Kapitel 3 Flashcards
Explain what the operating system is, and where it resides in regards to software classification
Operating system – is the software that controls the overall operation a computer. It provides the means by which a user can store and retrieve files, provides the interface by which a user can request the execution of programs and provides the environment necessary to execute the programs requested.
Software classification – Software (Application and System), System (Utility and Operating system), Operating system (User interface and Kernel)
What does the scheduler do?
Scheduler – Determines which activities are to be considered for execution. The scheduler maintains a record of the processes present in the computers system, introduces new processes to this pool and removes completed processes from the pool. Thus when a user requests the execution of an application, it is the scheduler that adds the execution of that application to the pool of current processes. The scheduler maintains a block of information in main memory called the process table. Each time the execution of a program is requested the scheduler creates a new entry for that process in the process table. This entry contains such information as the memory area assigned to the process, the priority of the process, and whether the process is ready or waiting.
What is the memory manager?
Memory manager – The memory manager is charged with the task of coordinating the machine’s use of main memory. Such duties are minimal in an environment in which a computer is asked to perform only one task at a time. In these cases, the program for performing the current task is placed at a predetermined location in main memory, executed, and then replaced by the program for performing the next task. However, in multiuser or multitasking environments in which the computer is asked to address many needs at the same time, the duties of the memory manager are extensive.
Explain the concepts of paging and virtual memory
Paging – a technique the memory manager uses to create the illusion of additional memory by rotating programs and data back and forth between main memory and mass storage.
Virtual memory – The large “fictional” memory space created by paging.
What is the difference between time-sharing, multiprogramming and multi-tasking?
Time-sharing – when a computer provides service to several users at a time
Multiprogramming – time is divided into intervals and then the execution of each job is restricted to only one interval at a time. At the end of each interval, the current job is temporarily set aside and another is allowed to execute during the next interval. By rapidly shuffling the jobs back and forth in this manner, the illusion of several jobs executing simultaneously is created.
Multitasking – when one user is executing numerous tasks simultaneously.
Explain batch-, interactive-, and real time processing
Batch processing – the execution of jobs by collecting them in a single batch, then executing them without further interaction with the user.
Interactive processing – When an operating system allows a program being executed to carry on a dialogue with the user.
Real time processing – When a computer is forced to execute tasks under a deadline, when actions are said to occur in real time.
What is system software?
System software – Performs those tasks that are common to computer systems in general. In a sense, the system software provides the infrastructure that the application software requires, in much the same manner as a nation’s infrastructure (government roads, utilities, financial institutions etc.) provides the foundation on which its citizens rely for their individual lifestyles.
What is application software?
Application software – Consists of the programs for performing tasks particular to the machines utilization. A machine used to maintain the inventory for a manufacturing company will contain different application software from that found on a machine used by an electrical engineer. Examples of application software include spreadsheets, database systems, desktop publishing systems, accounting systems, program development software, and games.
Explain the process of boot strapping
Boot strapping (booting) – We need a program (preferably the operating system) to be present in main memory when the computer is first turned on. A small portion of a computer’s main memory where the CPU expects to find its initial program is constructed from special nonvolatile memory cells. Such memory is known as read-only memory (ROM). A program called the bootloader is permanently stored in the machines ROM. This is the program that is initially executed when the machine is turned on. This program contains instructions to direct the CPU to transfer the operating system from a predetermined location into the volatile area of main memory.
Explain what the kernel is and what it consists of
Kernel – in contrast to an operating systems user interface. The internal part of an operating system. Contains those software components that perform the very basic functions required by the computer installation. One such unit is the file manager, whose job is to coordinate the use of the machine’s mass storage facilities. More precisely, the file manager maintains records of all the files stored in mass storage, including where each file is located, which users are allowed to access the various files, and which portions of mass storage are available for new files or extensions to existing files.Another component of the kernel consists of a collection of device drivers. Another component of the operating system’s kernel is the memory manager. Two additional components of the kernel is the scheduler and dispatcher.
What is Utility software?
Utility software – The majority of an installations utility software consists of programs for performing activities that are fundamental to computer installations but not included in the operating system. In a sense, utility software consists of software units that extend (or perhaps customize) the capabilities of the operating system. For example, the ability to format a magnetic disk.
What does the dispatcher do?
Dispatcher – Controls the allocation of time to the activites the scheduler decides to execute. The dispatcher is the component of the kernel that oversees the execution of the scheduled processes. In a time-sharing/multitasking system this task is accomplished by multiprogramming. That is dividing time into short segments, each called a time slice (typically measured in milliseconds or microseconds), and then switching the CPU’s attention among the processes as each is allowed to execute for one time slice. The procedure of changing from one process to another is called a process switch (or a context switch). Paramount to the success of a multiprogramming system is the ability to stop, and later restart, a process.
What is a process and what is the difference between a process and a program?
Process – The activity of executing a program under the control of the operating system. Associated with a process is the current status of the activity, called the process state. This state includes the current position in the program being executed (the value of the program counter) as well as the values on the other CPU registers and the associated memory cells. The process state is a snapshot of the machine at a particular time.
What is the difference between a program and a process? – The former is a static set of directions, whereas the latter is a dynamic activity whose properties change as time progresses.
Explain the concepts of “flag”, “test-and-set” and semaphores
Flag – a bit in memory whose states are often referred to as set and clear. A clear flag (0) indicates that the printer is available and a set flag (1) indicates that the printer is currently allocated.
Test-and-set – An instruction available in many machine languages. This instruction directs the CPU to retrieve the value of a flag, note the value received, and then set the flag – all within a single machine instruction. The advantage here is that because the CPU always completes an instruction before recognizing an interrupt, the task of testing and setting the flag cannot be split when it is implemented as a single instruction.
Semaphore – A properly implemented flag, in reference to the railroad signals used to control access to sections of track. Semaphores are used in software systems in much the same was as they are in railway systems. Correpsonding to the section of track that can contain only one tran at a time is a sequence of instructions that should be executed by only one process at a time. Such a sequence of instructions is called a critical region.
What is sniffing software?
Sniffing-software – software that, when left running on a computer records activities and later reports them to a would-be intruder. An old, wellknown example is a program that simulates the operating system’s login procedure. Such a program can be used to trick authorized users into thinking they are communicating with the operating system, whereas they are actually supplying their names and passwords to an impostor.
