Table of control block definitions

All of the control blocks are listed, and for each control block the acronyms, macros and descriptions are given.

Table 1. Control block definitions
Control block acronym Mapping macro Description
ADSC DBFADSC Area data set control block.
ALDS DBFAREA Area list data set.
AMPB IDLI DMBBASE=0 Access method prefix block. Contains information relative to a data set belonging to a database.
BALG DBFBALG Balancing group control block.
BFSP IDLIVSAM BFSP DL/I VSAM buffer handler pool prefix.
BFUS IDLIVSAM BFUS Subpool statistics block.
BHDR BHDR MSDB header.
BLOCKHDR DFSSPBLK Block header used by DFSPOOL Storage Manager.
BSPH IDLIVSAM BSPH Buffer subpool header block. Contains the number of buffers in this subpool.
BUFC IDLIVSAM BUFC Buffer control block. Contains pointers to buffers.
BUFENTRY DFSSPBLK Used by DFSPOOL Storage Manager to map the buffer size entries within the pool header.
CADSECT ICADSECT Communication area block. Contains the main dump formatter control block.
CBT DFSCBTS Control block. Represents storage pools (IPAGES) defined in DFSCBT00.
CCB ICLI CCBBASE=0 Conversational control block. Controls resources for conversational tasks.
CIB ICLI CIBBASE=0 Communication interface block. Contains information the device-dependent module needs to determine Message Format Service (MFS) operation.
CIRCA IPST IMS control region interregion communication area.
CLB ICLI CLBBASE=0 Communication line block. One exists for each communication line and for each node.
CLLE DFSCLLE Common Latch List Element. There is one block for each IMS ITASK, which is maintained in Key 7 storage.
CNT ICLI CNTBASE=0 Communication name table. One exists for each named logical terminal and component.
CPM (generated) Communication password matrix. Length varies based upon the number of passwords in the CPT.
CPT (generated) Communication password table. Defined by user.
CRB ICLI CRBBASE=0 Communication restart block.
CSAB OCO Callable Service Anchor Block. Used by IMS callable services modules.
CSVT DFSCSVT Callable Services Vector Table. Used by IMS callable services modules.
CTB ICLI CTBBASE=0 Communication terminal block. One exists for each terminal and for each subpool in the system.
CTM (generated) Communication terminal matrix. Length varies based upon the number of logical terminals (CNTs).
CTT ICLI CTTBASE=0 Communication terminal table. There is one for each different type of terminal, as well as different features.
CULE DFSCULE Common Use List Element. Used in latching by the IMS Use Manager.
CVB ICLI CVBBASE=0 Communication verb block. Reflects the relationship between the command message verbs and the passwords. It also reflects logical terminals associated with those commands.
CXB (generated) Communication extension block. Contains information that is required for control of a particular terminal. It is a logical extension of the CTB.
DBPCB IDLI DPCBASE=0 DL/I DB PCB.
DCB IDCBOSD Data communication block. Contains data pertinent to the current use of a data set.
DCB-EXT DFSDCBEX OSAM extension to the DCB.
DDIR IDLI DDRBASE=0 DMB directory entry. Contains an entry for each DMB known to IMS.
DFSAVEC DFSAVECT Dump formatter vector table.
DFSDOPTE DFSDOPTB Dump option entry block. It is the dump formatter CBTE request definition block.
DFSDPBFH DFSDBPFH Dump buffer pool blocks. Used for buffering offline dump storage.
DFSSBWO DFSSBWA Work area used by sequential buffering.
DMAC DBFDMAC DEDB area control block.
DMB IDLI DMBBASE=0 Data management block. There is one for each database descriptor entry described in the DDIR.
DMBSEC IDLI DMBBASE=0 Secondary list. There is one or more entry for each logically related segment and each index relationship.
DMCB DBFDMCB DEDB master control block.
DMHR DBFDMHR The buffer header for Fast Path. Describes the status of a particular buffer. The buffer headers (and buffers) are allocated in DBFCONT0. ESCDDMHR points to the first buffer and ESCDMBFN contains the number of headers. The relationship between buffer headers and buffers is fixed during IMS control region initialization.
DSEB DFSDSPDS Dynamic SAP Extension Block. Used to manage dynamic SAPs.
DSG IDLI DSGBASE=0 Data set group control block. There is typically one for each data set group referenced by the DBPCB.
