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(3)Hewlett-Packard HPGL <br />In general, hard-copy output for the CRDSS will be created in PostScript format because it is widely <br />supported and relatively simple to create. Many sites also have PostScript printers. Maps generated <br />by ARC/INFO can be plotted on many different output devices, including PostScript printers and <br />plotters that understand HPGL. <br />Data File Portability <br />A data file is portable if it can be read using exactly the same software on different platforms. For <br />example, if a program is written to display the results from a program, and then the display program <br />is ported to a different system, it should be able to read the output file as copied from the original <br />system. <br />ASCII files are usually very portable, and, if they are not, they can usually be easily edited. ASCII <br />files on UNIX systems have lines that end in a newline character, and files are terminated with and <br />end-of-file character (Ctrl-D). ASCII files on PCs (DOS and Microsoft Windows) have lines that <br />end with a carriage return followed by a newline character, and files are not terminated with a <br />specific character. File transfer programs and other software generally handle these differences <br />transparently (but a file transferred from UNIX to a PC will have a different file size because of the <br />extra carriage return characters). <br />Software that uses ASCII files for input and output is quite portable. However, because ASCII files <br />are formatted, they require more processing time to read/write. For example, if a 32-bit integer <br />needs to be written, it must first be converted to a format specified by the program (e.g., being <br />printed in a 4-character field). This is one reason that ASCII files have historically not been used by <br />some programs. <br />Binary files are those that contain data representations that are not easily readable. Such files often <br />contain extended characters and may not use ASCII characters. Binary files are written in a way that <br />can be easily mapped to computer memory. For example, rather than writing an integer in a 4- <br />character field, a 32-bit representation of the integer is written to the file in a format that is most <br />easily used by the computer. FORTRAN also supports a direct access file format that consists of <br />records of a constant length. <br />Binary files are often used for temporary files because they can be written and read more quickly <br />than ASCII files. Direct access FORTRAN files are often used for database-oriented operations <br />because a record can be read by specifying the record number (the record can be easily located <br />because all of the records have a fixed length). <br />Binary files are not generally portable because they are stored differently on different machines. For <br />example, machines can store information differently in memory. Some machines store the most- <br />significant bit of data on the left, and some machines store the most-significant bit of data on the <br />right. Consequently, reading a binary file from a "reverse" machine may scramble the data values. <br />Direct access FORTRAN files are also stored differently on different machines. Because the record <br />length for such files is not readily available from the system, the record length must be stored in the <br />file. Some systems (compilers) store the value once at the beginning of the file. Some store the <br />4 <br />A275 05.10.94 1.05-28 Malers <br />