Operating Systems: Tasks and Goals

Data Processing and Operating Systems

• An operating system (OS) manages the interaction between hardware and software components of a computer, making it user-friendly.
• The OS hides the complexity of hardware access by sending commands to controllers, which handle tasks like accessing hard drive caches and calculating data block positions.
• The OS acts as an interface between the user and the computer hardware components.

Tasks of an Operating System

• Operating systems manages system resources such as CPU, memory, and printers.
• The OS allows multiple users to print simultaneously, ensuring documents are separate and not mixed up.
• Resources are managed based on time (CPU allocation) and space (memory, storage).

Goals in Developing Operating Systems

• Extensibility: The OS should facilitate easy implementation of new features and requirements.
• Portability: Code should be platform-independent and not limited to machine language.
• Reliability & Robustness: The OS should ensure fault tolerance, protect users and processes from each other, and define reactions to errors.
• Compatibility: The OS should support standardized interfaces, including those from previous versions.
• Interface: Interfaces provide a transition point between software systems, enabling data exchange and processing.
• Performance: Efficient use of resources and quick response times in processing.

Client-Server Architecture

• In client-server setups, only process management and inter-process communication (IPC) run in kernel mode.
• Remaining processes are offloaded to user mode, in isolated and multiple process execution.
• Services are provided over the network for other computers.
• The set up enables concurrency, redundancy and distributed computing.
• A drawback is an overhead in the message system, including transfer data, compute times and more resources.

Operating System Concepts

• System calls that the OS offers to users or programmers for system operations
• Operation of system through command line or GUI (Graphical User Interface)
• OS manages and organizes task completion for processing requests,.
• Intercation between different applications using processes and data exchange.
• OS stores data over session runs and realizes files and databases to performs actions like opening, closing, reading, writing, etc.

Structuring Operating Systems

• The OS kernel directly manages hardware, defining process and data organization.
• Requirements for OS development can be realized through various structures and types of construction.

Monolithic Operating Systems

• The processor runs in two modes: kernel (privileged) mode for the OS and user mode for applications.
• The OS consists of procedures and functions, with frequent intercalling.
• These systems can be hard to modify and update.

Layered Operating Systems

• Layered OS architecture create virtual machines, where each layer offers more service to the underlying layer.
• Every layer has specific tasks, and the CPU runs in user or kernel mode

Client-Server Model

• Clients request a service via a message and receive a response back.
• In the user mode can only use a light Microkernel.
• Services handled in the usermode, small kernel remains.

Hybrid Systems

• Combined approach using Layered and Client-Server Models
• Windows uses this as the core of its structure since Windows NT

Processes vs Threads

• Processes enable multiprogramming stack operation, timesharing, and real-time functionality.
• All multitasking operating systems depend on process management as foundation

What is a Process?

• A program that's running
• One instance of a software application running on a computer
• The key unit allocated a processor to run on.
• The unit of activity distinguished by a single sequential execution thread, current state, and set of system resources.

Components of a Process

• Executes program (i.e., in the main memory)
• The correlating data of a program (e.g., the variables, operating landscape)
• Execution Setting, the program's status, it needs to perform.

Operating System and User Processes:

• Distinct kernel controls all operating system functions
• Operations outside the kernel are called user processes

Kernel Mode vs User Mode

• Kernel Mode: Privileged CPU state for OS with higher privileges.
• User Mode: Least CPU privilege level for general applications.
• Biggest part of the OS is done in User mode which means the OS must run in kernel or user mode.

Process States

• A process alternates states from the available to running
• Managed by state model for actions being used.

Simplified State Model

• Blocked: waiting for process to run or complete
• Ready: not selected for executing
• Active: active process while CPU is in operation
• Terminated: End operation

Process Management

• Keeps all record of the processes in Process Listing & Control Block

Components of Process Control Block Information

• The state of that Process
• Program Counter
• Pointers that allocate memory.
• Where files are saved.
• Timing.

Basic of Process Model

• The combining + control of OS
• Managing process execution, also its states and how it unfolds
• Managing all of the OS, controlling its CPU and OS settings.

