SAS Companion for UNIX Environments

Reading and Writing Binary Data

Different computers store numeric binary data in different forms. Hewlett-Packard, SUN, and RS/6000 store bytes in one order. IBM-compatible microcomputers and Compaq Tru64 UNIX (formerly Compaq's DIGITAL UNIX), which are all Intel-based UNIX systems, store bytes in a different order, called byte-reversed.

Binary data stored in one order cannot be read by a computer that stores binary data in the other order. When you are designing SAS applications, try to anticipate how your data will be read and choose your formats and informats accordingly.

The SAS System provides two sets of informats and formats for handling binary data:

The IBw.d, PDw.d, PIBw.d, and RBw.d. informats and formats read and write data in native mode, that is, using the byte-ordering system that is standard for the machine.
The S370FIBw.d, S370FPDw.d, S370FPIBw.d, and S370FRBw.d informats and formats force the data to be read and written according to the IBM 370 standard, regardless of the native mode of the machine. These informats and formats allow you to write SAS programs that can be run in any SAS environment, regardless of how numeric data is stored.

If a SAS program that reads and writes binary data runs on only one type of machine, you can use the native mode informats and formats. However, if you want to write SAS programs that can be run on multiple machines using different storage systems for numeric data, use the S370 formats and informats, which exist for that purpose.

For example, suppose you have a program that writes data with the PIBw.d format. You execute the program on a microcomputer so the data is stored in byte-reversed mode. Then you run another SAS program on the microcomputer that uses the PIBw.d informat to read the data. The data is read correctly because both the programs are run on the microcomputer, using byte-reversed mode. However, you cannot upload the data to a Hewlett-Packard 9000-series machine and read it correctly, because it is stored in a form native to the microcomputer but foreign to the Hewlett-Packard 9000. To avoid this problem, use the S370FPIBw.d format to write the data; even on the microcomputer, this causes the data to be stored in IBM 370 mode. Then read the data using the S370FPIBw.d informat. Regardless of which type of machine you use when reading the data, it is read correctly.

For more information on all of the informats and formats, refer to SAS Language Reference: Dictionary.

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