Blank compression for line data

The Blank compression parameter in the Printer Inventory (see Blank compression) or the COMPRESS parameter in the PRINTDEV statement (see COMPRESS) provides a data compression function for line data. In line data that contains more than five contiguous blanks, PSF compresses the blanks to a single blank, plus control information for the printer to use in extracting the blanks.

Blank compression is most likely to improve printer throughput when a printer and the jobs being printed have the following characteristics:

The printer has a low-speed attachment.
Printer throughput is limited by the attachment.
The jobs are line data. Blank compression is not attempted for jobs of other types.
The line data contains a significant number of interior strings of more than five blanks.

Blank compression can be used for host-connected, channel-attached printers, for SNA-attached printers, and for TCP/IP-attached printers. However, IBM® does not recommend that you use it for host-connected, channel-attached printers, unless the attachment is the main performance bottleneck.

Note: Unless the printer and job characteristics are present, you might not see improvement in printer throughput. Increased processor cycles might be used to perform the blank compression, but if the line data does not contain significant interior blanks, the volume of data generated might not be decreased enough to affect the overall performance of the attachment and the printer.

For unformatted line data that contains fields of data whose placement is specified in a page definition, for example, blank compression might give little or no improvement in throughput. The data sent to the printer might not contain interior blanks, although the text on the spool contains many blanks.

The same might be true of formatted line data that has no interior strings of consecutive blanks, when JES has eliminated all trailing blanks because blank truncation was specified.

Because blank compression is an FSA parameter and affects all line data jobs sent to the printer, the system programmer should carefully check the characteristics of the jobs being printed, and the listed characteristics for the attachment and printer, before implementing the new parameter.