Table lists typical elements found in a process control block for an unthreaded OS. Of these, which should belong to a thread control block and which should belong to a process control block for a multithreaded system?

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Process Identification Identifiers Numeric identifiers that may be stored with the process control block include . Identifier of this process. Identifier of the process that created this process (parent process) . User identifier Processor State Information User-Visible Registers A user-visible register is one that may be referenced by means of the machine language that the processor executes while in user mode. Typically, there are from 8 to 32 of these registers, although some RISC implementations have over 100 Control and Status Registers These are a variety of processor registers that are employed to control the operation of the processor. These nclude . Program counter: Contains the address of the next instruction to be fetched. e Condition codes: Result of the most recent arithmetic or logical operation (e.g., sign, zero, carry, equal, overflow) e Status information: Includes interrupt enabled/disabled flags, execution mode Stack Pointers Each process has one or more last-in-first-out (LIFO) system stacks associated with it. A stack is used to store parameters and calling addresses for procedure and system calls. The stack pointer points to the top of the stack Process Control Information Scheduling and State Information This is information that is needed by the operating system to perform its scheduling function. Typical items of information: Process state: Defines the readiness of the process to be scheduled for execution (e.g., running, ready waiting, halted) . Priority: One or more fields may be used to describe the scheduling priority of the process. In some systems, several values are required (e.g., default, current, highest-allowable) e Scheduling-related information: This will depend on the scheduling algorithm used. Examples are the amount of time that the process has been waiting and the amount of time that the process executed the last time it was running . Event: Identity of event the process is awaiting before it can be resumed Data Structuring A process may be linked to other process in a queue, ring, or some other structure. For example, all processes in a waiting state for a particular priority level may be linked in a queue. A process may exhibit a parent-child (creator-created) relationship with another process. The process control block may contain pointers to other processes to support these structures Interprocess Communication Various flags, signals, and messages may be associated with communication between two independent processes. Some or all of this information may be maintained in the process control block. Process Privileges Processes are granted privileges in terms of the memory that may be accessed and the types of instructions that may be executed. In addition, privileges may apply to the use of system utilities and services Memory Management This section may include pointers to segment and/or page tables that describe the virtual memory assigned to this process Resource Ownership and Utilization Resources controlled by the process may be indicated, such as opened files. A history of utilization of the processor or other resources may also be included; this information may be needed by the scheduler