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device can be substituted for the device that will
ultimately be used.
A versatile, interactive, fully prompted system
command interpreter (SCI) allows direct
communication between the operating system and the
user. This powerful command interpreter is a major
convenience of the DXIO system.
The DXIO operating system is a modular
operating system that can be customized for each
customer's site. Customizing the operating system
improves the efficiency of resource utilization. An
interactive system-generation (sysgen) program is
supplied with the DXIO system to provide a fast and
convenient means of implementing the custom
system.
To protect Texas Instruments investment and its
customers' interests, the DXIO operating system is
only available on a licensed basis. The license
includes software updates for one year following
purchase with annual renewal subscriptions available.
(The software sUbscription service is also available to
users who allow their subscriptions to lapse and then
decide to update their systems.) The DXIO software
license also includes installation support (basic
system generation and verification) by a Texas
Instruments customer engineer. For additional
information, refer to the
990 Computer Family Price
List.
System Generation
The DX 10 operating system is a modular operating
system that can be customized for each
customer~s
site. Customizing the operating system has the
following advantages:
• Reduces disk- and memory-space requirements
(Eliminates unnecessary modules; such· asdeviee
service routines for equipment not included in the
customer's system)
• Increases operating speed (Eliminates code
sequences associated with unnecessary modules)
• Eliminates replication of device service routines
for multiple installations of a device type
• Adds device service routines for nonstandard
devices
• Adds user-defined operating-system service calls
• Adds user-defined extended operation (XOP)
processors
• Adjusts operating-system parameters for best
efficiency in a given installation.
The DXIO operating system is supplied to a
DS990 purchaser on a media that is compatible with
the system. Unless otherwise specified, the DXIO
system is supplied on a DSIO (5440-type) cartridge
8
for DS990 Model 4 Systems, on a DS25 disk pack
for DS990 Model 6 Systems, and on a DS50 disk
pack for DS990 Model 8 Systems.
The DXIO disk includes a standard DXlO
operating system that is compatible with the basic
DS990 configuration (including standard options).
The disk also includes a complete set of individual
DXIO component modules, which can be used in the
development of the custom DXIO system. An
interactive sysgen program builds the custom system
to user specifications. The sysgen program uses
prompting and tutorial displays to lead the user
through system generation. When system generation
is complete, a complete set of specifications is
displayed for user approval. At this point, the user
may back out, revise specifications, store the custom
system as an alternate system, back it up with an
additional copy, or activate it as the primary
operating system.
Program
~anagement
A multitasking operating system allocates the
resources of a single computer system to a number
of individual user programs in such a way that each
user appears to have exclusive control of the
computer system. Multitasking maximizes the
amount of useful work obtained from a given
amount of computer hardware.
User programs that operate under control of the
DX 1 0 operating system include a composite of tasks,
procedures, and overlays. Programs are installed and
stored in disk program files in memory-image form.
When a program is activated, its memory images are
rolled in from the disk and loaded into any available
memory areas. This specific activation of a program
is
call~da
task. M ultipletaskscanbe in memory at
any time. A scheduler in the DXIO operating system
allocates central-processing-unit (CPU) execution
time to the various tasks. Conceptually, every task is
in some partial state of completion with one task
actually executing while the others are either active
(in queue, ready to execute) or suspended (not ready
to execute).
The process of removing one task from execution
and putting another into execution is called
scheduling. Tasks scheduled by expiration of a time
limit are called time-shared tasks. Time-shared tasks
are queued at different priority levels. A
sophisticated scheduling algorithm allocates time
slices at the various priority levels; so no task is
locked out.
The architecture of the 990 computer family
supports multitasking software. The workspace
architecture allows rapid context switches with a
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