Specifications

10
Using Callable System Routines
The OpenVMS operating system includes the following callable system routines
that perform various tasks:
• Run-time library (RTL) routines
• System services
• Utility routines
• OpenVMS RMS (hereafter referred to as RMS)
In this manual, a routine is a closed, ordered set of instructions that performs
one or more specific tasks. Every routine has an entry point (the routine name),
and optionally an argument list. Procedures and functions are specific types
of routines: a procedure is a routine that does not return a value, whereas a
function is a routine that returns a value by assigning that value to the function’s
identifier.
This chapter briefly describes the routines and references appropriate manuals
for more information.
10.1 Deciding Which Routines to Use
You can use system routines in programs to complete programming tasks such as:
• I/O operations
• Security procedures
• File manipulation
• Memory management
• Screen management
• Mathematics operations
• Event synchronization
• Utility usage
The sections that follow suggest sets of routines to use for each of these general
programming tasks.
10.1.1 I/O Operations
For I/O operations, you can use RMS, RTL routines, or system services. Use
RMS for device-independent I/O, when you want more control over file access.
Use RTL routines to get more functionality than language I/O statements. Use
system services for device-dependent I/O when you want more control over the
device. System services allow you to access devices not supported by RMS, to
perform I/O operations not supported by a particular language, and to increase
I/O performance.
10–1