Objectives Chapter 6: An Introduction In this chapter, you will learn about: to System Software and System software Virtual Machines Invitation to Computer Science, Assemblers and assembly language C++ Version, Third Edition Operating systems Invitation to Computer Science, C++ Version, Third Edition 2 Introduction Introduction (continued) Von Neumann computer Tasks of the interface “Naked machine” Hide details of the underlying hardware from the Hardware without any helpful user-oriented features user Extremely difficult for a human to work with Present information in a way that does not require An interface between the user and the hardware in-depth knowledge of the internal structure of the is needed to make a Von Neumann computer system usable Invitation to Computer Science, C++ Version, Third Edition 3 Invitation to Computer Science, C++ Version, Third Edition 4 Introduction (continued) System Software: The Virtual Machine Tasks of the interface (continued) System software Acts as an intermediary between users and hardware Allow easy user access to the available resources Creates a virtual environment for the user that hides the actual computer architecture Prevent accidental or intentional damage to hardware, programs, and data Virtual machine (or virtual environment) Set of services and resources created by the system software and seen by the user Invitation to Computer Science, C++ Version, Third Edition 5 Invitation to Computer Science, C++ Version, Third Edition 6 1 Types of System Software System software is a collection of many different programs Operating system Controls the overall operation of the computer Communicates with the user Determines what the user wants Activates system programs, applications Figure 6.1 packages, or user programs to carry out user The Role of System Software requests Invitation to Computer Science, C++ Version, Third Edition 7 Invitation to Computer Science, C++ Version, Third Edition 8 Types of System Software (continued) User interface Graphical user interface (GUI) provides graphical control of the capabilities and services of the computer Language services Assemblers, compilers, and interpreters Figure 6.2 Allow you to write programs in a high-level, user- Types of System Software oriented language, and then execute them Invitation to Computer Science, C++ Version, Third Edition 9 Invitation to Computer Science, C++ Version, Third Edition 10 Types of System Software (continued) Types of System Software (continued) Memory managers Scheduler Allocate and retrieve memory space Keeps a list of programs ready to run and selects Information managers the one that will execute next Handle the organization, storage, and retrieval of information on mass storage devices Utilities I/O systems Collections of library routines that provide services Allow the use of different types of input and output devices either to user or other system routines Invitation to Computer Science, C++ Version, Third Edition 11 Invitation to Computer Science, C++ Version, Third Edition 12 2 Assemblers and Assembly Language: Assembly Language (continued) Assembly Language Assembly languages Machine language Designed to overcome shortcomings of machine Uses binary languages Allows only numeric memory addresses Create a more productive, user-oriented environment Difficult to change Earlier termed second-generation languages Difficult to create data Now viewed as low-level programming languages Invitation to Computer Science, C++ Version, Third Edition 13 Invitation to Computer Science, C++ Version, Third Edition 14 Assembly Language (continued) Source program An assembly language program Object program A machine language program Assembler Figure 6.3 Translates a source program into a corresponding The Continuum of Programming Languages object program Invitation to Computer Science, C++ Version, Third Edition 15 Invitation to Computer Science, C++ Version, Third Edition 16 Assembly Language (continued) Advantages of writing in assembly language rather than machine language Use of symbolic operation codes rather than numeric (binary) ones Use of symbolic memory addresses rather than numeric (binary) ones Figure 6.4 Pseudo-operations that provide useful user- The Translation/Loading/Execution Process oriented services such as data generation Invitation to Computer Science, C++ Version, Third Edition 17 Invitation to Computer Science, C++ Version, Third Edition 18 3 Examples of Assembly Language Code (continued) Algorithmic operations Set the value of i to 1 (line 2). : Add 1 to the value of i (line 7). Figure 6.6 Structure of a Typical Assembly Language Program Invitation to Computer Science, C++ Version, Third Edition 19 Invitation to Computer