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1 SYSC3001 Operating Systems and Data Bases n From calendar: u Management of CPU (scheduling) processes, memory, disk, and files. u Implications of concurrency.

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Presentation on theme: "1 SYSC3001 Operating Systems and Data Bases n From calendar: u Management of CPU (scheduling) processes, memory, disk, and files. u Implications of concurrency."— Presentation transcript:

1 1 SYSC3001 Operating Systems and Data Bases n From calendar: u Management of CPU (scheduling) processes, memory, disk, and files. u Implications of concurrency. u Concurrent programming, including interprocess communications in distributed systems. u Data base models and query languages.

2 2 Computer Systems Overview n Basically Chapter 1 in textbook n Need some basic understanding of computer organization and hardware: u processor u memory u I/O devices n “Left as an exercise”

3 Chapter 2: Operating Systems Overview n What is an Operating System? n Services provided by an OS n Evolution of the OS n Desired Hardware Features to support the OS n Multiprogramming n Time Sharing Systems n Difficulties of the OS Design n Achievements of the OS n System Structure of the OS n Modern OS 3

4 4 Operating System n Is a program that controls the execution of application programs u Tells the CPU when to execute other programs u Uses the hardware efficiently n Is an interface between the user and hardware u Masks the details of the hardware to application programs u Hence OS must deal with hardware details u Make the system convenient to use

5 5 Layers and Views The OS typically is further divided into multiple layers.

6 Operating Systems Definitions n Resource manager: manages and allocates resources (CPU, memory, I/O, software processes) n Control program: control the execution of user programs n Kernel: the one program running at all times (all else being application programs) 6

7 7 Services Provided by the OS n Facilities for Program creation u editors, compilers, linkers, and debuggers n Program execution u loading in memory, I/O and file initialization n Access to I/O and files u deals with the specifics of I/O and file formats n System access u Protection in access to resources and data u Resolves conflicts for resource contention

8 8 Services Provided by the OS n Error Detection u internal and external hardware errors F memory error F device failure u software errors F arithmetic overflow F access forbidden memory locations u Inability of OS to grant request of application n Error Response u simply report error to the application u Retry the operation u Abort the application

9 9 Services Provided by the OS n Accounting u collect statistics on resource usage u monitor performance (e.g., response time) u used for system parameter tuning to improve performance u useful for anticipating future enhancements u used for billing users (on multiuser systems)

10 Quiz 2-1 1.What is an OS? A. Application program B. Interface between user programs C. Resource manager D. Kernel 2.Name two OS services. 10

11 11 Evolution of the Operating System n Must adapt to hardware upgrades and new types of hardware. Examples: u Character vs. graphic terminals u Introduction of paging hardware n Must offer new services, e.g., Internet support n The need to change the OS software on a regular basis u modular construction with clean interfaces u object oriented methodology

12 12 Simple Batch Systems n First generation OS (mid-50s) n Main objective is to maximize utilization n The user submits a job (written on card or tape) to a computer operator n The computer operator places a batch of several jobs on a input device n The OS, the monitor, manages the execution of each program in the batch u Monitor mostly is in main memory and available for execution, Resident Monitor u Monitor utilities are loaded when needed

13 13 The Monitor n Monitor reads in jobs one at a time from the input device n Monitor places a job in the user program area n A monitor instruction branches to the start of the user program n Execution of user program continues until: u end-of-program occurs u error occurs n Causes the CPU to fetch its next instruction from Monitor

14 14 Job Control Language (JCL) n Is the special type language to provide instructions to the monitor u what compiler to use u what data to use n Example of job format: u $JOB shows a new job  $FTN loads the compiler and transfers control to it  $LOAD loads the object code (in place of compiler)  $RUN transfers control to user program $JOB $FTN... FORTRAN program... $LOAD $RUN... Data... $END

15 15 Job Control Language (JCL) During user program execution: n Each read (or input) instruction (in user program) causes one line of input data to be read n Causes an input routine to be invoked u checks for not reading a JCL line u skips to the next JCL line at completion of user program

16 16 Simple Batch OS n Alternates execution between a user program and the monitor program n Relies on available hardware to effectively alternate execution from various parts of memory

