WGU C191: Ch 1: Intro to OS

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61 terms jacob_thomas6 Preview Computer Operating Systems - Alex...605 terms alexdoescode Preview WGU C 239 term njla Practice questions for this set Learn1 / 7Study using Learn It is the act of creating the illusion of having one or more objects with more desirable characteristics than the real object.OSs rely on this to create virtual CPUs, memory, I/O devices, and other system components that facilitate the work of programmers and users.The operating system (OS)It is the software that runs on the bare hardware of a computer and provides essential support for users to develop and use applications in the most efficient and safe manner.Choose an answer 1The operating system (OS)2Virtualization 3Privileged instruction4I/O devices Don't know?

CPUThis performs machine instructions on contents of registers and memory locations.Main memoryThis is physical memory in a linear sequence of addressable bytes or words that hold programs and data.Secondary storageThis is a multi-dimensional structures, which require complex sequences of low- level operations to store and access data organized in discrete blocks.I/O devicesThese devices are operated by reading and writing registers of the device controllers.AbstractionIt is the act of removing unimportant details or attributes of objects to construct more general and less complex objects.OSs make extensive use of this by creating hierarchies of objects where multiple operations at one level are combined into a single operation at a higher level, thus hiding the details of the implementation and making the operation easier to use.VirtualizationIt is the act of creating the illusion of having one or more objects with more desirable characteristics than the real object.OSs rely on this to create virtual CPUs, memory, I/O devices, and other system components that facilitate the work of programmers and users.MultiprogrammingIt is a technique that keeps several programs active in memory and switches execution among the different programs to maximize the use of the CPU and other resources.Whenever a program enters an I/O-bound phase where little CPU time is needed, other programs can resume and utilize the CPU in the meantime. Similarly, whenever a device completes an operation, the OS activates computations that can utilize the now available device.Time-sharing (multitasking)It is an extension of multiprogramming where the CPU is switched periodically among all active computations to guarantee acceptable response times to each user.This employs the concept of virtualization by creating the illusion of having a separate virtual CPU for each computation.MultiprogrammingIt generally improves CPU utilization and throughput.Multiprogramming vs Time sharingResource utilization is improved by multiprogramming, which overlaps CPU- bound and I/O-bound computations.Time-sharing only switches the CPU among different computations to create the illusion of simultaneous execution, which generally does not improve resource utilization beyond simple multiprogramming.Multiprogramming relationship with Time sharing Time-sharing requires multiprogramming since multiple computations must be active at the same time.

KernelIt is the minimal set of functions necessary to manage the system resources safely and efficiently.It typically provides the most essential services for memory and device management, for creating and managing units of computation, and for communication among the different concurrent activities within the system.Privileged instructionIt performs critical operations that access I/O devices and the CPU's status and control registers.Thus only the OS kernel is allowed to execute this.Kernel modeIt is the CPU state where both privileged and non-privileged instructions may be used.User modeIt is the CPU state where only non-privileged instructions may be used.Any attempt to execute a privileged instruction in user mode automatically transfers control to the kernel.Graphical user interface (GUI)It presets various icons on the screen, which the user can click on in different ways to invoke services associated with the icons, or to reveal pull-down menus for additional tasks.OS shellIt is a command interpreter that accepts and interprets textual commands issued by the user via a keyboard.Generic Shell Command: DIRDisplays a list of files and subdirectories in a directory (folder).

Generic Shell Command: COPYCopy one or more files to another location.

Generic Shell Command: WCCount the number of words, lines, and characters in a text file.

Generic Shell Command: DELDelete one or more files.

Generic Shell Command: What is * used for? The asterisk is a wildcard character, which can be substituted for zero or more characters in a string.The Main Advantage of a GUIintuitive visual representation of objects. A user is able to manipulate object and invoke operations using a mouse without much training and without any knowledge of the underlying commands.The Main Advantage of a Shellpreferred interface by programmers and expert users because text-based commands are more flexible than icons by providing a wide range of parameters and control flags to modify each command.

• Multiple commands can be combined using conditional, iterative, and logic

constructs to handle complex tasks efficiently.

• The user can create and save higher-level operations following the principles of

abstraction.

System callIt is a request from an application for an OS service.It is implemented as a library function, which sets up the necessary parameters for the requested operation and issues a corresponding supervisor call.Supervisor call (kernel call)It is a privileged instruction that automatically transfers execution control to a well-defined location within the OS kernel.Thus they provide the interface between the OS kernel and the higher-level software.

Supervisor callIt is similar to a function call with two special features:

• The call switches execution from user mode to kernel mode by setting the mode

bit in the CPU.

• In order to restrict the possibility of a call branching to unpredictable locations

within the kernel, the function to be executed is not directly identified by an address. Instead, it is indirectly specified through an index in a branch vector.Consequently, kernel-mode execution is constrained to specific and well-defined entry points within the kernel.InterruptIt is an event that diverts the current execution of a program to a predefined location in the kernel in order to respond to an event.It is triggered by a hardware signal sent to the CPU from an external device.

Uses of interruptsThe two most common uses of interrupts are:

• Signal to the OS the completion of an I/O operation. The interrupt is generated

by the I/O device,

• Implement time-sharing by periodically switching the CPU among multiple

concurrent computations. The interrupt is generated by a countdown timer.TrapIt is an interrupt triggered by the currently executing instruction.

Used for:

1. Exceptions: Dividing by zero, executing an invalid opcode, or causing an

arithmetic overflow

2. System call: Executing a supervisor call instruction

• Implementing certain debugging features

Called an internal interrupt Interrupt handlerIt is a kernel function, invoked whenever an interrupt occurs, that determines the cause of the interrupt and invokes the appropriate kernel function to provide the response.When the kernel function completes the requested service, the state of the interrupted computation is restored and control is returned to the instruction following the interrupt.The handling of an interrupt is thus completely transparent to the interrupted computation and provides an immediate response to asynchronous events.