Guardian Application Conversion Guide

What Are the Differences?
Introduction
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I/O devices and named processes from 4,096 to 65,535 per system
I/O subdevices per device from 256 to a theoretical limit of 65,535 depending on
the subsystem
Opens per subdevice from 16 to a theoretical limit of 65,535, again depending on
the subsystem
Opens per disk volume from 4,096 to 32,767
Again, these values are the architectural limits. The actual limits depend on the
available resources of the system.
What Are the
Differences?
The major differences between the C-series operating system and the D-series
operating system that affect an application program are:
More concurrent processes per CPU
The D-series operating system allows more than 256 concurrent processes per
CPU; a C-series operating system allows a maximum of 256 processes per CPU.
New system procedures
New user-callable system procedures are available for converted applications in
order to support the extended system limits. These procedures use new naming
and error-return conventions.
New file-name format
The D-series file-name format for disk file names, device names, and process file
names is a variable-length string. The string length is specified as a separate
integer value.
New process identifiers
The D-series process file name is a variable-length string that replaces the C-series
process file name. The D-series process handle is a 20-byte structure that replaces
the C-series 4-word process ID (or CRTPID).
New system messages
New user-level system messages are available for converted applications to read
from $RECEIVE.
Improved performance for I/O operations
The D-series operating system can improve the performance of I/O operations by
directly transferring data between an application’s I/O buffers and the I/O device
without having to allocate an intermediate buffer in the application’s process file
segment (PFS).
New Distributed Systems Management (DSM) tokens
The Event Management Service (EMS) and the Subsystem Programmatic Interface
(SPI) have new tokens and filter functions for DSM applications.