Account Information: It is a piece of information associated with processes. This information includes the amount of CPU and real time used, time limits, account numbers, job or processes numbers, and so on.
Blocked-State: Process state in which the process cannot proceed until it receives a particular resource or message.
Bonded capacity: When the queue has a finite length n, thus at most n messages can reside in it.
Buffering: A link capacity that determines the number of messages that can reside in it temporarily. Property also viewed as a queue of messages attached to the link.<,p> Computation Speedup: Is the breaking of a task into subtasks, each of which will be executing in parallel with the others. The breaking of the tasks allows a particular task to run faster, but such speed up can only be achieved if the computer has multiple processing elements, such as CPUs or I/O channels.
Consumer: Consumes information that is produced by the producer.
Counter Measure: Is a study of how users may attempt to manipulate the system in a selfish way and what can be done to prevent it.
Context Switch : Task which saves the state of an old process and loads the saved state for the new process, while switching the CPU to another process.
CPU Time: Amount of time allocated to each process by the CPU for their execution.
CPU Registers: Piece of information associated with a specific process. Registers can vary in type and also in number, everything depends on the computer architecture. They include stack pointers, accumulators, index registers, and other general purpose registers. Along with the program counter, this state information must be saved when an interrupt occurs, to allow the process to be continued correctly afterward.
CPU Scheduling Information: Additional piece of information associated with specific processes. This information includes a process priority, pointers to scheduling queues, and any other scheduling parameters.
Deadlock: Situation in which processes are in a waiting state, with the chances of never changing such state, because the resources requested are held by other waiting processes.
Direct Communication: Discipline in which each process that wants to communicate must explicitly name the recipient or sender of the communication. Dynamically: Step in used in the creation of a process in which each process may contain the declaration of a flexible set of subprocesses.
File: A logical storage unit.
Fork: A system call used in UNIX operating systems to create new processes.
I/O Status Information: Information that includes the list of I/O devices (such as tape drives) allocated to this process, a list of open files, and so on.
I/O Devices: Devices utilized for Input/Output operations or processes.
Indirect Communication: Discipline in which the messages are sent to and received from mailboxes (also referred to as ports), objects where processes place and remove their messages. Each box has a unique identification. In this scheme a process can communicate with some other process via a number of different mailboxes.
Information sharing: Scheme in which different users can share the same piece of information that they are interested on (for example a shared file). The environments should allow concurrent access to all types of resources.
Kernel: A common definition for operating system programs that are running all times on the computer, with all else being application programs.
Lightweight process (LWP): Also called Threads, is a basic unit of CPU utilization, and consists of a program counter, a register set, and a stack space.
Memory: Computer hardware that provides one of the basic computing services, storage.
Memory-Management Information: Information associated with specific processes, which may include the value of the base and limit registers, the page tables, or the segment tables depending on the memory system used by the operating system.
Message System: Function that allow processes to communicate with each other without the need to resort to shared variables.
Modularity: Approach that simplifies debugging and system verification. Recognized as the main advantage of the layered approach, since the layers are selected such that each uses functions (operations) and services of only lower-level layers.
Modules: A self contained assembly of electronic components and circuitry, such as a stage in a computer.
New-State: State in which the process is being created.
Process: It is an instance of an active program. Is a copy of the program that has been assigned computer resources.
Process Control Block (PCB): Represents each process in the operating system. Also known as the Task Control Block.
Process Creation: Creation of several new processes by a process, via a create-process system call, during the course of execution.
Process State: The states associated with specific processes. States that it may include are new, ready, running, waiting, blocked, and so on.
Process Termination: Occurs when a process finishes executing its last statement and asks the operating system to delete it by using the exit system call.
Producer: Type of process that produces information that is consumed by a consumer process.
Program: Is basically a set of instructions (an executable file) for carrying out some computing activity.
Program Counter: Information associated with processes. The counter will indicate the address of the next instruction to be executed by this process.
Ready-State: State in which the process is waiting to be assigned to a processor.
Resources: Available supplies that can be drawn upon when needed.
Running-State: State where the instructions are being executed.
Schedule: Program of forthcoming events or processes, with a timetable of departures and arrivals.
Starvation: The state in which a process may need several popular resources and may have to wait indefinitely, because at least one of the resources that it needs is always allocated to some other process.
State: Condition of being with regard to a set of circumstances; position.
Statically: Process declaration of a fixed set of subprocesses, all of which may be activated when a process begins its execution.
Subprocess: Division of a process.
Synchronization: Occurrence of events at the same time, simultaneously.
Task: Execution of a job in a batch system, or user programs in a time-shared system.
Task Control Block: Represents each process in the operating system. Also known as the Process Control Block.
Terminated-State: State where the process has finished its execution.
Thread: Sometimes called a lightweight process (LWP) is a basic unit of CPU utilization, and consists of a program counter, a register set, and a stack space.
Unbounded capacity: When the queue has potentially infinite length; thus any number of messages can wait in it. The sender is never delayed.
Utilization: Having something in use for a certain purpose.
User-level threads: Implementation used in user-level libraries, where the thread switching does not need to call the operating system, avoiding to cause an interruption to the kernel.
Virtualize: Existence or resulting in essence or effect though not in actual fact, form, or name.
Virtual Memory: Technique that allows the execution of a job that may not be completely in memory.
Waiting-State: State where the process is waiting for some event to occur (such as an I/O completion or reception of a signal).
Wait: A system call used by UNIX operating system, which can help the parent to move itself off the ready queue until its child is terminating its running during execution.