Operating System Structures

Operating System Structures

• Chapter two covers operating-system structures.
• The chapter will also cover operating system services, user operating system interface, system calls, system programs
• Also operating system design and implementation, operating system structures, virtual machines, operating system debugging and generation and system boot

Objectives

• To describe OS services provided to users, processes, and other systems.
• To discuss how to structure an operating system.
• To explain OS installation, customization, and booting procedures.

Operating System Services

• Functions helpful to the user are provided by one set of operating-system services.
• Operating Systems supply different kinds of services to both users and programs.
• Application programs that run within the operating system can execute freely within an environment.
• The OS gives users services to run programs conveniently.

User Interface

• Almost all operating systems include a user interface (UI).
• The UI can vary between Command-Line (CLI), Graphics User Interface (GUI), and Batch (Non-Interactive).

Program Execution

• The OS must be able to load a program into memory and to run that program.
• Ending execution of programs ends either normally or abnormally (indicating an error).

I/O Operations

• A running program might require I/O, involving either a file or an I/O device.
• A user cannot directly control I/Os, the OS controls them.

File-System Manipulation

• Working with a file system is pivotal.
• Programs are required to read, write, create, and delete files and directories.
• Also need to search and list file information, including managing permissions aka access restrictions.

Communications

• Take place between processes, the program that performs the processes in execution.
• Processes might need to communicate and synchronize their execution effectively.
• Processes can communicate within the same computer or over a network.

Error Detection

• An OS must always be aware of possible errors in the CPU, memory hardware, I/O devices, and user programs.
• For each error type, the OS needs to respond appropriately to ensure consistent computing.
• Debugging facilities can greatly enhance the user's and programmer's abilities to efficiently use the systems.

Resource Allocation

• When multiple users/jobs are running concurrently; resources need to be allocated to each of them.
• Certain resources such as CPU cycles, main memory, and file storage may require specialized allocation code.
• Others like I/O devices could use general request and release code.
• Processes shouldn't have to perpetually wait for unavailable resources, nor exclusively hold resources without releasing.

Accounting

• Accounting tracks user usage, including the type and amount of computer resources used.

Protection and Security

• Protection manages all access to system resources.
• Concurrent processes should never interfere with each other
• Information owners in multi-user/networked systems have a degree of control over their data.
• Security secures the OS, requiring user authentication and defense against invalid I/O access attempts from outsiders.
• To maintain system security, precautions must be implemented throughout the entire system.
• Any invalid access attempts must be recorded so the user can improve the system.

Operating System Interface - CLI

• Command Line Interface (CLI) or command interpreter allows direct command entry.
• The CLI is sometimes implemented in the kernel or by systems programs.
• Multiple CLI flavors can be implemented as "shells" for each flavor fetch commands and executes them.
• Some commands are built-in; others are just program names.
• New features with shell modification aren't required for the latter.

Operating System Interface - GUI

• User-friendly desktop metaphor interface.
• Usually uses a mouse, keyboard, and monitor.
• Icons represent files, programs, and actions.
• Mouse buttons pressed over interface objects cause varied actions like option displays, function executions, and directory openings.
• Xerox PARC invented the GUI.

Mixed Interfaces

• Many systems now offer both CLI and GUI.
• Microsoft Windows is a GUI utilizing a CLI "command" shell.
• Apple Mac OS X features an "Aqua" GUI interface with a UNIX kernel and available shells, allowing flexibility
• Solaris offers CLI with optional GUI interfaces, such as Java Desktop and KDE.

System Calls

• System calls are the programming interface to the services the OS provides.
• Also perform Context Switching: User Mode <-> Kernel Mode
• It is how a computer program requests a service from the kernel.
• System calls are commonly written in high-level languages (C or C++).
• Programs mostly use a high-level Application Program Interface (API) instead of calling system calls directly.
• Win32 API for Windows, POSIX API for POSIX-based systems (UNIX, Linux, and Mac OS X), and Java API for the Java virtual machine (JVM) include the three most common APIs.
• APIs rather than systems calls should be used.

