Xerox 550 User Manual

1. XEROX 550 COMPUTER SYSTEM
INTRODUCTION
The Xerox 550 general-purpose, digital, computer system
accommodates a
variety of scientific, business, real-time,
and time-sharing applications. A system includes system
control, basic processor, I/O processor, and main memory
(up
to 256K words) with two ports. Each major system
element performs asynchronously
wi th respect to other
elements.
The basic system
can be readi Iy expanded. Memory access
paths can be increased from the basic two ports to a maxi-
mum of six ports. Input/output capabi I ity can be increased
by adding more
input/output processors (lOPs), device con-
trollers, and peripheral devices.
The basic processor (BP) has an extensive instruction set
that includes floating-point instructions.
The multiaccess memory units, with
interleaving, afford a
high level of system performance. Main memory
can be
expanded in
16K word increments to a maxi mum of 256K
words. Address
interleaving may be performed between
memory units of like
size. The number of ports to each
memory unit can be expanded to allow independent ac-
cess to memory by up to six "processor clusters" (i.e.,
functional groups).
Processor clusters are the grouping of two or more functions
{such as a basic processor,
an I/O processor, and inter-
faces} on a common bus. Clustering permits processors to
share common faci Ii ti es, e. g., buses and memory i nter-
faces. Therefore, the hardware is I ess redundant, hence
less complex, resulting in more reliabi lity at a lower cost.
There
are multiple combinations of functional groups from
which to
select.
Existing Sigma 5-9 programs may be run on the system.
The upward compati
bi I i ty of the comprehensi ve, mod-
ular software (assemblers, compilers, mathematical and
utility routines, and application packages) eliminates
reprogramming.
Features have been incorporated in this design
to enhance
overall system reliability, maintainability, and availability.
Centralized switches for system repartitioning may permit
faulty units, or
an entire subsystem, to be isolated for diag-
nosis or repair whi Ie the primary system continues operation.
Parity checking is performed on each byte of information
for most system interfaces and internal control signals. Most
failed instructions are automatically retried, and uninter-
rupted processing continues. The only apparent effect may
be an entry in the error log. In the event an error is irre-
coverable, there are error storage registers that return com-
plete data on the fault and the status of the system at
that point.
GENERAL CHARACTERISTICS
The following system features and characteristics permit
efficient operation in general-purpose, multiprocessor,
time-sharing,
real-time, and multiuse environments:
• Word-oriented memory (32-bit word plus parity bit
per byte) that can be addressed and altered as byte
(8-bit), halfword (2-byte), word (4-byte), and double-
word (8-byte) quantities.
• Memory expandable to 256K words (K == 1024) in mod-
ular units of
16K words each.
• Indirect addressing with or without postindexing.
• Displacement index registers, automatically self-
adjusting for all data sizes.
• Immediate operand instructions for greater storage
efficiency and increased speed.
• Four blocks of 16 general-purpose registers for address-
ing, indexing, and accumulating. Multiple registers
permit rapid
context switching.
• Hardware memory mapping, which virtually eliminates
memory fragmentation and provides dynamic program
relocation.
• Memory access protection for system aOO informaTion
security
and protection.
• Memory write protection within memory units to prevent
inadvertent destruction of critical areas of memory from
any processor cluster.
• Watchdog timer to assure nonstop operation.
• Real-time priority interrupt system with automatic iden-
tification and priority assignment, fast response time,
and 14 internal and up to 48 external levels that can
be individually armed, enabled, and triggered by
program
control.
• Instructions with long execution times can be interrupted.
• Automatic traps for error or fault conditions, with
masking
capability and maximum recoverability, under
program
control.
• Power fail-safe for automatic shutdown and resumption
of processing in
event of power fai lure.
• Multiple interval timers with a choice of resolutions
for independent ti
me bases.
• Privileged instruction logic for program integrity in
multiuse environments.
Xerox
550 Computer System

Xerox 550 Specifications

General

Brand	Xerox
Model	550
Category	Printer
Language	English