Process vs Thread

• Process executes a software program
• Has secured entry upon files, other processes, or files.
• Each process has its own isolated memory
• Each consist of a thread

Thread (light weight process)

• Reserving a position for Thread OS, a connection for Threads
• Controlling OS in place - each with access
• Can get input + data from processes as long as memory is avalible
• OS within a process can go parallel
• can OS multithread

Pros and Cons of Threads within OS

• Thread easier to create, less demand
• Thread terminate must be a reason
• Memory, does not need allocation but is needed, however context need to be allocated

Examples of threads

• Working on multiple threads
• Taking in user input - other user formatting the text

User Thread Types

• Application control the thread within OS
• All app must multithread
• Thread book must the thread and order

Cons of Threads

• System must be in thread, all process must have those.
• Cannot have better processing.

Kernel Threads (where thread is controlled)

• Kernel takes care of what thread is managed
• All apps use thread API of kernel
• Operating and running these things.

Cons:

• Sending process means sending kernel
• Takes time for transfer

Thread run times

• User: very quick
• Kernel: longer than user
• Process much longer than kernel

SMP Multiprocessor Systems

• Like operating system minimum requirements being added- better multitasking
• Several Threads within only some CPUs
• Several CPUs can run kernal all together, but must be able to stay consistent
• More speed can only be maintained in parts

Benefit and Disadvantage of Threads:

• Can be parallel and has boosted OS
• More complexity between each
• More complicated for code and finding bugs

Process Control for Linux

• Process is rep by data Structure which is task struct.
• Has info on what's executing for the time.

Concurrency Issues

• OS must be to track available processes.
• Must designate time for OS also give it out.
• All data must be unreadable
• All results must remain consistent.

OS and Concurrency Taskload

• Must allow all actions even when another app is running
• Making what resources have been already locked down for process
• Can still be done with the processes

Avoidance:

• OS can set for resource, but can 2 processes get the same at the same time?
• Will result in not being able to access.

Semaphore and Mutual Exclusion

• Used often for OS + Programming.
• Will cause process to wait, signal when ready to continue

Semaphores

• Integers with 3 processes to control
• S is known as initial semaphore
• Waits for less to begin
• Enters programming through its operations

Implementing Semaphores

• Semaphore must use waiting list to be accessed
• Can be FIFO strict, or flexible.

Semaphores examples

• Process that takes input + output.
• Proccess D starts.

Locks Semaphores

Each of these control process within memory locations

Semaphores + Moniters

• Has many operation types and can coordinate tasks
• has wait and signal
• easier to coordinate between others.
• can be used with whatever is being requested

What is a monitor?

Used for both processes for each data type

Aspects of Moniters

• Can happen under 3 different factors
• All others are secured
• Can work as both OS and OS software

Concurrency within Monitors

Control of concurrency must be locked down.

Communication in multi processing tasks:

• OS with task - both must achieve what is needed
• synchronization to keep out other concurrent or process

Requirements for Communication

• Needed sync for mutual exclusion
• Has access within kernel, must be kept safe at all times

Approaches to the above

• Sendor with data ready
• Sender and data all ready
• Sendor sends msg while unlocked data will have many problems during time

Organization Types

• All items must be in logical order
• Very important to ensure a strong file structure

Characteristics

• Data type of drive
• Application
• Complexity
• Presentation
• Mistimes etc

General data

Can have various options

• Ansomming
• Sequence
• Index
• hashed

Ansoming Data

• To only collect and store, non need more
• Have both short + long fields

Sequential

• Record and fixed.
• Have both types.
• Should only search and not get every data

Multi processing

• Disk
• Caching of memory.

Allocating within the file

• Disk
• No location as is.

Data Allocation

• Os in charge - assign what needs what
• Tasks: -- Place Memory, Allotment -- Space of how big will be required

Data structure of what required

• OS must what's alloted
• Max memory

File allocation-

• Can have the sections in them
• Table showing each

Fragmenting the Space

• Group the first one known

Indexed

• Show whats required in the OS
• Can do quick scan.
• OS in charge of memory - but must have the block

Memory allocation -

Not only allocated Can have diff parts Lock it to avoid issues Easier to have the OS Should have data lock

Files in hardrives

Need different types of types Smaller has quick acess Big only be accessed

OS and it

Os must find if memory location is avail