OS - Introduction Ezio Bartocci Institute for Computer Engineering

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1 TECHNISCHE UNIVERSITÄT WIEN Fakultät für Informatik Cyber-Physical Systems Group OS - Introduction Ezio Bartocci Institute for Computer Engineering ezio.bartocci@tuwien.ac.at

2 Operative System What is it?

3 Main objectives Convenience: An OS makes a computer more convenient to use Efficiency: An OS allows the computer system resources to be used in an efficient manner. Ability to evolve: An OS should be constructed in a such a way a to permit the effective development, testing, and introduction of new system functions without inferring with service

4 OS as User/Computer Interface Application Progr. Interface Application binary Interface Instruction set architecture Application programs Libraries/utilities Operating systems Execution hardware Software System interconnect (bus) Memory translation Hardware I/O devices and networking Main memory

5 OS as Resource Manager Memory Computer system I/O devices Operative System software I/O controller I/O controller Printers, keyboards, digital camera, etc. Programs and data I/O controller Processor Processor Storage OS Programs Data

6 Outline How did OS arise? What is a OS? Main concepts

7 Evolution of OS

8 OS Evolution Determined by the technological development and the associated cost development - Equipment costs Cost of human labor of expensive equipment Maximize utilization too much labor Comfort and support for users Other factors: troubleshooting, new requirements

in machine code were loaded via the input device Error

9 Serial Processing (late 1940s mid-1950) No OS Direct Programming of Hardware I/O: switches, lamps, card reader, printer Programs in machine code were loaded via the input device Error conditions were indicated by the lights. The output was printed Card Reader

10 Serial Processing (late 1940s mid-1950) Main problems: Error-prone (Solution: subroutines/libraries for I/O) Setup time (Solution: Specialist or monitor) Scheduling time (Solution: automatic scheduler) ü A user might sign up for 1 hour and finish in 45 minutes ü Another user might run into problems not finishing the program for the time requested

11 Simple Batch Systems (1960) Early computers were very expensive Job from Input Device: Read User Program Area Maximizing the processor utilization The wasted time due to scheduling and setup time was unacceptable Interpretation of JCL Commands Execution of Program Continuation in the Monitor

12 Monitor Job Device Drivers Interrupt Processing Job Sequencing JCL Interpreter User Program Area Control command (JCL) + Program Job Control Language (JCL) $JOB $FTN FORTRAN instructions

13 Monitor Memory protection Timer Privileged Instructions Interrupts Problem: either CPU or I/O-System active, rest of the machine does nothing Solution: parallel CPU and I/O activity buffers and I/O Interrupts

14 Multiprogramming Batch System (1965) Problem: no program uses CPU and peripherals permanently or uniformly CPU-intensive Programs (CPU bound) I/O-intensive Programs (I/O bound) Solution: Multiprogramming bzw. Multitasking Read one record from file Execute 100 instructions Write one record from file Total 15 microseconds 1 microsecond 15 microseconds 31 microseconds Percent CPU Utilization = 1/31 = = 3.2 %

15 Multiprogrammed Batch Systems run wait run wait Uniprogramming run A wait run A wait run B wait run B wait run A run B run A run B

16 Multiprogrammed Batch Systems Parallel execution of programs needs new mechanisms, e.g.: Memory management Management of CPU and Resources (Scheduling) Situation (ca. 1970): cheaper computers shall increase productivity of expensive employees

17 Time-Sharing Systems Problem: More users simultaneously share the computer; wait on completion of (Batch) Jobs Solution: Preemptive Scheduling, Priorities Problem: Data and Programs shall be easily available (convenient access) Solution: Filesystem on the computer

18 cheap HW Further Development 1 computer ( PC) per user Computer in office and communiation GUIs Networking Security Growth of the Internet Middleware (Java API, ) Mobility, Voice and Video,... Embedded Computing, Real-Time Comp., Pervasive Computing, real-time, energy management

