1. Chapter 3: Operating-System Structures
System Components
Operating System Services
System Calls
Communication Models
Operating System Structures

2. Common System Components
Process Management
Main Memory Management
File Management
Secondary Storage Management
I/O System Management
Networking
Protection System

3. Process Management
A process is a program in execution. It is a unit of work within the system. Program is a passive entity (content of a file stored on the disk), process is an active entity (with a program counter specifying the next instruction to execute).
A process needs certain resources, including CPU time, memory, files, and I/O devices, to accomplish its task.
The operating system is responsible for the following activities in connection with process management.
Process creation and deletion.
process suspension and resumption.
Provision of mechanisms for:
process synchronization
process communication
Typically system has many processes, some user(execute user code), some operating system(execute system code), running concurrently on one or more CPUs
Concurrency by multiplexing the CPUs among the processes / threads

4. Process Management Activities
The operating system is responsible for the following activities in connection with process management:
Creating and deleting both user and system processes
Suspending and resuming processes
Providing mechanisms for process synchronization
Providing mechanisms for process communication
Providing mechanisms for deadlock handling

5. Process State Diagram dispatch New Ready Running admit time-out
release
activate
event
wait
Exit
Suspend
Blocked
suspend
Operating System Concepts

6. Main-Memory Management
Memory is a large array of words or bytes, each with its own address. Memory is a repository of quickly accessible data shared by the CPU and I/O devices.
To execute a program (or part) all of the instructions must be in memory
All (or part) of the data that is needed by the program must be in memory.
Main memory is a volatile storage device. It loses its contents in the case of system failure.
Memory management determines what is in memory and when
Optimizing CPU utilization and computer response to users
Memory management activities:
Keeping track of which parts of memory are currently being used and by whom
Deciding which processes (or parts of processes) and data to move into and out of memory
Allocating and deallocating memory space as needed

7. File Management
OS provides uniform, logical view of information storage
Abstracts physical properties to logical storage unit - file
A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data.
Each medium is controlled by device (i.e., disk drive, tape drive).
Varying properties include access speed, capacity, data-transfer rate, access method (sequential or random).
File-System management
Files usually organized into directories
Access control on most systems to determine who can access and how (read, write, append)
OS activities include
Creating and deleting files and directories
Primitives to manipulate(change name, type etc.) files and directories
Mapping files onto secondary storage
Backup files onto stable (non-volatile) storage media

8. Secondary-Storage Management
Since main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory.
Usually disks used to store data and programs that does not fit in main memory or data that must be kept for a “long” period of time.
The operating system is responsible for the following activities in connection with disk management:
Free space management
Storage allocation
Disk scheduling

9. Performance of Various Levels of Storage
Movement between levels of storage hierarchy can be explicit or implicit

10. Migration of data “A” from Disk to Register
Multitasking environments must be careful to use most recent value, no matter where it is stored in the storage hierarchy
Multiprocessor environment must provide cache coherency in hardware such that all CPUs have the most recent value in their cache
Distributed environment situation even more complex
Several copies of a datum can exist

11. I/O Subsystem
One purpose of OS is to hide peculiarities(characteristics) of hardware devices from the user (only device driver knows peculiarities of the specific device)
I/O subsystem responsible for
Memory management of I/O including buffering (storing data temporarily while it is being transferred), caching (storing parts of data in faster storage for performance), spooling (the overlapping of output of one job with input of other jobs)
General device-driver interface
Drivers for specific hardware devices

12. Networking (Distributed Systems)
A distributed system is a collection of processors that do not share memory or a clock. Each processor has its own local memory and clock.
The processors in the system are connected through a communication network.
Communication takes place using protocols.
A distributed system provides user access to various system resources.
Access to a shared resource allows:
Computation speed-up
Increased data availability
Enhanced reliability

13. Protection and Security
Protection – any mechanism for controlling access of processes or users to resources defined by the OS
Security – defense of the system against internal and external attacks
Huge range, including denial-of-service, worms, viruses, identity theft, theft of service
Systems generally first distinguish among users, to determine who can do what
User identities (user IDs, security IDs) include name and associated number, one per user
User ID then associated with all files, processes of that user to determine access control
Group identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, thread

14. 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 an user interface (UI).
Varies between Command-Line-Interface (CLI), Graphics User Interface (GUI), Batch (commands and directives to control those command are entered into files, and those files are executed)
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

15. Operating System Services (Cont.)
One set of operating-system services provides functions that are helpful to the user (Cont.):
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.
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 programs
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