Example of Standard API - Win32

• The sample function for the Win32 API is ReadFile().
• API parameters passed to ReadFile() are a HANDLE file (file to be read).
• Also, LPVOID buffer (buffer to read/write data), DWORD bytesToRead (bytes in buffer).
• LPDWORD bytesRead is the number of bytes read during last read.
• LPOVERLAPPED ovl — shows that, the overlapped I/O is in use

System Call Implementation

• System calls have a number associated with each.
• The System-call interface uses a table indexed according to these numbers.
• The system call interface invokes the correct system call in the OS kernel and provides any return values or status of calls.
• Callers need to only understand the purposes of results, not execution.
• The API manages a runtime support library and hides the OS interface.

Copying Files

• System calls can be sequenced to complete tasks, like copying the content of one file to another
• Get the input filename and output filename by prompting the system to display it on screen and accepting input
• Open and read files while handling errors, then proceed to close them

Standard C Library Example

• Invoking the printf() library call in a C program subsequently triggers the write() system call.
• The standard C library operates in user mode which then uses write () to run write() system call which then transits instructions back

System Call Parameter Passing

• More data is required than identifying the desired system call, and so are passed by the OS.
• Passing the parameters in registers is the simplest method, however, there may be cases where parameters exceed available registers.
• Storing parameters in a memory block or table before passing the block's address as register parameter is one method that Linux and Solaris uses
• Parameters can get placed (pushed) onto program stack and allow Operating system to pop them off it.
• Parameter length are not limited by block and stack methods in parameter passing

COURSE LEARNING OUTCOMES

• Explain the logical progression of OS development.
• Explain the necessary components and structures of an OS
• Install and customize an OS and write simple shell scripts.
• Also, evaluate various process scheduling and inter-process communication methods.
• Provide an explanation of file-system concepts and operations.
• Kinds of system calls

Types of System Calls

• Process control system calls.
• System calls for file and device management.
• System calls handle the maintenance of information and communications.
• System calls for protection.

Process Control

• Within a system, every current process emerges from another, except the very first.
• New processes originate from a parent process which, designates new releases as the child process.
• Each individual process in the system has a unique process ID, so there are system calls to support this.

File Management System Calls

• Systems support the creation and deletion of files.
• Certain system calls are need to create files.
• Once created files may then be opened, read, rewritten. repositioned and closed, with all of which to corresponding system calls.
• Files have several attributes, including the file name, size, and the owner.
• System calls are also used to configure a files atributes.

Device Management

• Various systems have connected devices like printers, keyboards and hard disks.
• To request and to read / write a device, there system calls are required.
• To release the device after current operations, system calls are required.
• Lastly system calls to mount and unmount devices are required.

Information Maintenance

• Specific system calls exist to change or set the time and date.
• More calls set system data, processes, files or device attributes.

Communications System Calls

• System calls exist to create a connection and to delete the connection to remote machines.

Protection

• Calls are made to manipulate user permissions.
• This includes changing user/ group access, and changing the access permissions of files themselves.

System programs

• Provide a convenient environment for executing programs and dividing them, such as in a system call
• Manage files, status, and modifications; support programming languages;.
• Also support program loading, execution, and communication.
• System programs, not actual system calls largely define most user's experience
• The system gives a convenient environment for program development and execution.
• Some of these are simply user interfaces to system calls, while others are considerably more complex.

File Management System Programs

• Create/ delete files and manipulate their data.

Status Information

• Ask the system for info - date, time, amount of available memory, disk space, number of users
• These programs format and print the output to the terminal or other output devices.
• Some systems implement a registry used to store and retrieve configuration information

File modifications System Programs

• Text and special search commands to create and transform text files.
• Provide support for programming languages, compilers, and debuggers
• Load programs and debug at a high level of the machine code

Communications Support

• Allows access from other screens, provides web pages, send eletronic mail and transfer files.

