Operating System Structures: Services, Interfaces, System Calls, and Programs, Slides of Software Engineering

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Chapter 2: Operating-System

Structures

Chapter 2: Operating-System Structures

• (^) Operating System Services
• (^) User Operating System Interface
• (^) System Calls
• (^) Types of System Calls
• (^) System Programs
• (^) Operating System Design and Implementation
• Operating System Structure
• (^) Operating System Debugging
• (^) Operating System Generation
• (^) System Boot

Operating System Services

• (^) Operating systems provide an environment for execution of programs and services to programs and users
• (^) One set of operating-system services provides functions that are helpful to the user:
  • (^) User interface - Almost all operating systems have a user interface ( UI ).
    • (^) Varies between Command-Line (CLI) , Graphics User Interface (GUI) , Batch
  • (^) Program execution - The system must be able to load a program into memory and to run that program, end execution, either normally or abnormally (indicating error)
  • (^) I/O operations - A running program may require I/O, which may involve a file or an I/ O device
  • (^) File-system manipulation - The file system is of particular interest. Programs need to read and write files and directories, create and delete them, search them, list file Information, permission management.

Operating System Services (Cont.)

• (^) Communications – Processes may exchange information, on the same computer or between computers over a network - (^) Communications may be via shared memory or through message passing (packets moved by the OS)
• Error detection – OS needs to be constantly aware of possible errors
  • (^) May occur in the CPU and memory hardware, in I/O devices, in user program
  • (^) For each type of error, OS should take the appropriate action to ensure correct and consistent computing
  • (^) Debugging facilities can greatly enhance the user’s and programmer’s abilities to efficiently use the system

A View of Operating System Services

User Operating System Interface - CLI

• (^) CLI or command interpreter allows direct command entry
  • Sometimes implemented in kernel, sometimes by systems program
  • (^) Sometimes multiple flavors implemented – shells
  • (^) Primarily fetches a command from user and executes it
    • Sometimes commands built-in, sometimes just names of programs
      • (^) If the latter, adding new features doesn’t require shell modification

User Operating System Interface - GUI

• (^) User-friendly desktop metaphor interface
  • Usually mouse, keyboard, and monitor
  • Icons represent files, programs, actions, etc
  • (^) Various mouse buttons over objects in the interface cause various actions (provide information, options, execute function, open directory (known as a folder )
  • (^) Invented at Xerox PARC
• (^) Many systems now include both CLI and GUI interfaces
  • (^) Microsoft Windows is GUI with CLI “command” shell
  • (^) Apple Mac OS X is “Aqua” GUI interface with UNIX kernel underneath and shells available
  • (^) Unix and Linux have CLI with optional GUI interfaces (CDE, KDE, GNOME)

Touchscreen Interfaces

Touchscreen devices require new

interfaces

Mouse not possible or not desired Actions and selection based on gestures Virtual keyboard for text entry

System Calls

• (^) Programming interface to the services provided by the OS
• (^) Typically written in a high-level language (C or C++)
• (^) Mostly accessed by programs via a high-level Application

Programming Interface (API) rather than direct system call use

• (^) Three most common APIs are Win32 API for Windows, POSIX API

for POSIX-based systems (including virtually all versions of UNIX,

Linux, and Mac OS X), and Java API for the Java virtual machine

(JVM)

• (^) Why use APIs rather than system calls?

(Note that the system-call names used throughout this text are

generic)

Example of System Calls

• (^) System call sequence to copy the contents of one file to another file

System Call Implementation

• (^) Typically, a number associated with each system call
  • (^) System-call interface maintains a table indexed according to these numbers
• The system call interface invokes intended system call in OS kernel

and returns status of the system call and any return values

• (^) The caller need know nothing about how the system call is

implemented

• Just needs to obey API and understand what OS will do as a result call
• Most details of OS interface hidden from programmer by API
  • (^) Managed by run-time support library (set of functions built into libraries included with compiler)

API – System Call – OS Relationship

Parameter Passing via Table

Types of System Calls

• (^) Process control
  • end, abort
  • load, execute
  • (^) create process, terminate process
  • (^) get process attributes, set process attributes
  • (^) wait for time
  • (^) wait event, signal event
  • allocate and free memory
  • Dump memory if error
  • Debugger for determining bugs, single step execution
  • (^) Locks for managing access to shared data between processes