17 17 Desirable Hardware Features n Memory protection u do not allow the memory area containing the monitor to be altered by user programs n Timer u prevents a job from monopolizing the system u an interrupt occurs when time expires

18 18 Desirable Hardware Features n Privileged instructions u can be executed only by the monitor u an interrupt occurs if a program tries these instructions n Interrupts u provides flexibility for relinquishing control to and regaining control from user programs

19 Transfer of Control via Interrupts 19

20 20 Main Problem with Batch Systems - System Utilization Example

21 21 Multiprogrammed Batch Systems n I/O operations are exceedingly slow (compared to instruction execution) n A program containing even a very small number of I/O operations will spend most of its time waiting for them n Hence: poor CPU usage when only one program is present in memory

22 22 Multiprogrammed Batch Systems n If memory can hold several programs, then CPU can switch to another one whenever a program is awaiting for an I/O to complete n This is multitasking (multiprogramming)

23 23 Requirements for Multiprogramming n Hardware support: u I/O interrupts and (possibly) DMA F in order to execute instructions while I/O device is busy u Memory management F several ready-to-run jobs must be kept in memory u Memory protection (data and programs) n Software support from the OS: u Scheduling (which program is to be run next) u To manage resource contention and concurrency

24 24 Example: three jobs are submitted n Almost no contention for resources n All 3 can run in minimum time in a multitasking environment (assuming JOB2/3 have enough CPU time to keep their I/O operations active) n Total memory size is 256M bytes. JOB1 JOB2JOB3 Type of jobHeavy computeHeavy I/OHeavy I/O Duration 5 min.15 min.10 min. Memory req.50M100 M80 M Need disk?NoNoYes Need terminalNoYesNo Need printer?NoNoYes

25 25 Advantages of Multiprogramming UniprogrammingMultiprogramming Processor use17%33% Memory use33%67% Disk use33%67% Printer use33%67% Elapsed time30 min.15 min. Throughput rate6 jobs/hr12 jobs/hr Mean response time18 min.10 min.

26 26 Time Sharing Systems (TSS) n Batch multiprogramming does not support interaction with users n TSS extends multiprogramming to handle multiple interactive jobs n Processor’s time is shared among multiple users n Multiple users simultaneously access the system through terminals

27 27 Time Sharing Systems (TSS) n Because of slow human reaction time, a typical user needs 2 sec of processing time per minute n Then (about) 30 users should be able to share the same system without noticeable delay in the computer reaction time n The file system must be protected (multiple users…)

28 28 Difficulties with OS Design n Improper synchronization u ensure a program waiting for an I/O device receives the signal n Failed mutual exclusion u must permit only one program at a time to perform a transaction on a portion of data n Deadlock u It might happen that 2 or more programs wait endlessly after each other to perform an operation.

29 29 An example of deadlock n Program A wants to copy from disk1 to disk2 and takes control of disk1 n Program B wants to copy from disk2 to disk1 and takes control of disk2 n Program A must wait that program B releases disk2 and program B must wait that program A releases disk1 n Program A and B may wait forever

30 Quiz 2-2 n What is multiprogramming? n Multiprogramming vs. uniprogramming u Main advantage? u Challenges? n True of False u Time sharing systems (TSS) are multiprogramming u Multiprogramming systems are TSS n Batch multiprogramming vs. TSS u Key objective u Source of directives to OS 30

31 31 Major Achievements of OS n Operating Systems are among the most complex pieces of software ever developed n To meet the difficult requirements of multiprogramming and time sharing, there have been 5 major achievements by OS: u Processes and threads u Memory management u Information protection and security u Scheduling and resource management u System structure

32 32 Process n Introduced to obtain a systematic way of monitoring and controlling pgm execution n A process is an executable program with: u associated data (variables, buffers…) u execution context: i.e., all the information that F the CPU needs to execute the process content of the processor registers F the OS needs to manage the process: priority of the process the event (if any) after which the process is waiting other data (that we will introduce later)

33 n Fundamental to the structure of operating systems A process can be defined as: a program in execution an instance of a running program the entity that can be assigned to, and executed on, a processor a unit of activity characterized by a single sequential thread of execution, a current state, and an associated set of system resources

34 34 A simple implementation of processes n The process index register contains the index into the process list of the currently executing process (B) n A process switch from B to A consist of storing (in memory) B’s context and loading (in CPU registers) A’s context n A data structure that provides flexibility (to add new features)

