z/OS Control Block Information


In z/OS control blocks are used to manage the work and resources of the system. They are represented internally as areas containing specific information pertaining to events, activity and status occurring within the infrastructure’s operation. Control blocks are usually chain to one another and can span many areas of an operating system’s internal structure. Knowledge of control blocks are useful in finding out information about the system.

Control Block Access

To access a control block you need you need to know:

  1. The address of another control block containing a pointer to the control block you want.
  2. Where in the second control block that pointer is held.

Below you find a table with z/OS control blocks and their associated addresses. A good starting point is the Communications Vector Table (CVT). Its address is always held at offset 16 (Hex 10) in the Prefix System Area (PSA) and the PSA can always be found at virtual address zero.

Control block Block address Block description
<LINK 152>ACEE</link> ASXB+X'C8' Accessor Environment Element
ACEX ACEE+X'98' ACEE Extension (current)
APHT CSVT+X'0C'+X'08' APF List
<LINK 153>ASCB</link> <LINK 148>PSA</link>+X'224' Address Space Control Block
ASCBJBNI <LINK 153>ASCB</link>+X'AC' ASCB (Current) Batch Jobname (or zero)
ASCBJBNS <LINK 153>ASCB</link>+X'B0' ASCB (Current) Start/Mount/Logon
ASMVT <LINK 154>CVT</LINK>+X'2C0' Auxiliary Storage Mgt Vector Table
ASSB <LINK 153>ASCB</link>+X'150' Ad Space Secondary Block (current)
ASVT <LINK 154>CVT</LINK>+X'22C' Address Space Vector Table
ASXB <LINK 153>ASCB</link>+X'6C' Address Space Extension Block
BASEA <LINK 154>CVT</LINK>+X'94' Master Scheduler Resident Data Area
BASEX BASEA+X'C8' Basea Extension
CAUB VAB+X'08' Common Area User Block (current)
CAUBS GDA+X'194' System CAUB
CCT RMCT+X'04' SRM CPU management Control Table
CDA IOVT+X'18' Configuration Data Area
CPMT CMCT+X'0C' Channel Path Measurement Table
CSCB <LINK 153>ASCB</link>+X'38' Command Scheduling Control Block
CSD <LINK 154>CVT</LINK>+X'294' Common System Data
CSVT ECVT+X'E4' Contents Supervisor Table
<LINK 154>CVT</LINK> X'10' Communication Vector Table
CVTEXT <LINK 154>CVT</LINK>+X'148' Communications Vector Table Extention
CVTFIX <LINK 154>CVT</LINK>-X'100' Communications Vector Table Prefix
DACA JESCT+X'78' Device allocation Communication Area
DFA <LINK 154>CVT</LINK>+X'4C0' Dfp Id Table
DFVT <LINK 154>CVT</LINK>+X'4C0'+X'2C'
DLCBC ECVT+X'88' Dynamic Linklist Ctl Blk (current)
DLCBU ASSB+X'EC' Dynamic Linklist Ctl Blk (user)
DMCT RMCT+X'B4' Domain Table
DPTB RCVT+X'2E8' Racf Dynamic Parse Table
DQE SPQAx Vsm Descriptor Queue Element (One Of Zillions)
DSDT RCVT+X'E0' RACF Data Set Descriptor Table
ECVT <LINK 154>CVT</LINK>+X'8C' Extended CVT
EDT DACA+X'60' Eligible device table
EDT1 EDTL+X'10' First EDT
EDT2 EDTL+X'14' Second EDT
EDTL DACA+X'60' EDT list
GDA <LINK 154>CVT</LINK>+X'230' Global Data Area
GVT <LINK 154>CVT</LINK>+X'1B0' GRS Vector table
HID <LINK 154>CVT</LINK>+X'42C' CPU Information Iosdshid
ICT RMCT+X'08' I/O Management Control Table
IOCOM <LINK 154>CVT</LINK>+X'7C' I/O Communication area
IOVT IOCOM+X'D0' IOS Vector Table
IPA ECVT+X'188' Initialization Parameter Area
<LINK 150>JCT</LINK> <LINK 151>JSCB</LINK>+X'104' Job Control Table
JESCT <LINK 154>CVT</LINK>+X'128' JES Communication Table
<LINK 151>JSCB</LINK> <LINK 149>TCB</LINK>+X'B5' Job/Step Control Block
JSCBACT <LINK 151>JSCB</LINK>+X'15C' Active Job/Step Control Block
JSTCB <LINK 149>TCB</LINK>+X'7C' Job Step Tcb
LCCA <LINK 148>PSA</link>+X'210' Logical Configuration Com Area
LCCAVT <LINK 154>CVT</LINK>+X'300' Lcca Vector Table
LDA <LINK 153>ASCB</link>+X'30' Local Data Area
LLE <LINK 149>TCB</LINK>+X'24' Last Load List Element
