Kernel – a portion of the operating system that includes the most heavily used portions of software. Generally, the kernel is maintained permanently in main memory. The kernel runs in a privileged mode and responds to calls from processes and interrupts from devices.
Lightweight Process – a thread
Macrokernel – a large operating system core that provides a wide range of services
Main Memory – memory that is internal to the computer system, is program addressable, and can be loaded into registers for subsequent execution of processing
Message – a block of information that may be exchanged between processes as a means of communication
Microkernel – a small privileged operating system core that provides process scheduling, memory management, and communication services and relies on other processes to perform some of the functions traditionally associated with the operating system kernel
Mode Switch – a hardware operation that occurs that causes the processor to execute in a different mode (kernel or process). When the mode switches form process to kernel, the program counter, processor status word, and other registers are saved. When the mode switches from kernel to process, this information is restored.
Monolithic Kernel – a large kernel containing virtually the complete operating system, including scheduling, file system, device drivers, and memory management. All the functional components of the kernel have access to all of its internal data structures and routines. Typically, a monolithic kernel is implemented as a single process, with all elements sharing the same address space.
Multiprocessing – a mode of operation that provides for parallel processing by two or more processors of a multiprocessor
Multiprocessor – a computer that has two or more processors that have common access to a main storage
Multiprogramming – a mode of operation that provides for the interleaved execution of two or more computer programs by a single processor. The same as multitasking, using different terminology.
Multitasking – a mode of operation that provides for the concurrent performance or interleaved execution of two or more computer tasks. The same as multiprogramming, using different terminology.
Mutual Exclusion – a condition in which there is a set of processes, only one of which is able to access a given resource or perform a given function at any time. See critical section.
Network Operating System – the software, supplemental to the operating system, that provides support for the use of common server systems in a network of computers
Nonprivilaged State – an execution context that does not allow sensitive hardware instructions to be executed, such as the ‘interrupt disable’ and I/O instructions
Operating System – software that controls the execution of programs and that provides services such as resource allocation, scheduling, input/output control, and data management
Preemption – reclaiming a resource from a process before the process has finished using it
Privileged Instruction – an instruction that can be executed only in a specific mode, usually by a supervisory program
Process – a program in execution. A process is controlled and scheduled by the operating system. Same as task.
Process Control Block – the manifestation of a process in an operating system. It is a date structure containing information about the characteristics and state of the process.
Process Descriptor – same as process control block
Process Image – all of the ingredients of a process, including program, data, stack, and process control block
Process State – all of the information that the operating system needs to manage a process and that the processor needs to properly execute the process. The process state includes the contents of the various processor registers, such as the program counter and data registers; it also includes information of use to the operating system, such as the priority of the process and whether the process is waiting for the completion of a particular I/O event. Same as execution context.
Process Switch – an operation that switches the processor from one process to another, by saving all the process control block, registers, and other information for the first and replacing them with the process information for the second
Round Robin – a scheduling algorithm in which processes are activated in a fixed cyclic order. Those which cannot proceed because they are waiting for some event (e.g., termination of a child process or an input/output operation) simply return control to the scheduler.
Secondary Memory – memory located outside the computer system itself, including disk and tape
Shell – the portion of the operating system that interprets interactive user commands and job control language commands. It functions as an interface between the user and the operating system.
Stack – a list that is constructed and maintained so that the next data item to be retrieved is the most recently stored item in the list. This method is characterized as last-in-first-out
Starvation – a condition in which a process in indefinitely delayed because other processes are always given preference
Symmetric Multiprocessing (SMP) – a form of multiprocessing that allows the operating system to execute on any available processor or on several available processors simultaneously
Synchronization – situation in which two or more processes coordinate their activities based on a condition
Task – same as process
Thread – an execution context that is independently scheduled but shares a single address space with other threads
Time Sharing – the concurrent use of a device by a number of users
Time Slicing – a mode of operation in which two or more processes are assigned quanta of time on the same processor
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