DSPWRK1 IDSPWRK Dispatcher work area. There is one for each VS task (TCB) in an IMS environment.
ECB z/OS® macro Event control block. Describes the status of an event in an IMS environment.
ECNT DBFECNT Extended communications name table. (Fast Path)
EDSG DFSSBDSG Sequential buffering extension to the DSG.
EMHB DBFEMHB Expedited message handler block. (Fast Path)
EIB DFSPCA Partition Exit Interface Block Prefix.
EPCB DBFEPCB Extended PCB. (Fast Path)
EPF IEPF ECB prefix. Used to indicate the current status of the ECB and to connect the ECB to the appropriate SAP.
EPST DBFEPST Extended partition specification table. (Fast Path)
EQEL DFSEQEL Recoverable in-doubt structure queue elements. Identifies inaccessible data due to in-doubt status.
ESCD DBFESCD Extended system contents directory. (Fast Path)
ESRB DBFESRB Extended service request block. (Fast Path)
ESRT DBFESRT Expedited message handling region insert buffer. This buffer is a temporary save area for a message input. ESRTs are allocated in module DBFCONT0 by IMS control region initialization with a length equal to the largest terminal buffer defined. ESCDESRT points to the first ESRT. EPSTESRT points to a related ESRT. (Fast Path)
FAQE DFSSPBLK Free allocated queue element. Used by the DFSISMN0 Storage Manager to manage storage within a pool.
FDB IDLI FDBBASE=0 Field descriptor block.
FDT DBFMFDB Field description table.
FEDB ICLI FEDBBASE=0 Front end directory block. Stores global information about the front end switching facility.
FEIB ICLI FEIBBASE=0 Front end interface block. Contains data to allow the front end switching user exit to communicate with the transaction manager.
FRB DFSFRB Fast restart block.
GB IGLI GSAM data set control block. Contains information concerning the data set operation and pointers to other control blocks used for accessing records.
GBCB IGLI GSAM buffer control block. Contains the address of a unique buffer.
GLT IGLI GSAM load table. Provides all addresses of the GSAM load modules necessary for initialization.
GPT IGLI GSAM pointer table. Provides information required by resident and nonresident GSAM routines.
GQCB IGLI GSAM queues control block. Contains first and last pointers for the four queues of GSAM GBCBs used by GSAM BUFFIO.
HSSR DBFHSSR Holds area range information from SETR statements. HSSR is formatted in the offline dump.
HSSO DBFHSSO Holds image copy (IC) information from SETO statements.
HSSD DBFHSSD Holds information for the /DISPLAY HSSP command. HSSD is formatted in the offline dump.
HSSP DBFHSSPS Skeleton block. Temporarily holds HSSO/HSSR/HSSD information before scheduling.
IBFPRF IBFPRF Buffer prefix. There is one for each buffer described in each subpool used by the OSAM buffer manager.
IBPOOL IBPOOL OSAM buffer handler main buffer pool. Contains statistics and vectors to OSAM buffer subpools.
IDSC DBFIDSC IDSC is the image copy data set control block. It represents the Image Copy data set (IDS) the same way the area data set control block (ADSC) represents the area data set (ADS). IDSC also uses the same control block structure as the ADSC. An IDSC contains a description of the Image Copy data set. There are up to two IDSCs for each DEDB area with the Image Copy option. An IDSC is built dynamically at the first call to the area that is running as HSSP with the Image Copy option requested. The ISDC is released during Image Copy termination.

The IDSC control block is formatted in the offline dump.
IEEQE DFSIEQE In-doubt error queue element. Contains buffers of changed data (data in the in-doubt state).
ISPL ISUBPL OSAM buffer subpool. Provides a base for fixed length buffers and statistics about the buffers.
ISL DXRRLISL IRLM identified subsystem list. Contains the name of each subsystem and its status.
JCB IDLI JCBBASE=0 Job control block. There is one for each PCB. It contains level tables and segment blocks and a trace table of the previous calls.
LCB LCB Link control block. Represents the link for channel to channel, memory to memory, VTAM®, and binary synchronous connections in MSC.
LCD LCDSECT Log contents directory. Controls the interface between the logical and physical loggers in a DB/DC environment.
LCRE DFSLCRE Local current recovery element. Contains the sync point, checkpoint recovery information relative to each PST.