LLT <LINK 154>CVT</LINK>+X'4DC' Link List Table
LLTC DLCBC+X'10' Link List Table (current)
LLTU DLCBU+X'10' Link List Table (user)
LLTX CSVT+X'04' Link List Table Volumesxxx
LNKLST <LINK 154>CVT</LINK>+X'4DC' Link List Table
LPAQ <LINK 154>CVT</LINK>+X'BC' Lpa Cde List
LPAR STGS+X'48'+X'2EC' Lpar information
LPAT VSTGX+X'38' Link Pack Area Table
LSCT RMCT+X'3C' Logical Swap Control Table
LUV EDT+X'10'+X'1C'
MCT RMCT+X'0C' Storage Management Control Table
NUCMAP <LINK 154>CVT</LINK>+X'4B0' Nucleus Map
OUCB <LINK 153>ASCB</link>+X'90' Resources Manager User Cont Blk
OUSB ASXB+X'80' Resources Manager User Swappable Blk
OUXB <LINK 153>ASCB</link>+X'94' Resources Manager User Extension Blk
PCCA <LINK 148>PSA</link>+X'208' Physical Configuration Comm Area
PCCAVT <LINK 154>CVT</LINK>+X'2FC' PCCA Vector Table
PIT HCCT+X'4F0' Initiator List (Changes Frequently With Jes)
<LINK 148>PSA</link> 0. Prefixed Save Area
PSCB <LINK 151>JSCB</LINK>+X'108' TSO Protected Step Control Block
PVT <LINK 154>CVT</LINK>+X'164' RSM Page Vector Table
RAB <LINK 153>ASCB</link>+X'178' RSM Address Space Block
RAX <LINK 153>ASCB</link>+X'16C' RSM Add Space Block Extension
RB <LINK 149>TCB</LINK> Request blocks for this task
RCE <LINK 154>CVT</LINK>+X'490' RSM Control and Enumeration Area
RCT RMCT+X'E4' SRM Resource Control Table
RCVI RCVT+X'184' RACF Identity cache communication vector
RCVT <LINK 154>CVT</LINK>+X'3E0' RACF Communication Vector Table
RCVX RCVT+X'258' RACF Communication Vector Table Extension
RIT PVT+X'04' RSM Internal Table
RMCA RMCT+X'14' System Resource Manager Control Area
RMCT <LINK 154>CVT</LINK>+X'25C' System Resources Manager Ctrl Table
RMEX RMCT+X'28' SRM External Entry Poiny Descriptor Table
RTCT <LINK 154>CVT</LINK>+X'23C' Recovery/Termination Control Table
SCCB <LINK 154>CVT</LINK>+X'340' Service Call Control Block
SCTE WMCT+X'24' wlm srm
SCT <LINK 151>JSCB</LINK>+X'148' Step Control Table
SCTX SCT+X'44' Step Control Table Extension
SCVT <LINK 154>CVT</LINK>+X'C8' Secondary Communication Vector Table
SHDR <LINK 154>CVT</LINK>+X'250' SLIP Header
SFT <LINK 154>CVT</LINK>+X'304'
SMCA <LINK 154>CVT</LINK>+X'C4' System Management Facilities Control Table
SMCX SMCA+X'178' SMCA Extension
SPQA SPQE+X'08' VSM Subpool Queue Anchors
SPQE <LINK 149>TCB</LINK>+X'18' VSM Subpool Queue Element
SPT GDA+X'88' VSM Subpool Table
SSCT JESCT+X'18' Subsystem Communications Vector Table
SSCVT JESCT+X'18' Subsystem Communications Vector Table
SSIB JSCBACT+X'13C' Subsystem Identification Block
SSVT SSCT+X'10' Subsystem Vector Table
STCB <LINK 149>TCB</LINK>+X'138' Secondary Task Control Block (TCB)
STGS <LINK 154>CVT</LINK>+X'31C' Measurement Facility Control Block
SVCT SCVT+X'84' Svc table
SVCTAB2 SCVT+X'88' Svc Update Recording Table
SVRB <LINK 153>ASCB</link>+X'10'
SVT <LINK 154>CVT</LINK>+X'364' Supervisor Vector Table
<LINK 149>TCB</LINK> <LINK 148>PSA</link>+X'21C' Task Control Block
TCBFSA <LINK 149>TCB</LINK>+X'70' TCB First Save Area
TCT <LINK 149>TCB</LINK>+X'A4' System Management Facilities Timing Control Table
TCTSTOR TCT+X'08' TCT Storage Area
TIOT <LINK 149>TCB</LINK>+X'0C' Task Input/Output Table (current)
TOT <LINK 148>PSA</link>+X'7FC' System trace operand table (TOT)
TSB <LINK 153>ASCB</link>+X'3C' Terminal Status Block (current)
TSVT <LINK 154>CVT</LINK>+X'9C' TSO/E Vector Table
UCM <LINK 154>CVT</LINK>+X'64' Unit Control Module
ULUT IOVT+X'08' Ucb Lookup Table
VAB ASSB+X'F0' VSM Address space Block
VATLST DACA+X'0C' Volume Attributs List
VSTGX <LINK 154>CVT</LINK>+X'4AC' Virtual Storage Extension of CVT
WMCT RMCT+X'20' WMCT wlm srm
WMST RMCT+X'18' WMST wlm srm
XMD SVT+X'94' Cross_Memory Directory (in PCAUTH)
XMSE ASSB+X'48' Cross_Memory Control Block (current)
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