Editing Transaction Processing Facility (section)

===What TPF is not===
TPF is not a general-purpose operating system.  TPF's specialized role is to process transaction input messages, then return output messages on a 1:1 basis at extremely high volume with short maximum elapsed time limits.

TPF has no built-in graphical user interface functionality, and TPF has never offered direct graphical display facilities: to implement it on the host would be considered an unnecessary and potentially harmful diversion of real-time system resources.  TPF's user interface is command-line driven with simple text display terminals that scroll upward, and there are no mouse-driven cursors, windows, or icons on a TPF ''Prime CRAS''<ref>{{Cite web|url=https://www.ibm.com/support/knowledgecenter/SSB23S_1.1.0.15/gtpg3/gtpg3p.html?pos=2|title=z/TPF Glossary|last=IBM Corporation|website=[[IBM]] |date=19 Apr 2018|access-date=10 May 2018}}</ref> (''Computer room agent set'' &mdash; which is best thought of as the "operator's console").  Character messages are intended to be the mode of communications with human users. All work is accomplished via the use of the command line, similar to [[UNIX]] without [[X Window System|X]].  There are several products available which connect to Prime CRAS and provide graphical interface functions to the TPF operator, such as ''TPF Operations Server''.<ref>{{Cite web|url=https://www.ibm.com/support/knowledgecenter/SSB23S_1.1.0.15/com.ibm.tpfops.doc/kc_tos_welcome.html|title=IBM TPF Operations Server|last=IBM Corporation|website=[[IBM]] |date=19 April 2018|access-date=10 May 2018}}</ref> Graphical interfaces for end users, if desired, must be provided by external systems.  Such systems perform analysis on character content (see [[Screen scrape]]) and convert the message to/from the desired graphical form, depending on its context.

Being a specialized purpose operating system, TPF does not host a compiler/assembler, text editor, nor implement the concept of a desktop as one might expect to find in a general-purpose operating system.  TPF application source code is commonly stored in external systems, and likewise built "offline".  Starting with z/TPF 1.1, [[Linux]] is the supported build platform; executable programs intended for z/TPF operation must observe the [[Executable and Linkable Format|ELF]] format for s390x-ibm-linux.

Using TPF requires a knowledge of its ''<u>Command Guide</u>''<ref>{{Cite web|url=https://www.ibm.com/support/knowledgecenter/SSB23S_1.1.0.15/gtpo1/hfmsgs.html|title=z/TPF Operations Command Guide|last=IBM Corporation|website=[[IBM]] |date=29 January 2019 }}</ref> since there is no support for an online command "directory" or "man"/help facility to which users might be accustomed.  Commands created and shipped by IBM for the system administration of TPF are called "functional messages"—commonly referred to as "''Z-messages''", as they are all prefixed with the letter "Z".  Other letters are reserved so that customers may write their own commands.

TPF implements debugging in a distributed client-server mode, which is necessary because of the system's headless, multi-processing nature: pausing the entire system in order to trap a single task would be highly counterproductive.  Debugger packages have been developed by third party vendors who took very different approaches to the "break/continue" operations required at the TPF host, implementing unique communications protocols used in traffic between the human developer running the debugger client and the server-side debug controller, as well as the form and function of debugger program operations at the client side.  Two examples of third party debugger packages are ''Step by Step Trace'' from Bedford Associates<ref>{{cite web|last=Bedford Associates|title=Bedford Associates, Inc.|url=http://www.bedfordit.com/|access-date=October 17, 2012}}</ref> and ''CMSTPF'', ''TPF/GI'', and ''zTPFGI'', all from TPF Software, Inc.<ref>{{cite web|last=TPF Software|title=TPF Software, Inc.|url=http://www.tpfsoftware.com/|access-date=October 17, 2012}}</ref>  Neither package is wholly compatible with the other, nor with IBM's own offering.  IBM's debugging client offering is packaged in an [[Integrated development environment|IDE]] called ''IBM TPF Toolkit''.<ref>{{Cite web|url=https://www.ibm.com/us-en/marketplace/ibm-tpf-toolkit|title=IBM TPF Toolkit Overview|last=IBM Corporation|website=[[IBM]] |date=Dec 2017|access-date=10 May 2018}}</ref>