ASCB

The communication vector table (CVT) is kept in SQA. It contains a pointer to the ASVT (address space vector table) which is table the keep track of anll address spaces in the system.  ASVT entry contains the ASID and pointer to the ASCB. 

The size of ASVT is fixed at system generation. All address spaces are kept in ASVT except the master adddess space. The master ASID is 1 and is the first afdtrsss space created. The ASCB is hand crafted and not store in SQA

There is also a head and tail pointers that thread through the list of swapped in ASCB in dispatching priority order. This list is used by dispatcher to find the next AS to run. 

ASCB are kept in SQA and not swappable. ASCB contains information about the address space such as the address space ID, sequence number representing its position I the dispatcher queue, address pointer of the next ASCB file n the dispatcher queue. Whether the AS is swapped in or out, dispatching priority, EPS allocated, real storage frames allocated, number of ready TCB, number of active CPU this AS is on 

ASCB points to ASXB which contain information that f interest to individual AS. I’m t contusions j formation such as number of TCB in this AS, interrupt handler save area (IGSA) and SRB queue.   

ASXB is stored on LSQA and is swappable