$JCT/JMR relationship

The MVS™ Job Management Record (JMR) is initialized as part of the JES2 $JCT when the $JCT is built by HASPRDR.

Additionally, the following information should help in the understanding of the $JCT and JMR relationship:

SMF documentation references to the Common Exit Parameter Area (CEPA) which is actually the MVS JMR.
During the Conversion, Execution, and Purge phases of JES2, the JMR is built by copying the JMR section of the JES2 $JCT into the MVS JMR and constructing the JMR extension.
At the end of the Conversion and Execution phases of JES2, the MVS JMR is copied back into the $JCT. Any alterations to the JMR is therefore checkpointed along the JES2 $JCT.
The CEPA User-Communication field (defined as JMRUCOM in the JMR) could be used to provide addressability to the JES2 $JCT for SMF exits.
There is a MVS Job Control Table (JCT). It's built by MVS and used during execution by MVS. and has nothing to do with the JES2 JCT.

The following table, Table 1, displays a side-by-side label comparison of the JMR (CEPA) and the JES2 $JCT/JMR areas.

Table 1. $JCT/JMR Definitions
$JCT Label	JMR Label	Length	Field Description
JCTJMRJN	JMRJOB	8 characters	8-character job name from JOB JCL statement
JCTRDRON	JMRENTRY	4 bytes	Time, in hundreds of second, on Input processor
JCTRDTON	JMREDATE	4 bytes	Date on Input processor in form of 00YYDDDF
JCTCPUID	JMRCPUID	4 bytes	SMF SYSID
JCTUSEID	JMRUSEID	8 characters	Initialized to blanks by JES2
JCTSTEP	JMRSTEP	1 byte	Current step number
JCTINDC	JMRINDC	1 byte	SMF options
JCTJTCC	JMRFLAG	1 byte	Job status indicator
JCTCLASS	JMRCLASS	1 byte	First byte of execution job class
JCTUCOM	JMRUCOM	4 bytes	User communication area - initialized to zeros by JES2
JCTUJVP	JMRUTLP	4 bytes	User time limit exit routine
JCTRDROF JCTRDTOF	JMRDRSTP	8 bytes	First word is time off input process and second word is date off input process
JCTJOBIN	JMRJOBIN	4 bytes	Job's SYSIN count
JCTRDR	JMRRDR	2 bytes	Reader device type and class
JCTJMOPT	JMROPT	1 byte	SMF option switches
(none)	(none)	1 byte	Reserved
JCXJCLA8	JMRCLAS8	8 characters	8 character jobclass
(none)	JMRJOBCORRELATOR	64 characters	JES job correlator for inclusion in SMF records