via an RPQ known as LLF (Limited Locking Facility) and later ELLF (extended). LLF and ELLF were both replaced by the Multipathing Lock Facility (MPLF). To run clustered (loosely coupled) z/TPF requires either MPLF in all disk control units or an alternative locking device called a Coupling Facility. Processor shared records Records that absolutely must be managed by a record locking process are those which are processor shared. In TPF, most record accesses are done by using record type and ordinal. Given a record type in the TPF system of 'FRED' with 100 records or ordinals, in a processor shared scheme, record type 'FRED' ordinal '5' would resolve to exactly the same file address on DASD — necessitating the use of a record locking mechanism. All processor shared records on a TPF system will be accessed via the same file address which will resolve to the same location. Processor unique records A processor unique record is one that is defined such that each processor expected to be in the loosely coupled complex has a record type of 'FRED' and perhaps 100 ordinals. However, if a user on any 2 or more processors examines the file address that record type 'FRED', ordinal '5' resolves to, they will note a different physical address is used. TPF attributes 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 (Computer room agent set — 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. There are several products available which connect to Prime CRAS and provide graphical interface functions to the TPF operator, such as TPF Operations Server. Graphical interfaces for end users, if desired, must be provided by external systems. Such systems perform