Recall, from this chapter, that the factor gamma | Ch 35 - 5P

1 Define an operating system An operating system is a program/software that acts as an interface between the user and the computer hardware and controls the execution of all kinds of programs. 2 Computer types Micro, mini, mainframe, super 3 Describe the evolution and trends of the operating system 1940: First generation Computer based on vacuum tube technology 1950: Second generation Focused on cost effectiveness 1960: Third generation Multiprogramming, program scheduling 1970 Virtual memory developed to solve physical limitation 1980 Multiprocessing 1990 Demand for internet capability, and multimedia applications 2000 virtualization 4 Distinguish an operating system from a computer system Computer system is software (program). Hardware (physical machine and electric components. Operating System is part of computer system (software) and manages all hardware and software 5 Computer object oriented design  Load only the critical elements into the main memory and call other objects as needed.  Kernel (operating system nucleus) o Resides in memory at all times, performs essential tasks, and protected by hardware  Kernel reorganization o Memory resident: process scheduling and memory allocation o Modules: all other functions  Advantages o Modification and customization without disrupting integrity of the remainder of the system o Software development more productive 6 Explain the operations of an operating system Monitor its resources continuously. Enforce the policies that determine who gets what, when and how much. Allocate the resource when appropriate De­allocate the resource when appropriate 7 List the different categories of operating systems Five types/categories: Batch, Interactive, Real­time, Hybrid, Embedded Two distinguishing features = Response time and How data enters into the system 8 Identify the key operating system managers  Memory Manager: the section of the operating system responsible for controlling the use of memory. It checks the validity of each request for memory space and, if it’s a legal request, allocates the amount needed to execute the job. Ram  Processor Manager: a composite of two sub­managers, the Job Scheduler and the Process Scheduler, which decides how to allocate the CPU. CPU  Device Manager: the section of the operating system responsible for controlling the use of devices. It monitors every device, channel, and control unit and chooses the most efficient way to allocate all of the system’s devices. Keyboard, printer, disk drive  File Manager: the section of the operating system responsible for controlling the use of files. Program files, data files, compilers.  Network Manager: the section of the operating system responsible for controlling access to and the use of networked resources. Network Comms, protocols 9 Describe the early memory management allocation schemes  Single­user contiguous,  Fixed partitions,  Dynamic partitions Common requirements of old memory management techniques (Disadvantages of the old schemes)  Entire program loaded into memory  Contiguous storage  Stays in memory until job completed  Each places severe restrictions on job size  Sufficient for first three generations of computers  Multiprogramming not supported in Single­user contiguous 10 Describe the new memory management allocation schemes  Paged memory allocation o Divides each incoming job into pages of equal size  Demand paging scheme o Pages brought into memory only as needed  Segmented memory allocation scheme o Each job divided into several segments (logical pieces), where the segments are different sizes  Segmented/demand paged memory o Combination of segmentation and demand paging  Virtual memory o Combination of RAM and disk space that running processes can use.  First­fit memory allocation ­ first partition fitting the requirements o Advantage: faster in making allocation o Disadvantage: leads to memory waste  Best­fit memory allocation ­ smallest partition fitting the requirements o Advantage: makes the best use of memory space o Disadvantage: slower in making allocation 11 Explain the process management concept and concurrency of operating systems Processor Manager ­ Composite of two sub­managers  Job Scheduler: higher­level scheduler o Job scheduling responsibilities o Job initiation based on certain criteria  Process Scheduler: lower­level scheduler o Process scheduling responsibilities o Determines execution steps o Process scheduling based on certain criteria  HOLD (handled by Job Scheduler)  READY (handled by Process Scheduler)  WAITING (handled by Process Scheduler)  RUNNING (handled by Process Scheduler)  FINISHED (handled by Job Scheduler) Six algorithm types  First­come, first­served (FCFS) – non­preemptive  Shortest job next (SJN) – non­preemptive  Priority scheduling – non­preemptive  Shortest remaining time (SRT) – preemptive  Round robin (RR)– preemptive  Multiple­level queues – more of a package, 1 queue per policy Concurrency is a property of systems in which several computations are executing simultaneously, and potentially interacting with each other  Multiple processes within OS  Multiple threads within a process There is no need for ‘rules’ if there is no shared resources (e.g. data) or resource/data is constant (read­only), otherwise we need synchronization… Lack of process synchronization consequences • Deadlock: “deadly embrace” • System comes to standstill • Resolved via external intervention • Starvation • Infinite postponement of job 12 Identify the four basic functions of device management  Monitoring of status of each device  Enforcing policies to determine which process will get a device and for how long.  Allocating the device  De­allocating the device  Dedicated Devices (e.g. printer)  Shared Devices (e.g. hard disk)  Virtual Devices  A virtual device is a combination of dedicated and shared devices. It is actually a dedicated device which is transformed to a shared device. (E.g. printer converted to shareable device through a spooling program which reroutes all print requests to a disk.)  Sequential access disk  DASD  Flash memory optical disk, magnetic disk, fixed and movable head Ready – determined by process scheduling algorithms Waiting – signal to continue processing Running – l/0 request page fault Divide each job into equal size Pages brought into memory only as needed Each job divided into different size, segment are different size Combination Combination of RAM and disk space that running process can use It checks the validity of each request for memory space and, if it’s a legal request, allocates the amount needed to execute the job. which decides how to allocate the CPU. Controlling access to and the use of networked resources. 13 Explain the fundamentals of file management and the structure of the file management system  In a computer system, the File Manager keeps track of its files with directories that contain the filename, its physical location in secondary storage, and important information about each file.  File storage tracking  Policy implementation  File allocation if user access cleared  File de­allocation  Field – group of related byte  Record – group of related field  File – group of related record (information used by specific program)  File Organization refers to the arrangement of records within the file  Sequential record organization ­ easiest to implement because records are stored and retrieved serially, one after the other.  Direct record organization ­ uses direct access files, which, of course, can be implemented only on direct access storage devices  Indexed sequential record organization ­ combines the best of sequential and direct access.