory access (NUMA) environment and, if neces-
  sary, will provide special services for such systems to achieve
  maximum application performance.

  CPUs

  In an OpenVMS Galaxy computing environment, CPUs can
  be reassigned between instances.

  I/O
  An OpenVMS Galaxy has a highly scalable I/O subsystem be-
  cause there are multiple, primary CPUs in the system-one
  for each instance.  Also, OpenVMS currently has features for
  distributing some I/O to secondary CPUs in an SMP system.

  Independent instances

  One or more OpenVMS instances can execute without shar-
  ing any resources in an OpenVMS Galaxy.  An OpenVMS
  instance that does not share resources is called an  indepen-
  dent instance   .

  An independent instance of OpenVMS does not participate in
  shared memory use.  Neither the base operating system nor
  its applications access shared memory.

  An OpenVMS Galaxy can consist solely of indepen-
  dent instances; such a system would resemble traditional
  mainframe-style partitioning.

  2.3.1  APMP Concepts

  Architecturally, APMP is based on an SMP hardware ar-
  chitecture.  It assumes that CPU, memory, and I/O have
  full connectivity within the machine and that the memory is
  cache coherent.  Each subsystem has full access to all other
  subsystems.

  As shown in   Figure 2-1  diagram, APMP then looks at the
  resources as if they were a pie.  The various resources (CPUs,
  private memory, shared memory, and I/O) are arranged
  as concentric bands within the pie in a specific hierarchy.
  Shared memory is at the center.

  APMP supports the ability to divide the pie into multiple
  slices, each of disparate size.  Each slice, regardless of size, has
  access to all of shared memory.  Furthermore, because soft-
  ware partitions the pie, you can vary the number and size of
  slices dynamically.

  In summary, each slice of the pie is a separate and complete
  instance of the operating system.  Each instance has some
  amount of dedicated private memory, a number of CPUs,
  and the necessary I/O. Each instance can see all of shared
  memory, which is where the application data resides.  System
  resources can be reassigned between the instances of the
  operating system without rebooting.

  2.3.2  Another Possible Picture
  Another way to look at the APMP computing model is to
  think about how the resources could be divided.

  The overall sense of the diagram is that the proportion
  by which one resource is divided between instances is the
  proportion by which each of the other resources must be
  divided.

  Some boxes would have varying proportions per instance.

                     Physical
                     Memory                 CPU                   I/O
                   +------+  -  -  -  -  -  -+------+  -  -  -  -  -  -+------+
                   |       |             |       |             |       |
      Instance  1   |   M1   |           |       |             |   I1   |
                   +______+              |       |             +______+
                   |       |\            |       |            /|       |
                   |       |  \          |       |           /  |       |
      Instance  2   |   M2   |   \       |   C1   |         /   |       |
                   |       |    \        |       |         /    |       |
                   +______+     \        |       |        /     |       |
                   |       |\     \       |       |       /      |       |

                   |       |  \     \      |       |      /       |       |
                   |       |   \     \     |       |     /     |       |
                   |       |    \     \    |       |    /      |   I2   |
                   |       |     \     \   |       |   /       |       |
                   |       |      \     \  |       |  /        |       |
                   |       |       \     \+______+/            |       |
                   |       |        \     |       |            |       |
      Instance  3   |   M3   |       \    |       |            |       |
                   |       |          \   |   C2   |           |       |
                   |       |           \  |       |            |       |
                   |       |            \+______+  -  -  -  -  -  -+______+
                   |       |             |       |             |       |
                   |       |             |       |             |       |
                   |       |             |   C3   |            |   I3   |
                   |       |             |       |             |       |
                   +------+  -  -  -  -  -  -+------+  -  -  -  -  -  -+------+
                   |   Shared  Memory                                  |

                   |                                                   |
                   +------+  -  -  -  -  -  -+------+  -  -  -  -  -  -+------+
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