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Chapter 6 An Introduction to System Software and Virtual Machines

Chapter 6 An Introduction to System Software and Virtual Machines. 1. Objectives. In this chapter, you will learn about: System software Assemblers and assembly language Operating systems . Objectives. After studying this chapter, students will be able to:

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Chapter 6 An Introduction to System Software and Virtual Machines

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  1. Chapter 6 • An Introduction to System Software and Virtual Machines 1

  2. Objectives In this chapter, you will learn about: • System software • Assemblers and assembly language • Operating systems Invitation to Computer Science, 6th Edition

  3. Objectives After studying this chapter, students will be able to: • Describe the main categories of system tasks • Compare the virtual machine created for the user by system software with the naked machine • Explain the benefits of writing system software in assembly language, rather than machine language • Read and write short assembly language programs • Describe how an assembler translates assembly language programs into machine instructions Invitation to Computer Science, 6th Edition

  4. Objectives (continued) After studying this chapter, students will be able to: • List five key tasks of an operating system, and explain what each is and why it is critical to modern systems • Describe the different generations of operating systems, what the features of each generation were, and how each generation solved a drawback of the previous generation Invitation to Computer Science, 6th Edition

  5. Introduction • A bare or naked machine has no tools or programs to help the user • Write instructions in binary • Write data in binary • Load instructions into memory one cell at a time • Initiate program run • Too difficult for humans to do • We must build an interface to hide the details and make the computer easier to build Invitation to Computer Science, 6th Edition

  6. Interface • Von Neumann computer • “Naked machine” • Hardware without any helpful user-oriented features • Extremely difficult for a human to work with • An interface between the user and the hardware is needed to make a Von Neumann computer usable and people oriented ( like “dashboard” on a car ) Invitation to Computer Science, 6th Edition

  7. Interface • Tasks of the interface • Hide details of the underlying hardware from the user • Present information in a way that does not require in-depth knowledge of the internal structure of the system • Allow easy user access to the available resources • Prevent accidental or intentional damage to hardware, programs, and data Invitation to Computer Science, 6th Edition

  8. Software • Application software • programs primarily for users ( word processors, spreadsheets, databases, presentation graphics, etc.) • System software • primarily used to run the computer (operating system, device drivers, assemblers, compilers ) Invitation to Computer Science, 6th Edition

  9. System Software • System software is the intermediary between the users and hardware • Hides complex internal structure of the Von Neumann architecture • Virtual Machine/Virtual Environment • The set of services and resources created by the software and seen by the user Invitation to Computer Science, 6th Edition

  10. System Software • System software is a collection of programs to • manage resources of the computer • serve as intermediary between user and hardware • System software creates a virtual machine(or virtual environment) that user sees Invitation to Computer Science, 6th Edition

  11. System Software (continued) • Operating system: central system software • Communicates with users • Starts up other system software and applications as needed • Graphical user interface (GUI), often pronounced “gooey” • visual interface to operating system (or other system software/applications) • I/O systems: communicate with various devices Invitation to Computer Science, 6th Edition

  12. 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 packages, or user programs to carry out user requests Invitation to Computer Science, 6th Edition

  13. Types of System Software • User interface • Graphical user interface (GUI) provides graphical control of the capabilities and services of the computer • Language services • Assemblers, compilers, and interpreters • Allow you to write programs in a high-level, user-oriented language, and then execute them Invitation to Computer Science, 6th Edition

  14. Types of System Software • Memory managers • Allocate and retrieve memory space • Information managers • Handle the organization, storage, and retrieval of information on mass storage devices • I/O systems • Allow the use of different types of input and output devices Invitation to Computer Science, 6th Edition

  15. Types of System Software • Scheduler • Keeps a list of programs ready to run and selects the one that will execute next • Utilities • Collections of library routines that provide services either to user or other system routines Invitation to Computer Science, 6th Edition

