Task Control Block
Encyclopedia
The Task Control Block is an instance of a Process control block
in an IBM System/360 architecture
and successors operating system environment.
Because of the complexities of the OS/360 and successors
control program dispatcher, a TCB does not strictly perform all the functions of a Process control block, although it performs most of these.
Rather, a TCB provides the anchor for a linked list of other, related request control blocks (RBs), the composite of which (i.e., the TCB plus the top-linked RB) performs the function of a Process control block.
The Program status word
may be stored in one control block (possibly a PRB, a Program Request Block), while the general purpose registers may be stored in the immediately preceding control block (an SVRB, Supervisor Call Request Block, an IRB, Interruption Request Block, or possibly the TCB itself), depending upon the particular context.
With the introduction of MVS/370 and successor systems, a whole new environment was introduced: the Service Request Block (SRB), which generally has a higher priority than any Task Control Block, and, indeed, which itself has two distinct priorities: a Global SRB (priority over all local address space SRBs and TCBs) and a Local SRB (priority over only the local address space TCBs); and MVS's dispatcher must manage all of these with absolute consistency across as many as two processors (MVS/370) and as many as sixteen processors (successor systems).
Process control block
Process Control Block is a data structure in the operating system kernel containing the information needed to manage a particular process...
in an IBM System/360 architecture
IBM System/360 architecture
The IBM System/360 architecture is the model independent architecture for the entire S/360 line of computers. The elements of the architecture are documented in the IBM System/360 Principles of Operation and the IBM System/360 I/O Interface Channel to Control Unit Original Equipment Manufacturers'...
and successors operating system environment.
Because of the complexities of the OS/360 and successors
OS/360 and successors
OS/360, officially known as IBM System/360 Operating System, was a batch processing operating system developed by IBM for their then-new System/360 mainframe computer, announced in 1964; it was heavily influenced by the earlier IBSYS/IBJOB and Input/Output Control System packages...
control program dispatcher, a TCB does not strictly perform all the functions of a Process control block, although it performs most of these.
Rather, a TCB provides the anchor for a linked list of other, related request control blocks (RBs), the composite of which (i.e., the TCB plus the top-linked RB) performs the function of a Process control block.
The Program status word
Program status word
The Program status word is an IBM System/360 architecture and successors control register which performs the function of a Status register in other architectures, and more....
may be stored in one control block (possibly a PRB, a Program Request Block), while the general purpose registers may be stored in the immediately preceding control block (an SVRB, Supervisor Call Request Block, an IRB, Interruption Request Block, or possibly the TCB itself), depending upon the particular context.
With the introduction of MVS/370 and successor systems, a whole new environment was introduced: the Service Request Block (SRB), which generally has a higher priority than any Task Control Block, and, indeed, which itself has two distinct priorities: a Global SRB (priority over all local address space SRBs and TCBs) and a Local SRB (priority over only the local address space TCBs); and MVS's dispatcher must manage all of these with absolute consistency across as many as two processors (MVS/370) and as many as sixteen processors (successor systems).