19 Unix, Mac OS, Windows 1972 "... the number of UNIX installations has grown to 10..." (D. Ritchie, K. Thompson) 1981 MS-DOS auf IBM PC (4000 LOC Assembly) 1983 PC XT : Harddrive, one Directory, 64 Files 1984 Apple Macintosh, Mac OS 1987 MINIX 1990 MS Windows 3.0, auf DOS aufsetzend 1991 first Linux Version 1993 Windows NT (10+ Mio. LOC) multi-tasking, single- / multi-user System

20 What is a OS?

21 OS as Interface Interface between user and hardware virtual machine Resource manager provides programming interface adjusts to the needs of the user

22 Our interests

23 OS - Views End User Programmer User programs / applications OSdesigner Utilities Operating System Computer hardware

24 OS as Service Provider Program execution Program development I/O, file access, network communication Access control Error detection and handling Logging (monitoring, Accounting)

25 OS as Resource Manager no external control instance Uses resources on its own Hands out resources Functionality different to other programs Controls the processor when resources are used and distributes CPU time to processes

26 Main Concepts

27 Abstraction Abstractions undisturbed program execution infinite big memory, files Synchronization und Communication Standard Interface - Portability Manages resources CPU, main memory, hard drive, network access

28 Some Aspects Process Memory management Access protection Scheduling und Resource management System architecture

29 Processes Informal: Program at execution Requirements on process management: Time distribution Signal of events (e.g., I/O) Avoid access conflicts Synchronization

30 Process Processlist Process A b Process B l Main memory i j context Daten Prog. Kontext Daten Prog. Proc.Idx PC Base length further Register Register i b l...

31 Memory Management Virtual Memory Use of memory without consideration of size of physical memory Only parts of running programs are kept in main memory Rest is in secondary memory: addressable memory > main memory

32 Memory Management Views Virtual Processor Virtual memory Files User view Real Processor virt. Adr. Address converter phys. Adr. Main memory Paging, Swapping Secondary storage View of OS-Designer

33 Memory Management Management of memory allocation to processes Memory allocation to processes as required / per need Shift memory content between main and secondary memory Management of access rights Protection and isolation of processes Common memory (Shared Memory) Filesystem

34 Data protection and security Access Control Who is allowed to use a resource? Allowed operations Information flow control Authenticity source of information Integrity no corruption Availability

35 Scheduling, Resource Management Allocation of CPU time and resources to processes Efficiency Fairness Lifeness...

36 System Architecture Layers Every layer implement a functionality Upper layers use services of lower layers Modular setup Managable parts with specific functionality defined Interfaces: modules can be changed without interferences

37 System Architecture Name Object single processor Prozessor-HW Virtual memory Secondary memory primitive Processes Pages, segments Data blocks and channels Processes, Ready list, Semaphores 4 Interrupts Interrupt handlers 3 Procedures Prozeduren, Call Stack 2 Instruktionen Eval. Stack, skalar Data, fields 1 circuits Register, Gates, Busses

38 Original Unix-Layers Name Object one or more processors 13 Shell Programming environment 12 User-Prozesse User prozesse 11 Directories Directories 10 Devices Printer, monitor, keyboard 9 Filesystem Files 8 communikation Pipes

39 Device mappings File mappings Anonymous mappings Unix Architecture (SVR4) Virtual memory framework elf exec switch Common Facilities vnode/vfs interface NFS RFS FFS s5fs Disk driver Block device switch Scheduler framework Time-sharing processes Tape driver Streams tty driver System processes

40 Windows Architecture (Ex.) User Mode System Processes Services Applications Environment Subsystems Kernel Mode Executive API I/O Manager File Systems LPC Facility Memory Manager Process Manager Security Ref. Monitor Object Manager Plug n Play Power Manager Window Manager Graphics Dev. Dr. Device Drivers Microkernel Hardware Abstraction Layer (HAL)

41 Recall OS makes computer usable Provides abstraction Process, memory, Communication, Synchronisation Provides portable programming interface Manages resources

42 Outlook Process, Threads Parallelism, Synchronisation (Mutual Exclusion) Deadlock Memory Management (Virtual Memory) Scheduling I/O File Management Security

Operating Systems Overview. Chapter 2

Operating Systems Overview. Chapter 2 Operating Systems Overview Chapter 2 Operating System A program that controls the execution of application programs An interface between the user and hardware Masks the details of the hardware Layers and