Page 146 - Standard Handbook Of Petroleum & Natural Gas Engineering

Computer Applications 131

Table 1-30
Pascal Intrinsic Functions
ABS Returns the absolute value of an argument
ARCTAN Returns the arc tangent of an argument
CHR Returns a character in the position in the collating sequence given by the
argument
cos Returns the cosine of an argument
EOF Returns TRUE if the end of file has been reached, otherwise returns
FALSE
EXP Returns the exponential e raised to the power of the argument
LN Returns the natural logarithm of an argument
ODD Returns TRUE if an integer argument is odd, otherwise returns FALSE
ORD Returns the ordinal number of an argument
PRED Returns the predecessor to an ordinal argument
RESET Initializes an input file to accept values
REWRll -E Initializes an output file to accept values
ROUND Converts a real argument to an integer value by rounding
SIN Returns the sine of an argument
SQR Returns the square of an argument
SQRT Returns the square root of an argument
succ Returns the successor of an ordinal argument
TRUNC Converts a real argument to an integer value by truncating

System Software
System software is the connection between the user and the machine. It
provides management of the system resources and utilities which simplify
development of applications programs. Essential system software includes
1. Translators-Assemblers, interpreters, and/or compilers that translate
symbolic language into machine code.
2. Linkers and loaders-Linkers resolve references between program units and
allow access to system libraries; loaders place code into the main memory
locations from which it will be executed.
3. Operating systems-Manage hardware resources of the computer system.
Utili~ation may be of the batch method, in which program units, libraries,
and data are submitted to the system along with the job control language
statements needed to run the program. The operating system allocates the
central processing unit to one batch job at a time, according to a hier-
archical system. Time-sharing systems provide interactive sharing of resources
by many users. The system must interweave allocation of resources to users
and manage memory locations.
4. Utility programs-Simplify use by performing particular tasks for the
programmer, such as editing, debugging, etc.
5. File manager systems-Maintain files and handle data input to and output
from the files. Database management systems (DBMS) contain integrated sets
of files related by their use and provide uniform software interfaces for
accessing data. The essential relationships between records in the files may
be of several types, including sequential, associative, or hierarchical.
6. Telecommunications monitors-Supervise communications between remote
terminals and the central computer.