Science, C++ Version, Third Edition 20 Examples of Assembly Language Examples of Assembly Language Code (continued) Code (continued) Assembly language translation Arithmetic expression LOAD ONE --Put a 1 into register R. A = B + C – 7 STORE I --Store the constant 1 into i. : (Assume that B and C have already been assigned INCREMENT I --Add 1 to memory location i. values) : I: .DATA 0 --The index value. Initially it is 0. ONE: .DATA 1 --The constant 1. Invitation to Computer Science, C++ Version, Third Edition 21 Invitation to Computer Science, C++ Version, Third Edition 22 Examples of Assembly Language Examples of Assembly Language Code (continued) Code (continued) Assembly language translation Problem LOAD B --Put the value B into register R. ADD C --R now holds the sum (B + C). Read in a sequence of non-negative numbers, SUBTRACT SEVEN --R now holds the expression (B + C - 7). one number at a time, and compute a running STORE A --Store the result into A. : --These data should be placed after the sum HALT. A: .DATA 0 When you encounter a negative number, print out B: .DATA 0 the sum of the non-negative values and stop C: .DATA 0 SEVEN: .DATA 7 --The constant 7. Invitation to Computer Science, C++ Version, Third Edition 23 Invitation to Computer Science, C++ Version, Third Edition 24 4 Figure 6.7 Figure 6.8 Assembly Language Program to Algorithm to Compute the Sum of Numbers Compute the Sum of Nonnegative Numbers Invitation to Computer Science, C++ Version, Third Edition 25 Invitation to Computer Science, C++ Version, Third Edition 26 Translation and Loading Translation and Loading (continued) Before a source program can be run, an Assembler tasks assembler and a loader must be invoked Convert symbolic op codes to binary Assembler Translates a symbolic assembly language Convert symbolic addresses to binary program into machine language Perform assembler services requested by the Loader pseudo-ops Reads instructions from the object file and stores them into memory for execution Put translated instructions into a file for future use Invitation to Computer Science, C++ Version, Third Edition 27 Invitation to Computer Science, C++ Version, Third Edition 28 Operating Systems Functions of an Operating System Five most important responsibilities of the System commands operating system Carry out services such as translate a program, load a program, run a program User interface management Types of system commands Program scheduling and activation Lines of text typed at a terminal Control of access to system and files Menu items displayed on a screen and selected with a mouse and a button: point-and-click Efficient resource allocation Examined by the operating system Deadlock detection and error detection Invitation to Computer Science, C++ Version, Third Edition 29 Invitation to Computer Science, C++ Version, Third Edition 30 5 The User Interface Operating system Waits for a user command If command is legal, activates and schedules the appropriate software package User interfaces Figure 6.15 Text-oriented User Interface Responsibility of the Operating System Graphical Invitation to Computer Science, C++ Version, Third Edition 31 Invitation to Computer Science, C++ Version, Third Edition 32 System Security And Protection Efficient Allocation Of Resources The operating system must prevent The operating system ensures that Non-authorized people from using the computer Multiple tasks of the computer may be underway at one time User names and passwords Processor is constantly busy Legitimate users from accessing data or programs Keeps a “queue” of programs that are ready to run they are not authorized to access Whenever processor is idle, picks a job from the Authorization lists queue and assigns it to the processor Invitation to Computer Science, C++ Version, Third Edition 33 Invitation to Computer Science, C++ Version, Third Edition 34 The Safe Use Of Resources Historical Overview of Operating Systems Development Deadlock Two processes are each holding a resource the First generation of system software (roughly other needs 1945–1955) Neither process will ever progress No operating systems The operating system must handle deadlocks Deadlock prevention Assemblers and loaders were almost the only Deadlock recovery system software provided Invitation to Computer Science, C++ Version, Third Edition 35 Invitation to Computer Science, C++ Version, Third Edition 36 6 Historical Overview of Operating Systems Development (continued) Second generation of system software (1955– 1965) Batch operating systems Ran collections of input programs one after the other Included a command language Figure 6.18 Operation of a Batch Computer System Invitation to Computer Science, C++ Version,