16. Operating System Services (Cont.)
Another set of OS functions exists for ensuring the efficient operation of the system itself via resource sharing
Resource allocation - When multiple users or multiple jobs running concurrently, resources must be allocated to each of them
Many types of resources - CPU cycles, main memory, file storage, I/O devices.
Accounting - To keep track of which users use how much and what kinds of computer resources
Protection and security - The owners of information stored in a multiuser 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

17. A View of Operating System Services

18. Note that the system-call names used throughout this text are generic
System Calls
Programming interface to the services provided by the OS(an interface between a running program and 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)
Note that the system-call names used throughout this text are generic

19. 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 the 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)

20. API – System Call – OS Relationship

21. System Call Parameter Passing
Often, more information is required than simply identity of desired system call
Exact type and amount of information vary according to OS and call
Three general methods used to pass parameters to the OS
Simplest: pass the parameters in registers
In some cases, may be more parameters than registers
Parameters stored in a block, or table, in memory, and address of block passed as a parameter in a register
This approach taken by Linux and Solaris
Parameters placed, or pushed, onto the stack by the program and popped off the stack by the operating system
Block and stack methods do not limit the number or length of parameters being passed

22. Parameter Passing via Table

23. Examples of Windows and Unix System Calls

24. Standard C Library Example
C program invoking printf() library call, which calls write() system call

25. Communication Models
Communication may take place using either message passing or shared memory.
Message Passing
Shared Memory

26. Operating System Structures (reading assignment)
General-purpose OS is very large program
Various ways to structure ones
Simple structure – MS-DOS
More complex -- UNIX
Layered – an abstrcation
Microkernel -Mach

27. Simple Structure -- MS-DOS
MS-DOS – written to provide the most functionality in the least space
Not divided into modules
Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated

28. Non Simple Structure -- UNIX
UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts
Systems programs
The kernel
Consists of everything below the system-call interface and above the physical hardware
Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level

29. Traditional UNIX System Structure
Beyond simple but not fully layered

30. Layered Approach
The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface.
With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers

31. Microkernel System Structure
Moves as much from the kernel into user space
Mach example of microkernel
Mac OS X kernel (Darwin) partly based on Mach
Communication takes place between user modules using message passing
Benefits:
Easier to extend a microkernel
Easier to port the operating system to new architectures
More reliable (less code is running in kernel mode)
More secure
Detriments:
Performance overhead of user space to kernel space communication

32. Microkernel System Structure

33. Modules
Many modern operating systems implement loadable kernel modules
Uses object-oriented approach
Each core component is separate
Each talks to the others over known interfaces
Each is loadable as needed within the kernel
Overall, similar to layers but with more flexible
Linux, Solaris, etc

34. Solaris Modular Approach

35. Hybrid Systems
Most modern operating systems are actually not one pure model
Hybrid combines multiple approaches to address performance, security, usability needs
Linux and Solaris kernels in kernel address space, so monolithic, plus modular for dynamic loading of functionality
Windows mostly monolithic, plus microkernel for different subsystem personalities
Apple Mac OS X hybrid, layered, Aqua UI plus Cocoa programming environment
Below is kernel consisting of Mach microkernel and BSD Unix parts, plus I/O kit and dynamically loadable modules (called kernel extensions)

36. Mac OS X Structure

37. iOS Apple mobile OS for iPhone, iPad
Structured on Mac OS X, added functionality
Does not run OS X applications natively
Also runs on different CPU architecture (ARM vs. Intel)
Cocoa Touch Objective-C API for developing apps
Media services layer for graphics, audio, video
Core services provides cloud computing, databases
Core operating system, based on Mac OS X kernel

38. Android Developed by Open Handset Alliance (mostly Google)
Open Source
Similar stack to IOS
Based on Linux kernel but modified
Provides process, memory, device-driver management
Adds power management
Runtime environment includes core set of libraries and Dalvik virtual machine
Apps developed in Java plus Android API
Java class files compiled to Java bytecode then translated to executable than runs in Dalvik VM
Libraries include frameworks for web browser (webkit), database (SQLite), multimedia, smaller libc

39. Android Architecture

40. System Boot
When power initialized on system, execution starts at a fixed memory location
Firmware ROM used to hold initial boot code
Operating system must be made available to hardware so hardware can start it
Small piece of code – bootstrap loader, stored in ROM or EEPROM locates the kernel, loads it into memory, and starts it
Bootstrap program initializes all aspects of the system, from CPU registers to device controller to memory contents.
Common bootstrap loader, GRUB, allows selection of kernel from multiple disks, versions, kernel options
Kernel loads and system is then running(it can start providing services to the system and its users).