LEV IDLI LEVBASE=0 Level table. Consists of two parts: previous call and current call that is filled in by the call analyzer.
LIPARMS PARMBLK Language interface parameter block.
LLB ICLI CLBBASE=0 Link line block.
LTB ICLI CTBBASE=0 Link terminal block.
LXB LXB Link extension block.
MRMB DBFMRMB DEDB randomizing module block.
MSNB MSNB Message Control/Error exit interface block. Contains the block content before and after calling Message Control/Error exit DFSCMUX0 or during the interface processing.
PAC DFSPAC Database Resource Adapter (DRA) control block.
PAPL DFSPAPL DRA architected parameter list.
PARMLIST ICADSECT Dump formatter bulk print interface block.
PAT DFSPAT DRA thread control block.
PATE DFSPAT DRA thread entry control block.
PCA DFSPCA Partition Communication Area.
PCIB ICLI PCIBASE=0 Partition communication interface block.
PCPARMS PARMBLK Program control parameter block.
PCT DFSPCT Partition chaining table.
PDAE DFSPSEIB Partition Definition Area Prefix. Partition Definition Area Entry.
PDEX DFSDDIR Partition Directory Extension
PDIR IDLI PDRBASE=0 Program specification block directory. Contains entries for every program known to IMS.
PDL DFSPDL DRA dump parameter list.
PECA DFSPSEIB Partition Exit Communication Area.
PNT DFSPNT Partition Name Table.
POOLHDR DFSSPBLK Storage pool header used by the DFSPOOL storage manager to keep track of pool information.
PPRE DFSPPRE Standard IPAGE prefix mapping macro. Used for all IPAGEs created in IMS.
PQE DFSPQE DRA queuing element.
PSB IDLI PSBBASE=0 Program specification block. Relates to the application program and contains the PCBs associated with this PSB.
PSDB IDLI DMBBASE=0 Physical segment descriptor block. Describes each segment in the database.
PST IPST Partition specification table. There is one for each message or batch region; it contains a DECB for this partition, I/O terminal PCB, and parameters required for this region.
PTBWA DXRPTBWA IRLM pass-the-buck work area.
PTE DFSPNT Partition Table Entry.
PTK DFSPTK Partition Key Index Table.
PTX DFSPTX Partition Entry Index Table.
PXPARMS PARMBLK Parameter Anchor Block.
QCB IAPS SMBBASE=0 Queue control block.
QEL IAPS SMBBASE=0 Queue Element.
QMBA DFSQMGR Queue Manager Buffer Area.
RCPARMS IDLI PSTBASE=0 Region control parameter block.
RCTE DBFRCTE Routing code table entry.
RDLWA DXRRDLWA IRLM deadlock process work area. Contains information that must be communicated between the deadlock process modules.
RHB DXRRHB IRLM resource header block. Represents a resource.
RHT DXRRHT IRLM resource hash table. Provides a series of anchors for resource chains.
RLB DXRRLB IRLM resource lock block. Represents a request for a lock or a lock held on a resource.
RLCBT DXRRLCBT IRLM private area control block and table. Contains addresses of IRLM entry points.
RLMCB DXRRLMCB IRLM master control block. Contains branch entry addresses for all RLMREQ as well as queue anchors.
RLPL DXRRLPL IRLM request parameter list. This is the parameter list for all functional requests for the resource lock manager.
RLQD DXRRLQD IRLM query mapping macro. Maps IRLM control blocks/structures returned to the IMS invoker of QUERY.
RPL IDLIVSAM Request parameter list. Contains parameters passed to VSAM from IMS and the status returned to IMS from VSAM.
RPST DFSRPST Restart PST. Contains identifying information and characteristics of units of recovery.
RRE DFSRRE Residual recovery element. Contains sync point actions, such as Commit and Abort, relative to eachDb2 for z/OS connection out of a dependent region and is used for BMP restart processing, in-doubt processing, and restartable backout processing.
SAP ISAP Save area prefix. Relates to a save area set.
SBHE DFSSBHE Sequential buffering hash entry. Used to hash or anchor SDCB control blocks and to serialize the sequential buffer SDCB and SDSG control block subsystem chains. The SBHEs are part of the SBSCD.
SBPARMS DFSSBPAR Sequential buffering extension to PXPARMS.
SBPSS DFSSBPSS Small section of the SBPST that needs to be in CSA.
