Control Blocks

The Tachyon Operating System creates and maintains a number of control blocks. In most cases the control blocks are at least partially filled in with reasonable information. In some cases an empty control block is allocated to allow programs to reference it without causing an addressing exception.

The SWA control blocks are always allocated below the 16 megabyte line. This allows older programs to access the SWA control blocks such as the JFCB, JFCX and SIOT.
 

Control Block Notes
ACEE
Accessor Environment Element
The job step ACEE is created.
APF Table
Authorized Program Facility Table
The static form of the APF table is built, based on the PROGxx.ini configuration files.
AMB
Access Method Block
One AMB is created for each open VSAM data or index component.
AMBL
Access Method Block List
One AMBL is created for each open VSAM ACB.
AMCBS
Access Method Control Block Structure
If the VSAM feature is licensed, the AMCBS is created and partially initialized, otherwise an empty AMBCS is built.
AMDSB
Access Method Data Statistics Block
One AMDSB is created for each open VSAM data or index component.
ARDB
Address Range Definition Block
One ARDB is created for each open VSAM data or index component.
ASCB
Address Space Control Block
One ASCB and its extensions (the ASSB and ASXB) are built for the active address space. The address space is for ASID 1.
ASTE
Address Space Second Table Entry
One ASTE is built for the active address space.
ASVT
Address Space Vector Table
The ASVT has only the entry for the ASCB of the active address space.
BUFC
Buffer Control Block
Buffers are allocated for each open VSAM ACB unless MACRF=UBF is specified. The BUFC control blocks are not compatible with those built by z/OS.
BUFCB
Buffer Pool Control Block
A buffer pool is allocated for QSAM data sets as they are opened.
CDE
Contents Directory Entry
A CDE and the associated Extent List (XTLST) is built for each non-LPA module loaded via the LINK(X), LOAD or XCTL(X) services.
CIB
Command Input Buffer
A CIB is allocated for each MODIFY or STOP operator command entered.
CICB
Compatibility Interface Control Block
A CICB is allocated for each BSAM and QSAM DCB opened for a subsystem data set.
CSD
Common System Data
The CSD is created.
CSCB
Command Scheduling Control Block
One CSCB is built for the active job. The CSCB extension (CSCX) is also created.
CVT
Communications Vector Table
The CVT and its extensions (CVTVSTGX, CVTXTNT1, CVTXTNT2, SCVT and ECVT) are created. The CVT and ECVT are initialized based on the IEASYSxx.ini BCP parameter.
DCB
Data Control Block
The Link List and JOBLIB/STEPLIB DCBs are created.
DCQ
Device Class Queue
The DCQ is created and the DASD queue is initialized.
DDIB
Data Definition Information Block
A DDIB is created for all data sets in the active job step with an associated DD PATH.
DEB
Data Extent Block
The DEB and the DEB extension are created for each open DCB.
DFA
Data Facilities Area
The DFA is initialized based on the IEASYSxx.ini DFP parameter. An empty Data Facilities Vector Table (DFVT) is also allocated.
DSAB
Data Set Attributes Block
A DSAB is created for each DD statement in the active job step.
DUCT
Dispatchable Unit Control Table
An empty DUCT is allocated.
DVCT
Device Characteristics Table
The DVCT is created and fully initialized.
EPIE
Extended Program Interruption Element
An EPIE is allocated by the SPIE/ESPIE service.
IOB
Input / Output Block
When a BSAM or BPAM DCB is opened, a partial IOB is built for each of the number of channel programs (NCP) requested.
JCT
Job Control Table
The JCT, its extension (the JCTX), its Account Control Table (ACT) and the Job Management Record (JMR) are created for the active job.
JESCT
Job Entry Subsystem Communication Table
The JESCT and the JESCT Pagable Extension (JESPEXT) are created. However, no subsystems are supported.
JFCB
Job File Control Block
A JFCB is created for every DD statement in the active step. The Job File Control Block Extension (JFCE) may also be created.
