Operating System Fundamentals

Operating System Fundamentals
97 Process – An instance of a program, consisting of one or more threads, that is currently be executed by a computer system. Process – the actual execution of program instructions, along with the memory and IO devices assigned to execute the given instructions. Process scheduling – using an algorithm (strategy) to determine which process should be executed next. Process state – The current status of a process that is being executed, or that is waiting to be executed by the CPU. Process Table – A tool used by the operating system to keep track of all processes and their current state. Processor preservation – the ability to hide multitasking concepts from the applications so that they do not know that other applications are running at the same time and sharing the CPU. Program Counter – A special register in the CPU that is used to hold the address of the next instruction code to be retrieved from memory. Programmed IO devices – Input/Output devices that require direct and complete control from the CPU. Protected mode – Also called protected virtual address mode. Allows the operating system, CPU and applications to take advantage of extended memory addresses and other system resources, such as virtual memory, paging and safe multitasking. pSOS – A specialized operating system for aircraft systems.
QNX – A specialized operating system for aircraft systems.
Quad-core – a computer system consisting of four processing units (CPUs). Quantum – the amount of time assigned by the Process Scheduler fora process to execute have the attention of the CPU) (see Time slice). Raise – when a thread gives a semaphore it is potentially waking up another thread that is waiting (see Give). Race condition – a sequence of code executed by two or more threads in which the end result depends on which thread finishes first. RAM – Random Access Memory. High speed, temporary data storage on specialized cards attached to the motherboard. Used to store data and instructions currently being used by the system. Random replacement – a virtual memory page replacement policy that works by randomly selecting pages from RAM to be swapped for pages from virtual memory. Typically, random replacement does notwork very effectively.

Operating System Fundamentals
98 Read only – a file attribute indicating that a file can be read, but cannot be modified by users.
Read/write arm – component inside of a hard disk drive that moves the read/write head across the surface of a platter.
Read/write head – component in a floppy disk drive or hard disk drive that reads and writes data on the surface of a magnetic storage disk. Ready – a process state where the process is marked as ready (waiting) for execution by the CPU. Real mode – Also called real address mode. A system state where the CPU and the computer are only capable of using a 16 bit addressing system and approximately 1 MB of memory built into the motherboard. Registers – Components inside the CPU used to store data. Relative path – the path to a file or folder on a storage device, relative to a predetermined parent folder. Replacement policy – a strategy used by the memory manager to manage swapping pages between RAM and virtual memory. Root – the base level of a hierarchical file structure on a storage device. Root directory – lists all of the files and subdirectories currently stored on the disk.
Round-robin scheduling – a process scheduling algorithm that executes each process from the Process Table in sequence, regardless of priority. Running – a process state where the process is currently being executed by the CPU. Scheduler – apiece of software code (it is generally a function) that is included as part of the operating system, and that is responsible for analyzing the Process Table and selecting the next process to be executed. Second Chance – aversion of the FIFO virtual memory page replacement policy that uses a reference bit to track whether a page in RAM has been used within a set amount of time. If the reference bit indicates that a page has been recently referenced, it will not be swapped into virtual memory. Sector – a physical division of a track (concentric circle) on the surface of a magnetic storage disk.
Self-yield – an inter process communication method where a process checks for the availability of a required variable, and voluntarily goes into a blocked state if the variable is not available allowing another processor thread to gain access to the CPU. Semaphore – a special type of variable used in inter process communication to support the wait take) and raise (give) operations (see Signal).

Operating System Fundamentals
99 Shared files – files that have been marked as shared so that they can be accessed by users other than the original creator/owner of the file. Shared memory – when multiple threads have access to the same piece of memory, and each has the ability to read and write to that memory location at the same time. Shared requests folder – part of a device driver used to store requests that have been received from the operating system with instructions to be carried out by a device. Shortest task remaining – a process scheduling algorithm that attempts to determine which process in the Process Table has the shortest time remaining to be completed, and then selects that process to be executed next. Signal – a special type of variable used in inter process communication to support the wait take) and raise (give) operations (see Semaphore). Sleep – a command that causes a processor thread) to go into a blocked state fora specified amount of time. Southern Bridge – A component that regulates the flow of electronic information from the
Input/Output busses to the main system bus. Special purpose operating system – an operating system designed for specialized computerized devices. Starvation – when a process never gets a chance to run because a higher priority process is using too much processor time. State changing – changing the state of a process to mark it as either Running, Ready, Blocked,

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