File Copying Formats

Transparent Format

When files are copied from a source file node that is the same type of computer as the target file node (for example, if they are both HP 3000s or HP 9000s), the files are copied using a format called Transparent Format. Transparent Format does not alter a file's attributes, but simply copies the file. It should be used when you want a low-overhead, maximum-speed file copy process between systems of the same type.

Interchange Format

When two computers are of different types (for example, one is an HP 9000 running a release prior to HP-UX 10.0 and one is an HP 3000), files copied from one to the other must be converted to Interchange Format (Figure 5-2 “Interchange Format”). Interchange Format consists of a set of attributes that describe a file in a standard way so that it can be understood by any NS system. Interchange Format is invoked by default whenever you use NFT to copy a file residing on one type of system to a system of another type. You can also use a DSCOPY command option (INT) to explicitly specify that a file be converted to Interchange Format. In addition, several options automatically invoke Interchange Format. These options are described in the DSCOPY syntax description later in this chapter.

Figure 5-2 Interchange Format

When a file is copied using Interchange Format, it is translated into Interchange Format at the source system before it is copied to the target system. At the target system, it is mapped from Interchange Format into the target system's file format. Interchange Format's standard file attributes enable the target computer to map the source file into a target file with attributes that match the source file's as closely as possible.

You can use the options that invoke Interchange Format to give a target file a different set of attributes from those that characterized the source file from which it was copied, even if the files are being transferred between computer systems of the same type. For example, by copying a file composed of variable length records and using the FIX option, you can create a file containing the same information, but formatted into fixed-length records. Other options (described in detail later in this chapter) can be used to create duplicate files that differ from their source files in record size, length, type of data and other file characteristics.

Data Interpretation

Although the purpose of Interchange Format is to create an accessible target file on different kinds of systems, it does not ensure that the target file will be usable. This is because Interchange Format changes a file's attributes only; it does not perform data interpretation. Interchange Format can create an unusable target file if the target system has a different representation for the data present in the source file.

For example, if a file that contains floating point numbers is copied to a different kind of computer, there is no guarantee that the target node will be able to read the data as floating point. Consequently, the usability of your target files must be determined by the applications that use them.