35 n The OS has five principal storage management responsibilities: process isolation automatic allocation and management support of modular programming protection and access control long-term storage

36 36 Memory Management n The key contribution is virtual memory n It allows programs to address memory from a logical point of view without regard to the amount that is physically available n While a program is running only a portion of the program and data is kept in (real) memory n Other portions are kept in blocks on disk u the user has access to a memory space that is larger than real memory

37 37 Virtual Memory Concepts

38 38 Virtual Memory n All memory references made by a program are to virtual memory which can be either u a linear address space u a collection of segments (variable-length blocks) n The hardware (mapper) must map virtual memory address to real memory address n If a reference is made to a virtual address not in memory, then u (1) a portion of the content of real memory is swapped out to disk u (2) the desired block of data is swapped in

39 39 File System n Implements long-term store (often on disk) n Information stored in named objects called files u a convenient unit of access and protection for OS n Files (and portions) may be copied into virtual memory for manipulation by programs

40 40 Security and Protection n Access control to resources u forbid intruders (unauthorized users) to enter the system u forbid user processes to access resources which they are not authorized to

41 41 Scheduling and Resource Management n Differential responsiveness u discriminate between different classes of jobs n Fairness u give equal and fair access to all processes of the same class n Efficiency u maximize throughput, minimize response time, and accommodate as many users as possible

42 42 Key Elements for Scheduling n OS maintains queues of processes waiting for some resource u Short term queue of processes in memory ready to execute F The dispatcher (short term scheduler) decides who goes next u Long term queue of new jobs waiting to use the system F OS must not admit too many processes u A queue for each I/O device consisting of processes that want to use that I/O device

43 43 Key Elements for Scheduling (cont’d)

44 44 System Structure n Because of it’s enormous complexity, we view the OS system as a series of levels n Each level performs a related subset of functions n Each level relies on the next lower level to perform more primitive functions n Well defined interfaces: one level can be modified without affecting other levels n This decomposes a problem into a number of more manageable sub problems

45 45 Characteristics of Modern Operating Systems n New design elements were introduced recently n New hardware development u multiprocessor machines u high-speed networks u faster processors and larger memory n New software / application needs u multimedia applications u Internet and Web access u Client/Server applications

46 46 Microkernel architecture n Only a few essential functions in the kernel u primitive memory management (address space) u Interprocess communication (IPC) u basic scheduling n Other OS services are provided by processes running in user mode (servers) u device drivers, file system, virtual memory… n More flexibility, extensibility, portability… n A performance penalty by replacing service calls with message exchanges between process...

47 47 Multithreading n A process is a collection of one or more threads that can run simultaneously n Useful when the application consists of several tasks that do not need to be serialized n Gives the programmer a greater control over the timing of application-related events n All threads within the same process share the same data and resources and a part of the process’s execution context n It is easier to create or destroy a thread or switch among threads (of the same process) than to do these with processes

48 48 Distributed Systems n Distributed operating systems u Provides the illusion of a single main memory space and single secondary memory space

49 49 Symmetric Multiprocessing (SMP) n A computer with multiple processors n Each processor can perform the same functions and share same main memory and I/O facilities (symmetric) n The OS schedule processes/threads across all the processors (real parallelism) n Existence of multiple processors is transparent to the user. n Incremental growth: just add another CPU (at least in theory). n Robustness: a single CPU failure does not halt the system, only the performance is reduced.

50 50 Example of parallel execution on SMP

51 Quiz 2-3 51 n Name the main difference between multiprogramming and multiprocessing n True or False n Multiprocessing generally implies multiprogramming n Multiprogramming generally implies multiprocessing

52 Quiz 2-3 52 n Micorkernel systems: a. What extra “weight” (features) do they usually remove? b. What are the main advantages? c. What is the main cost?

53 n Virtualization u enables a single PC or server to simultaneously run multiple operating systems or multiple sessions of a single OS u a machine can host numerous applications, including those that run on different operating systems, on a single platform u host operating system can support a number of virtual machines (VM) each has the characteristics of a particular OS and, in some versions of virtualization, the characteristics of a particular hardware platform

54 Virtual Memory Concept


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