Enhancing system performance of 3270 or SLU 2 display devices

• Use preformatted screens. This is the most significant performance consideration for MFS when 3270 or SLU 2 display devices are used. Significant amounts of data are usually required to define fields and establish literals on a screen. These field definitions and literals do not always have to be transmitted. If the format on the device can be used, transmission time for remote terminals can be reduced up to 50 percent.
• Pad message output with nulls. The use of the FILL=NULL or PT option in the DPAGE statement reduces the amount of data transmitted to the device and the amount of processing required to format the output.
• Reduce mixed-mode operations. A mixed mode operation occurs when the selector light pen is used on an immediately detectable field and other fields on the device are modified. The mixed mode operation requires multiple I/O operations that increase response time, line utilization, and processing time. In addition, the resulting message contains the same data as would be produced by the enter key except for the indication that the selector pen was used.
• Use paging requests. Where application design permits, the PA1 (program access key 1) page advance facility should be used instead of operator entry of a logical page request. The PA1 facility requires less operator action and less communication line time, and does not require input editing before page request processing.
• Define the length of a literal DFLD followed by a nonliteral DFLD to include space between the last significant literal character and the position preceding the attribute position of the nonliteral field. This action can reduce block size and character transmission but should only be considered when the separating space is between two and five characters.
• Increase the length of DFLDs with the PROTECT attribute. When a nonliteral DFLD is defined with the PROTECT attribute, separated from the next device field by two or more blanks, and is expected to receive output data, consider increasing its length. The output data can originate from an application program, a /FORMAT command, or an MFLD literal. Multiple MODs can be used to map message data to the DFLD. Increasing DFLD length should reduce character transmission unless character fill (FILL=C' ') is specified. Specifying FILL=C' ' is not recommended.
• Minimize the use of the CLEAR key. Advise terminal operators not to use the CLEAR key unnecessarily. In addition, explain to terminal operators the proper use of other function keys such as the ERASE INPUT and ERASE EOF.

  Design screen formats with the objective of minimizing the use of the CLEAR key. Allow simple input from a formatted screen. To provide for this capability, establish the same device field location of all formatted screens as the standard device field for simple input. Enforce this standard for all format definitions.

  Decreasing CLEAR key usage can improve response time and use communication lines more effectively.

3270 or SLU 2 devices with large screens

If pages are combined for display on large screens, operator paging is reduced proportionally to the reduction of number of pages. If the OUTBUF keyword of the IMS system definition TERMINAL macro or ETO logon descriptor cannot specify the amount of data for an entire page, more than one VTAM® SEND is required to send the page.