  16. System Software (continued) • Language services: support high level languages • Memory managers: allocate memory to programs • Information managers: organize mass storage • Scheduler: manage programs waiting to run • Utilities: tools, including program libraries Invitation to Computer Science, 6th Edition

  17. System Software (continued) Naked machine: • Write program in binary • Load instructions one-by-one into memory • Insert start into memory address 0 and push “go” button • Read results from memory one-by-one, in binary Virtual machine: • Write program using text editor in high-level language • Save program to folder • Use translator to convert to binary • Use scheduler to load and run • Use I/O system to print results Invitation to Computer Science, 6th Edition

  18. What’s the Problem with Machine Language? • Written from machine’s view • Complicated, difficult to understand • Program is written, loaded, debugged in binary - no English-like words • Allows only numeric memory addresses • Difficult to read and change • Difficult to create data Invitation to Computer Science, 6th Edition

  19. Assembly Language • Assembly language • Designed to overcome shortcomings of machine languages • Create a more productive, user-oriented environment • Earlier termed second-generation languages • Now viewed as low-level programming languages Invitation to Computer Science, 6th Edition

  20. Assembly Language • Second-generation language • Uses mnemonics to represent machine language opcodes • Uses symbolic memory addresses • Provides data generation operations • Format: label: opcode address --comment Invitation to Computer Science, 6th Edition

  21. Assemblers and Assembly Language • Assembly language • Instructions map one-to-one to machine language • Symbolic op codes (not binary) • Symbolic addresses for instructions and data • Pseudo-ops for data generation and more (data in human-friendly terms) • Assembly = a low-level programming language • Java, C, C++, VB, Python = high-level programming languages Invitation to Computer Science, 6th Edition

  22. Invitation to Computer Science, 6th Edition

  23. Assemblers and Assembly Language • Source program • An assembly language program • Object program • A machine language program • Assembler • Translates source program into an object program Assembly language process: • Source program, in assembly language • Translated by the assembler to • Object program, in machine language • Loader places in memory • Hardware runs Invitation to Computer Science, 6th Edition

  24. Invitation to Computer Science, 6th Edition

  25. Assemblers and Assembly Language (continued) Example Assembly language: NEXTSTEP: LOAD X -- Put X into reg. R label: opcode address field -- comment • Label is optional name for this instruction’s location • Op code mnemonic and address field translate to machine language • Comments are ignored by assembler, just for human use Invitation to Computer Science, 6th Edition

  26. Invitation to Computer Science, 6th Edition

  27. Assemblers and Assembly Language (continued) Advantages over machine code: • Clarity, readability, and maintainability • Can be placed at different locations in memory • Pseudo-op: commands in the program directed to the assembler, not converted to machine instructions • .BEGIN and .END to mark where instructions are • .DATA to mark memory location as holding data: COUNTER: .DATA 0 X: .DATA 12 Invitation to Computer Science, 6th Edition

  28. Examples of Assembly Language Instructions • Assembly language translation LOAD ONE --Put a 1 into register R. STORE X --Store the constant 1 into X : INCREMENT X --Add 1 to Value in memory location X : I: .DATA 0 --The index value. Initially it is 0 ONE: .DATA 1 --The constant 1. Invitation to Computer Science, 6th Edition

  29. Examples of Assembly Language Instructions • Assigns name to address where data is stored • Converts data value to proper binary representation • Example: FIVE: .DATA +5 NEGSEVEN: .DATA -7 LOAD FIVE ADD NEGSEVEN • Arithmetic expression A = B + C – 7 (Assume that B and C have already been assigned values) Invitation to Computer Science, 6th Edition

  30. Examples of Assembly Language Instructions • Assembly language translation .BEGIN LOAD B --Put the value B into register R. ADD C --R now holds the sum (B + C). SUBTRACT SEVEN --R now holds the expression (B + C - 7). STORE A --Store the result into A. : -- Data should be placed after the HALT A: .DATA 0 B: .DATA 0 C: .DATA 0 SEVEN: .DATA 7 --The constant 7 .END Invitation to Computer Science, 6th Edition

