1. Operating-System Structures
Operating System & its purpose
Operating Systems lead to new Hardware Features
System Components
System Services
System Calls
System Programs

2. Operating System Operating System Purpose
An Operating System is a program that acts as an intermediary between a user of a computer and the computer hardware
Purpose
Operating System provide an environment in which a user can execute programs

3. How Operating System lead to new Hardware Features
Simple Batch System
Large machine run from a console,
Input through card reader or tape
Out put through line printers
Multi-programmed Batched System
The OS keeps several jobs in memory at a time
Time-Sharing or Multitasking Systems
Switching between jobs, user may interact
Personal Computers Systems

4. How Operating System led to new Hardware Features
Parallel or Multi-processor Systems
More than one processor, sharing the computer bus, clock, memory and peripheral devices – Tightly coupled systems
Distributed Systems
Distribute computation among several processors, do not share memory or clock, every processor has its own local memory
Real Time Systems
When there is rigid requirement on the operation of a processor or flow of data, control devices

5. System Components
Designing a OS is critical task depends on defining goals
Different point of views of OS
What services OS provide & how these are provide
Interface it make available to user and programmer
Sub system components integration & their interactions
What are the various methodologies for designing such systems

6. System Components Process Management Main Memory Management
File Management
I/O System Management
Secondary Storage Management
Networking
Protection system
Command Interpreter System

7. System Components Process Management
A process is a set of instruction or program in execution
Batch, system task (spooling output to a printer)
Process needs certain resources including CPU time, memory and I/O devices to accomplish its tasks
OS is responsible for the following activities w.r.t process management
Creation and deletion of user and system program
Suspension and resumption of process
Provision of mechanism for process communication and also for deadlock handling

8. System Components Main Memory Management
Central to operation of computer system
Quickly & Directly accessible
CPU read and write data into main memory
When retrieval from hard disk is required – first data loaded into main memory by I/O calls
OS is responsible for the following activities w.r.t Main Memory Management
Keep track of which part of memory are currently being used & by whom
Decide which process are to be loaded into memory when memory space is available
Allocate or de-allocate memory space as needed

9. System Components File Management
Abstract form of physical properties of its storage devices to define logical storage
Collection of related information/ data which may numeric or alphabetic
Visible component of an OS stored in magnetic disk or tapes with different physical organization depends on speed, capacity, rate etc
OS is responsible for the following activities w.r.t Main File Management
Creation or deletion of files/ directories
Manipulating files and directories
Mapping of files onto secondary storage
Back up of files on to non volatile media

10. System Components I/O System Management I/O System consists of
OS purpose is to hide complexities from user
I/O complexities are hidden from bulk of OS itself by the I/O subsystem
I/O System consists of
Buffering, caching and spooling
A general device driver interface
Driver for specific hardware devices

11. System Components Secondary Storage Management
Permanent storage
All data is stored
Computer system must provide for permanent storage as back up for RAM
OS is responsible for the following activities w.r.t Secondary Storage Management
Free space management
Storage allocation
Disk scheduling

12. System Components Networking
Distributed system is collection of process do not share memory, devices, clock
Each process has its own memory and clock
LAN, WAN configuration, Homogenous/ Heterogeneous environment
Processors connected through high speed line or telephone lines
Consider routing, connection strategies & securities
Communication and data sharing is made

13. System Components Protection system
Refers to mechanism for controlling the access of program, process or users to the resources defined by a computer system
Computer system have multiple users
Allow concurrent execution of programs
Protection is required
E.g Files, Memory segments, CPU, Other resources
Only authorize persons can access
Improve reliability - make system healthy

14. System Components Command Interpreter system
Interface between user & system
MS DoS - Kernal
Windows GUI, Mouse , Key board - Shell

15. Operating System Services
Objective
To describe the services an operating system provides to users, processes, and other systems
To discuss the various ways of structuring an operating system
To explain how operating systems are installed and customized and how they boot

16. Operating System Services
User interface - Almost all operating systems have a user interface (UI)
Varies between Command-Line (CLI), Graphics User Interface (GUI)
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. Obviously, programs need to read and write files and directories, create and delete them, search them, list file Information, permission management.

17. 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

18. Operating System Services (Cont.)
Resource allocation - When multiple users or multiple jobs running concurrently, resources must be allocated to each of them
Many types of resources - Some (such as CPU cycles, main memory, and file storage) may have special allocation code, others (such as I/O devices) may have general request and release code.
Accounting - To keep track of which users use how much and what kinds of computer resources

19. Operating System Services (Cont.)
Protection and security - The owners of information stored in a multi-user or networked computer system may want to control use of that information, concurrent processes should not interfere with each other
Protection involves ensuring that all access to system resources is controlled
Security of the system from outsiders requires user authentication, extends to defending external I/O devices from invalid access attempts
If a system is to be protected and secure, precautions must be instituted throughout it. A chain is only as strong as its weakest link.

20. User Operating System Interface - GUI
Many systems now include both CLI and GUI interfaces
Microsoft Windows is GUI with CLI “command” shell
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 or folder

21. System Calls
System calls are the 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 Program Interface (API) rather than direct system call use
Three most common APIs are Win32 API for Windows, POSIX API for all versions of UNIX, Linux, and Mac OS, and Java API for the Java virtual machine (JVM)

22. Example of Standard API
Consider the ReadFile() function in the
Win32 API—a function for reading from a file
A description of the parameters passed to ReadFile()
HANDLE file—the file to be read
LPVOID buffer—a buffer where the data will be read into and written from
DWORD bytesToRead—the number of bytes to be read into the buffer
LPDWORD bytesRead—the number of bytes read during the last read
LPOVERLAPPED ovl—indicates if overlapped I/O is being used

23. API – System Call – OS Relationship

24. Types of System Calls Process control File manipulation
End, Abort, Load, Execute
Create/ Terminate process
Get/Set process attributes
Wait event, Signal event
Allocate & Free memory
File manipulation
Create/ Delete file
Open, Close, Read, Write
Get/ Set File attribute
Device manipulation
Request/ Release Device
Read, Write, Reposition
Logically attach or detach devices

25. Types of System Calls Information maintenance Get/ Set time or date
Get/ Set System data
Get/ Set process, file, or device attribute
Communications
Create/ Delete communication connection
Send/ Receive messages
Transfer status information
Attach or detach remote devices

26. Steps in Making a System Call
There are 11 steps in making the system call
read (fd, buffer, nbytes)

27. System Programs
System programs provide a convenient environment for program development and execution. Some of them are simply user interfaces to system calls; others are considerably more complex
The can be divided into:
File manipulation
Status information
File modification
Programming language support
Program loading and execution
Communications
Application programs

28. System Programs (cont’d)
File manipulation –
Create, delete, copy, rename, print, dump, list, and generally manipulate files and directories
Status information
Some ask the system for info - date, time, amount of available memory, disk space, number of users
Others provide detailed performance, logging, and debugging information
Typically, these programs format and print the output to the terminal or other output devices

29. System Programs (cont’d)
File modification
Text editors to create and modify files
Special commands to search contents of files or perform transformations of the text
Programming-language support
Compilers, assemblers, debuggers and interpreters sometimes provided

30. System Programs (cont’d)
Program loading and execution
Absolute loaders, , linking, and execution, debugging systems for higher-level and machine language
Communications
Provide the mechanism for creating virtual connections among processes, users, and computer systems
Allow users to send messages to one another’s screens, browse web pages, send electronic-mail messages, log in remotely, transfer files from one machine to another
Application Programs
OS provide programs that solve common problem or perform common operations
Web browser, word processor, spread sheets, databases