Specifications

OpenVMS VAX Operating System, Version 5.5-2 SPD 25.01.37
The presence of vector support code in a system has lit-
tle affect on processes running in a scalar-only system,
or scalar processes running in a vector-present sys-
tem. If many processes must compete simultaneously
for vector processor resources in a system, the system
manager can maintain good performance by adjusting
system resources and process quotas as indicated in
the VMS documentation.
The VMS Operating System makes the services of the
vector processor available to system users by means
of a software abstract known as a capability. A system
manager can restrict the use of the vector processor to
users holding a particular identifier by associating an ac-
cess control list (ACL) entry with the CAPABILITY object
VECTOR.
The VAX Vector Instruction Emulation Facility (VVIEF) is
a standard feature of the VMS Operating System that al-
lows vectorized applications to be written and debugged
in a VAX system in which vector processors are not
available. VVIEF emulates the VAX vector processing
environment, including the non-privileged VAX vector in-
structions and the VMS vector system services, as de-
scribed in the VMS documentation. Use of VVIEF is
restricted to user mode code.
DECdtm Services
The DECdtm services embedded in the VMS Operating
System support fully distributed databases using a "two
phase commit" protocol. The DECdtm services pro-
vide the technology and features for distributed process-
ing, ensuring both transaction and database integrity
across multiple resource managers. Updates to dis-
tributed databases occur as a single "all or nothing" unit
of work, regardless of where the data physically resides.
This ensures consistency of distributed data.
DECdtm services allow applications to define "global
transactions" that may include calls to any of a number
of Digital data management products. Regardless of
the mix of data management products used, the global
transaction will either commit or abort. VMS is unique
in providing transaction processing functionality as base
operating system services.
DECdtm Features
• Embedded VMS system services support the DECtp
architecture, providing features and the technology
for distributed transaction processing.
• DECdtm allows multiple disjoint resources to be
updated atomically. These resources can be ei-
ther physically-disjointed (for example, on different
CPUs) or logically-disjointed (for example, in differ-
ent databases on the same CPU).
• DECdtm encourages robust application develop-
ment. Applications can be written to ensure that data
is never in an inconsistent state, even in the event of
system failures.
• As a VMS service, DECdtm can be called using any
Digital TP monitor (ACMS or DECintact) or database
product (DBMS, RDB, RMS). This is useful for appli-
cations using several database products.
Interprocess Communication
VMS provides a number of facilities for applications that
consist of multiple cooperating processes:
• Mailboxes are virtual devices that allow processes to
communicate with queued messages.
• Shared memory sections on a single processor or
a symmetrical multiprocessing (SMP) system permit
multiple processes to access shared address space
concurrently.
• Common event flags provide simple synchronization.
• The lock manager provides a more comprehensive
enqueue/dequeue facility with multi-level locks, val-
ues, and ASTs (Asynchronous System Traps).
Symmetric Multiprocessing
VMS provides symmetric multiprocessing (SMP) sup-
port for multiprocessing VAX systems. SMP is a form of
tightly coupled multiprocessing in which all processors
perform operations simultaneously. The processors can
perform operations in all VAX access modes (user, su-
pervisor, executive, and kernel).
VMS SMP configurations consist of multiple central pro-
cessing units executing code from a single shared mem-
ory address space. Users and processes share a single
copy of VMS. SMP also provides simultaneous shared
access to common data in global sections to all proces-
sors. VMS SMP dynamically balances the execution of
all processes across all available processors based on
process priority.
SMP support is an integral part of VMS and is provided
transparently to the user. Because an SMP system is a
single system entity, it is configured into a network and
VAXcluster systems as a single node.
VAXcluster Support
VAXcluster Software is a VMS System Integrated Prod-
uct (SIP) that is separately licensed. It provides a highly
integrated VMS computing environment distributed over
multiple VAX, VAX Workstation, and Micro/VAX CPUs.
This environment is called a VAXcluster system and may
contain up to 96 VAX CPUs.
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