  31. Invitation to Computer Science, 6th Edition

  32. Assemblers and Assembly Language Simple examples: x = y + 3 input a and b while a > b do print a a = a – 2 LOAD Y ADD THREE STORE X … -- Data comes after .END X: .DATA 0 -- X is initially 0 Y: .DATA 5 – Y is initially 5 THREE: .DATA 3 –The constant 3 IN A IN B LOOP1: LOAD A A: .DATA 0 COMPARE B B: .DATA 0 JUMPLT LOOP1END TWO: .DATA 2 JUMPEQ LOOP1END OUT A LOAD A SUBTRACT TWO STORE A JUMP LOOP1 LOOP1END: … Invitation to Computer Science, 6th Edition

  33. Example – Summing Numbers • Problem • Read in a sequence of non-negative numbers, one number at a time, and compute a running sum • When you encounter a negative number, print out the sum of the non-negative values and stop Invitation to Computer Science, 6th Edition

  34. Invitation to Computer Science, 6th Edition

  35. Assemblers and Assembly Language Translation and loading: • Assembler translates to machine language • Convert symbolic op codes to binary equivalents • Convert symbolic labels to memory addresses • Perform pseudo-op actions • Write object file containing machine instructions • Loader gets program ready to run • Places instructions in memory • Triggers the hardware to run the program Invitation to Computer Science, 6th Edition

  36. Assemblers and Assembly Language Converting symbolic op codes to binary ones • Assembler maintains a table • Assembler looks up symbolic op codes in the table and substitutes the binary analogue • Use binary search to optimize table lookups

  37. Assemblers and Assembly Language Converting symbolic labels to memory addresses • Assembler needs two passes • looks over assembly code two times • First pass: • Keep a count of how many instructions from the start • Collect symbolic labels and add to symbol tablealong with location counter Invitation to Computer Science, 6th Edition

  38. Invitation to Computer Science, 6th Edition

  39. Assemblers and Assembly Language (continued) • Second pass: • Look up and replace op codes • Substitute label references with location from symbol table • Set up .DATA pseudo-ops with location and binary value • Write instructions to object file Invitation to Computer Science, 6th Edition

  40. Invitation to Computer Science, 6th Edition

  41. Translation and Loading • The object program becomes the input to another piece of software – the loader • The loader reads instructions from the object file and stores them in memory for execution • To do this it reads and address and stores the machine instruction into the specified memory address. • After the instructions are loaded into memory, the loader places the address of the first instruction (0 in our example) into the program counter (PC) . • The computer fetches, decodes and executes the program starting with the instruction, whose address is in the PC. Invitation to Computer Science, 6th Edition

  42. Operating Systems • What is an operating system? • A library of programs that make a computer • Easier to user for the user • Use resources more efficiently • It can also be viewed as: • A Government – making policy and rules • An Environment – in which users write and run programs • A Resource allocator • A Security guard • A Traffic cop • A Wizard – providing “illusions” Invitation to Computer Science, 6th Edition

  43. Purpose of an Operating System • The primary purposes of an Operating System are: • Ease of use for the user • Efficient use of the system resources • Operating system • Waits for requests and activates other system programs to service these requests • System commands • Used to translate, load, and run programs Invitation to Computer Science, 6th Edition

  44. Operating Systems • System commands: - user instructions about what the computer should do Invitation to Computer Science, 6th Edition

  45. Operating Systems (continued) • User interface: user communicates with operating system • Operating system as receptionist and dispatcher • User command  system software scheduled and runrepeat • Text-based: • System commands typed at a prompt in a terminal • Command language must be learned • GUI-based: • System commands by visual/mouse interface Invitation to Computer Science, 6th Edition

  46. GUIs Example of a Graphical User Interface Invitation to Computer Science, 6th Edition

  47. Invitation to Computer Science, 6th Edition

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