JSAB
Job Scheduler Address Space Control Block
One JSAB is built for the active job.
JSCB
Job Step Control Block
One JSCB is built for the active job step.
LCCA and LCCAVT
Logical Configuration Communication Area
One empty LCCA is chained off of the LCCAVT.
LDA
Local Data Area
The LDA is built for the active job step and contains the region size information.
LLE
Load List Entry
One LLE is built for each module loaded via the LOAD service.
LLT
Link List Table
The LLT, its extension (the LLTX) and the Dynamic LNKLST Control Block (DLCB) are built, based on the LNKLSTxx.ini configuration files.
LPAT
Link Pack Area Table
The LPAT is built, based on the LPALSTxx.ini configuration files.
LPDE
Link Pack Directory Entry
One LPDE is built for each module found in the data sets specified in the LPALSTxx.ini configuration files, forming the Pagable Link Pack Directory.
MPL
MVS Assist Parameter List
The SVC Table pointer in the MPL is initialized.
NUCMAP
Nucleus Map
The nucleus map is created and initialized with the Tachyon Operating System nucleus module and SVC routines.
OAPB, OASB, OTCB,
PPSD, PRLI and THLI
USS Control Blocks
These control blocks are allocated and initialized once the process is “dubbed” by invoking one of the UNIX System Services.
OCVT and OEXT
USS Common Vector Table and
USS Common External Control Block
If the IEASYSxx.ini OMVS parameter is set, the OCVT and OEXT areas are initialized.
PCCA and PCCAVT
Physical Configuration Communication Area
One PCCA is chained off of the PCCAVT. The CPU identification information is initialized from the LOADxx.ini CPUID parameter value or its default.
PIE
Program Interruption Element
A PIE is allocated by the SPIE/ESPIE service.
PLH
Place Holder
Place Holders are built for each open VSAM ACB. The PLH control blocks are not compatible with those built by z/OS.
PRB
Program Request Block
A PRB and the associated Extended Status Block (XSB) are built each time the LINK(X) or SYNCH(X) service is called.
RAX
RSM Address Space Block Extension
The RAX is built for the active job step and contains the MEMLIMIT value.
SAFV
System Authorization Facility Router Vector Table
An empty SAFV is allocated.
SCA
SPIE/ESPIE Control Area
The SCA is initialized for the active task.
SCB
STAE Control Block
One SCB is created for each active STAE, ESTAE or ESTAEX.
SCCB
Service Call Control Block
The SCCB is created.
SCT
Step Control Table
The SCT, its extension (the SCTX) and its Account Control Table (ACT) are created for the active job step.
SFT
System Function Table
The SFT is initialized with the PC numbers for the supported system routines.
SHID
System Host Identifier
The SHID is initialized with the information from the LOADxx.ini CPUID parameter value or its default.
SIOT
Step Input / Output Table
An SIOT is created for every DD statement in the active job step.
SVC Table The SVC Table is initialized with the entries for the supported SVCs and the routines in the IEASVCxx.ini configuration files. The ESR tables for SVCs 109, 116, 122 and 137 are also built.
SVRB
Supervisor Request Block
One SVRB and the associated Extended Status Block (XSB) are built each time a type 2, 3 or 4 SVC routine is called.
SVT
Supervisor Vector Table
An empty SVT is allocated.
SYMBT
Symbol Table
The static system symbol table is initialized with the entries from the IEASYMxx.ini configuration files.
TCAST
Terminal Control Address Space Table
An empty TCAST is allocated.
TCB
Task Control Block
One TCB and the associated Secondary Task Control Block (STCB) is built for the active task.
TIOT
Task Input / Output Table
The TIOT for the active job step is built from the DD statements.
UCB
Unit Control Block
A single UCB is created for a 3390 device with an address of X'0100' and volume serial of SYSRES. All DASD data sets are allocated to this unit.
VAT
Valid AMBL Table
One or more VAT entries are built as VSAM ACBs are opened.


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Last modified on May 17, 2005