Pathway/XM System Management Manual

Configuring Clients and Requesters
Compaq NonStop™ Pathway/XM System Management Manual—426761-001
5-20
Setting the DISPLAY-PAGES Parameter for Terminal
Devices
retry the write operations, so there is no need to back out the write. In contrast, a
key-sequenced file requires a transaction backout; otherwise, the transaction will fail
when the second write is attempted at the same location.
TMF Parameters and TMF Errors
If a TMF error occurs and makes normal operations impossible, do not attempt to
continue normal operations by setting the TMF parameter options to OFF. Setting these
options to OFF can have the following result:
•
A SCREEN COBOL program that uses ABORT-TRANSACTION or
RESTART-TRANSACTION to handle exceptions to normal program operation
only appears to execute; the TMF verbs have no effect.
•
With the SET SERVER TMF parameter set to ON and the SET TERM TMF or SET
PROGRAM TMF parameter set to OFF, the TCP makes checkpoint, retry, and
syncdepth decisions as if the TMF software were running. For example, the TCP
performs fewer checkpoints and opens servers with a sync depth of 0 instead of 1. In
this case, the TCP is not running in fault-tolerant mode, and a single CPU failure
can cause the application to fail.
Refer to the NonStop™ TM/MP Operations and Recovery Guide to determine how to
recover from the TMF error.
Setting the DISPLAY-PAGES Parameter for Terminal Devices
This subsection explains how to calculate the DISPLAY-PAGES parameter of the
SET TERM and SET PROGRAM statements.
Screen Caching
The DISPLAY-PAGES parameter specifies the depth of the terminal’s screen caching.
The Compaq 6520, 6530, and 6540 terminals and terminal emulators have screen
caching capability to increase performance. Performance is improved because screen
caching prevents a screen from being built a second time after the initial building of the
screen.
For example, when the first DISPLAY BASE operation for Screen A is executed, all the
terminal escape sequences needed to build the screen are written to the terminal. The
terminal stores the screen image and field definitions in its memory. When the next
DISPLAY BASE operation for Screen A is done, only a few escape sequences—enough
to display the stored screen—are written to the terminal. Such screen caching results in a
significant savings in terminal process time.
Terminal Memory Organization
The value of the DISPLAY-PAGES parameter affects how the terminal’s fixed amount
of RAM (random access memory) is used. RAM is divided into two separate areas: the
screen-image area and the field-attribute entries area. There is one screen-image area
associated with a screen definition and approximately two field-attribute entries
associated with each field definition. A field-attribute entry is an entry in a table that the