Operating System Design and Implementation

• Design and Implementation of OS not "solvable", but approaches have proven successful
• Internal structure of different Operating Systems can vary widely
• Goals and specifications are defined and affected by hardware and system
• System goals focuses on if it is efficient, not error free, reliable and flexible.

Separation

• What will be done? That is the policy of the systems
• How do you preform the policy? That would be the mechanism
• Principle to what mechanisms do determine something and separate from flexible policy

Simple Structure

• DOS has the goal to has the most functions with minimal space usage.
• It's open so direct access device drivers.
• BIOS support applications to have a hardware independent output.

MS-DOS Layer Structure

• The simple structure DOS, was first founded august 12, not well organized
• No division on memory which ends up having program issues crash entire OS

Layered Approach

• Is based on multiple layer, that is easy to build on.
• The 0 layer is always hardware whilst N is user
• Layer are selected for how services are used.

UNIX System Structure

• Simple structure with lots of packing as a Monolithic, is too large
• Implementations require a too complex approach

UNIX

• Is limited to the hardware to have operating structure from two different parts
• Everything below is a system call, with hardware as a cpu or file

Microkernel System Structure

• Has "user" level spaces
• Communication is message passed
• More reliable and porteble plus extentable benefits a microkernel
• Though the performance may be lower to connect through the kernel

Modular System Structure

• Object Oriented approach as the kernel as most operating systems, is each loadable.
• Layers can be flexible.

Solaris OS

• The best OS for usage is on oriented objects for modular kernels
• On can be added at at start or runtime on runtime
• Has microkernel and other functions

Virtual Machine Cont

• Multiple processor to connect and communicate.

Virtual Machines

• Virtual Machine itself, and the kernel mode itself must be all on VM's own
• Having more user and kernal functions have have both modes run in the user modes

Virtual Machine Disadvantages

• Less efficient hardware access from it is running the host operating system to the machine and having to connect then to the kernel.
• It can be infected by process of the host of what's happening and cause the process isolation to have bugs.

VM advantages

• Can use different environments
• The ISA servers as Hardware
• Crash affects won't damage hardware.
• If there as virus it will only be temporary then will shut off the guest.
• Monitor security and quarantine issues during the analysis.

Why VMs?

• Its separates the system at single time but the system can be efficient of companys goals.
• VMs offer a solution to run separate operating systems on the same computer.

Hypervisor

• The hypervisor runs above the hardware the VM uses.
• Manage the system physical hardware and supports guest VMs.
• Bare metal, or a hosted type of OS.

Virtualization

• Untouched body of OS, hypervisor manages and processes with emulation
• Linux OS can runs on a Windows program

Para Virtualization

• Provides a guest with an identical system from it was from a system to hardware
• So when Solaris 10 operates can runs applications from other sources.

Type-1 Hypervisor

• In which this runs bare metal to the application it can run.

Virtual machine Architecture

• That has Linux for it's access to run on those machines

System Debugging

• It can generate error log flies or capture memory
• Optimizaion to tune has crash dumps
• Debugging is twice as hard , debug it to not do it again.
• With tools as DTrace can capture data to send out to those probes.

System Generation

• The systems is configures to compute by SYSGEN.
• The OS must have CPU amount and desired sizes
• System is to run on all class variety of machines with the proper variety with peripheral configurations

System Boot

• OS has made a new hardware as a hardware.
• Locates and restarts of kernel with small peices of code.
• Program the memory

Firmware vs OS

• Resides to operate on different levels.

Memory Intizalation

• CPU can be resetted to have Intilaziation with high speeds operating.

Main instructions

• To have a CPU and ROM with hardwire

Running steps

• Starts the shell and OS with certain commands like loading the Bootstrap.
• Runs and has its commands to restart again.

Boot Block

• It is a two step process is fixed and loads a loader start up firmware to execute