Guardian Application Conversion Guide

1 Introduction
096047 Tandem Computers Incorporated 1–1
Most TAL, COBOL85, C, or Pascal applications or Tandem Advanced Command
Language (TACL) programs written for the C-series operating system can run under
the D-series operating system without modification. However, to take advantage of
the higher limits of the D-series operating system, an application might need to be
converted as described in this manual.
Also, most applications written to run on TNS systems can run on TNS/R systems
without modification. However, modifications might be required in some programs,
particularly in privileged TAL programs. This manual also provides information
about converting applications to run on TNS/R systems.
This section introduces the D-series operating system and summarizes the differences
between the C-series and the D-series operating systems that affect an application
program. This section also provides an approach to converting an application and
discusses conversion options.
Why a New
Operating System?
Tandem designed the C-series operating system for earlier computer systems. Newer
systems such as the Cyclone system are faster and more sophisticated. Therefore,
when running a C-series operating system, newer computer systems sometimes
encounter these limitations:
CPUs are not used efficiently.
Newer Tandem systems execute instructions faster than older systems. When
running a C-series operating system, which supports only 256 concurrent
processes per CPU, a CPU in a newer system can become I/O bound (that is, all
processes are waiting for an I/O operation to finish). Sometimes the CPU becomes
idle and must wait before it can continue executing instructions.
I/O configurations are limited.
While earlier systems have only one I/O channel per CPU, newer systems allow a
maximum of four channels per CPU. Usually, each I/O device requires an I/O
process (IOP), which is a system process that controls the device. Increasing the
number of I/O devices in a system also requires an increase in the number of IOPs
that are running concurrently in a CPU. Thus, when running a C-series operating
system, which allows only 256 concurrent processes per CPU, a newer system
might not be able to support its maximum number of I/O devices.
The D-series operating system increases the number of concurrent processes per CPU
from 256 to an architectural limit of 65,534. The actual limit is at most 2500 and might
be less, depending on availability of segments, time-list elements (TLEs), and memory.
Increasing the number of concurrent processes per CPU:
Improves the efficiency of each CPU
Allows for more IOPs so that larger I/O configurations can be supported
The D-series operating system also supports larger I/O configurations by increasing
the software limits for the maximum number of: