Multiport Memory System; Manual Partitioning Capability; Multiprocessor Control Function; Shared Input/Output - Xerox 550 Reference Manual

MULTIPORT MEMORY SYSTEM
The system has growth capabi I i ty of up to 6 ports per
memory unit. A memory unit may contain 16K or 32K words.
This architecture allows flexibility in growth patterns
and provides high memory bandwidth, essential to multi-
processor systems.
MANUAL PARTITIONING CAPABILITY
Manual partitioning capability is afforded for all system
units. Thus, besides the primary advantage of increased
throughput, a secondary advantage of a multiprocessor
system is the "fail-soft" ability. Given a duplicate unit,
any unit can be partitioned by selectively disabling it from
the system buses. Depending on the type of failing unit,
the system will be operable, with some degree of degraded
performance. An alternate processor bus with dual system
capabilities can be provided.
MULTIPROCESSOR CONTROL FUNCTION
A multiprocessor control function is provided on all multi-
processor systems. This function provides these basic features:
1. Control of the External Direct Input/Output bus (Ex-
ternal 010), used for controlling system maintenance
and special purpose units such as analog to digital
converters.
2. Central control of system partitioning.
3. Centralized interrupt system, providing capability for
the operating system to use interrupts to schedule tasks
independently of the number of basic processors pres-
ent ina system.
4. Processor to processor communication via processor
buses.
SHARED INPUT/OUTPUT
In a multiprocessor system, any basic processor may direct
I/O actions to any I/O processor. Specifically, any basic
processor can issue an SIO, TIO, TOY, or HIO instruc-
tion to begin, test, or stop any I/O process. However,
the
II
end-action" sequence of the I/O process is directed
to one of the basi c processors in the system by the System
Control Processor. This feature (accomplished by setting
a pair of configuration control switches) allows dedicating
I/O end-action tasks to a single processor and avoids con-
flict resolution problems.
Multiprocessor Features 7