Week 11 Notes - Chapter 3 Operating Systems
Week 11 Notes - Chapter 3 Operating Systems CSC 2310
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This 5 page Class Notes was uploaded by Taylor Kahl on Saturday April 2, 2016. The Class Notes belongs to CSC 2310 at Georgia State University taught by Kebina Manandhar in Winter 2016. Since its upload, it has received 12 views. For similar materials see Princliples of Computer Programming in ComputerScienence at Georgia State University.
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Date Created: 04/02/16
Chapter 3: Operating Systems Operating system – a software package that oversees the computer’s operation o coordinates a computer’s internal activities o manages communication w/ outside world o allows you to store & retrieve files o provides the environment needed to execute programs o Examples: Windows (Microsoft) UNIX – the core of 2 other OS’s: Mac OS (Apple) Solaris (owned by Oracle) Linux (available through IBM) History of operating systems: Originally, people had to share computers, set up their program or job, wait for it to execute and them remove all their equipment so the next person could use it o Operating systems smooth the transition between performing different jobs Batch processing – if you wanted to run a program, had to submit it to the computer operator o the operator would load everyone’s programs in a single “batch” into the machine’s mass storage o the operating system would read and execute each program one at a time job queue – the jobs in mass storage waiting to be executed st st 1 job inputted is the 1 to be executed o drawback: can’t interact w/ the program once it’s been submitted to the operator Interactive processing – allows programs being executed to communicate w/ the user o this requires real-time processing – the computer has to execute tasks quickly enough for the user to interact w/ it Example of real-time processing: seeing characters appear when you type using a word processor o drawback: originally computers had to serve multiple people at once could only perform in “real-time” w/ one person at a time Time-sharing – multiple users could interact w/ the computer simultaneously o time-sharing implemented through multiprogramming – time is divided into intervals; execution of each job is restricted to one interval of time at the end of a time interval, the current program is paused & another one executes during the next interval gives the illusion that multiple jobs are being executed simultaneously for multiple users o Multitasking refers to 1 user running multiple jobs simultaneously Multiprocessor machines – the operating system can assign different jobs to different processors (true multitasking) & use time-sharing within individual processors o load balancing – dynamically assigning tasks to processors so that each one is used efficiently o scaling – breaking tasks into subtasks based on the # of available processors Types of software: Application software – performs specific tasks for users o Examples: spreadsheets, database systems, games System software – provides the infrastructure that application software needs to be able to run o consists of utility software & OS (operating system) o Utility software – programs for the computer’s installations extends the capabilities of the OS Examples: software to compress/decompress data, to play multimedia, to handle network communication Components of an operating system: User interface – communicates w/ the user o Shells – text communication through the monitor & keyboard (older type of interface) o Graphical user interface (GUI) – objects are represented by picture icons lets users click/drag icons w/ a mouse, stylus or finger window manager – allocates blocks of space on the screen; keeps track of which app is associated w/ which window; allows apps to be displayed in the appropriate window Kernel – internal part of the OS; performs basic required functions o File manager – coordinates use of the computer’s mass storage a record of each file, where it’s stored, & how much mass storage is still available Directory – a bundle of files that lets the user organize related files into folders or subdirectories Directory path – a chain of directories within directories o Device drivers – communicate w/ controllers or periphery devices Example: a device driver for a printer can read & decode the printer’s status and manage printing o Memory manager – coordinates computer’s use of main memory finds & assigns memory space for programs; restrict program to its assigned space virtual memory – if a program requires more main memory than is available, the memory manager will use paging to shuffle data back and forth from a disc to main memory, so that only the data needed at that moment is in main memory o Scheduler – determines what activities are to be considered for execution o Dispatcher – controls the allocation of time to those activities Getting the operating system started: Bootstrapping (booting) – every time computer is turned on o boot loader program is permanently stored in the computers ROM (read-only memory) boot loader instructs the CPU to transfer the OS into main memory then the boot loader instructs the CPU to execute a jump instruction to the area of main memory where the OS is stored o At this point, the OS takes over control Coordinating the computer’s activities Process – the activity of executing a program Process state – current status of activity. Includes: o value of program counter – current position in program being executed o values of CPU registers o values of associated memory cells Coordinating the execution of processes is handled by the scheduler & dispatcher in the kernel o Scheduler maintains a process table – information in main memory keeps track of processes present in the computer system adds new processes removes completed processes o Dispatcher uses multiprogramming to execute scheduled processes each process allocated a time slice each time signal has an interrupt signal when time runs out the CPU switches from the current process to another at the end of its time slice the CPU saves its current position in the process then the dispatcher chooses the process that has the highest priority to be executed next Handling competition among processes Semaphore – a “flag” or signal that a process is available o Example: a process requests access to the printer through the OS. The OS must check the flag on the printer: is it in use or available? The OS can also change the value of the flag once the printer is in use o critical region – a sequence of instructions that should only be executed by 1 process at a time o mutual exclusion – the requirement that only 1 process at a time can execute a critical region Deadlock – when multiple processes are blocked because they are waiting for a resource that is allocated to another process o Example: 1 process has access to the printer & is waiting for access to the CD player; another process has access to the CD player & is waiting on the printer o Deadlock will only occur if all of these conditions are met: Competition for non-shareable resources Resources are requested on a partial basis – process will receive some resources and return later to ask for more once a resource has been allocated, it can’t be forcibly retrieved Security: Attacks from the outside: o insecure passwords o sniffing software – records the activities running on a computer and reports them to an intruder Protection: auditing software – record & analyze the computer’s activities o can identify unauthorized attempts to access computer or unusual activities Attacks from within: o unruly processes (once an intruder has gained access) Protection: o privileged modes – CPUs operate in privileged or non-privileged mode o privileged instructions are only allowed when the CPU is in privileged mode
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