SBPST DFSSBPST Sequential buffering extension to the PST.
SBSCD DFSSBSCD Sequential buffering extension to the SCD. This extension contains the SBHE hash entries.
SBUE DFSSBBUF Sequential buffering buffer extension. There is one SBUE for each SBUF.
SBUF IBFPRF SBEXT=YES Sequential buffering buffer. One SBUF control block is used by sequential buffering to control each SB buffer. The SBUF control blocks of one SB buffer pool are contiguous in storage and are formatted as one entity.
SCAR DFSSBCAR Control block containing the interpreted data of one SBPARM control statement in the //DFSCTL file.
SCA1 DFSSBCAR Control block containing the uninterpreted data of one SBPARM control statement in the //DFSCTL file.
SCD ISCD System contents directory. Produced at system definition time, it contains major entry points for all facilities and system control information.
SDB IDLI SDBBASE=0 Segment descriptor block. Contains a logical description of the segment.
SDCB DFSSBDCB Sequential buffering extension to the DCB. Is for those DB data sets that are buffered by sequential buffering.
SDSG DFSSBDSG Sequential buffering extension to the DSG. Describes one I/O process. There is typically one SDSG control block for each data set group control block (DSG) that might potentially be buffered by sequential buffering.
SDWA IHASDWA System diagnostic work area.
SGT DFSPRSGT Segment table. Describes the segments used by the partial reorganization process. It is built during the DBD analysis phase. Its address is held in the common area field (COMASGT). The segment extension table (SGX) holds additional information about the segments.
SIDB DXRSIDB IRLM subsystem identification block. Used to identify each subsystem that relates to IRLM.
SIDX DFSSSIE Subsystem index entry.
SMB IAPS Scheduler message block. Related to a transaction.
SPQB ICLI SPQBASE=0 Subpool queue block. The SPQB represents the dynamic user for an ETO terminal and represents a set of static queues (CNTs) for a static ISC parallel session terminal.
SQPST ISQPST PST queue. Associated with the scheduler sequence queue.
SRAN DFSSBRAN Sequential range. Used in sequential buffering to describe a recently referenced set of consecutive DB blocks. Sequential buffering allocates one Sequential SRAN control block for each buffer set of each buffer pool. SB also allocates Random SRAN control blocks to each buffer pool. The Sequential SRANs and Random SRANs of one SB buffer pool are contiguous in storage and are formatted as one entity.
SSIB IEFJSSIB Subsystem identification block. Identifies the subsystem that requested services.
SSOB IEFJSSOB Subsystem options block. Used to request a particular function from the z/OS subsystem.
SSVP DFSSSVPL System Services Parameter List. Used by IMS System Macros for parameter lists for mailing out of line calls. There is one SSVP per ITASK, anchored off of the SAP.
TAB DFSTAB Transaction anchor block.
TCT DFSTAB Transaction class table. Used for queuing of messages in a priority sequence within a specified class.
TPPCB IDLI TPCBASE=0 Program communication block. There is one for each logical database being referenced by the application program.
UEHB UEHB User exit header block. Used for automated operator exit interface processing.
UXDT DFSUSRX User Exit Definition Table. Contains control information and user exit addresses for user exits managed by IMS standard user exit service.
UXRB DBRUXRB A unit of work (UOW) is represented by a UOW exclusive resource control block (UXRB), similar to the XCRB representing the CI. The UXRB contains information about the UOW (for example, Area, RBA) and is used for resolving potential UOW resource contention among dependent regions. Other UXRB fields include the lock token, number of associated XCRBs, the owning EPST, the update intent flag, and the PCB.

The UXRB control block is formatted in the offline dump.
VSI IDLIVSAM VSI VSAM sharing information control block. Controls VSAM sharing between subsystems.
WHB DXRWHB IRLM work unit block. Contains the anchor for all requests associated with that owner.
XCRB DBFXCRB Exclusive control resource block.
XMCA DFSXMC Cross-Memory Control-Address Spaces. There is one block for each IMS subsystem, which is maintained in Key 0 storage.
XMCI DFSXMC Cross Memory Control-ITASKs. There is one block for each IMS ITASK, which is maintained in Key 7 storage.
ZIB IZIB Zone initialization block. Used by the DFSISMN0 Storage Manager to keep track of a buffer obtained using ICREATE.