Operating System: Hardware and User Interface

Operating System Basics

• The operating system is a manager of hardware and software.
• It acts as an intermediary between users and computer hardware.
• Primary objectives include controlling computer hardware and providing an interactive user interface for command interpretation.
• It is a fundamental component of nearly all computer systems.

Hardware Management

• The operating system manages and controls hardware resources like the processor, memory, and disk space.
• It displays outputs, including error notifications, on the monitor.
• The operating system error handling procedure ensures devices function and communicate properly.

User Interface

• The operating system organizes applications for user access, usage, and storage.
• It provides a stable and consistent way for applications to interact with hardware, abstracting hardware details from the user.
• It displays error messages when programs malfunction, regaining control and halting the application.

Computer System Components

• It comprises the computer hardware, operating system, utilities, application programs, and the end user.
• The operating system oversees and coordinates all hardware uses as well as various user application programs.
• It is the first program loaded and remains in memory continuously.

System Goals

• It aims to offer an environment for program execution that is characterized by its convenience to the user as primary goal.
• Efficiency in hardware utilization is a secondary goal.

User View

• User interaction with computer varies based on interface (Windows XP, Vista, 7).
• Personal computer OS design prioritizes ease of use and resource utilization.
• Mainframe/minicomputer setups involve shared resources accessed via terminals, with OS optimizing resource utilization.
• Workstations networked with servers and other workstations require the OS to balance individual usability and resource sharing.

System View

• From the computer's perspective, the OS mediates between hardware and software.
• It manages resources like CPU time, storage, and I/O devices.
• Being a control program concerned with operation usage and I/O, it manages user program execution and corrects errors.

Types of Operating Systems

• Early Mainframe Systems handled commercial and scientific tasks, evolving from batch processing to time-sharing systems.

Batch/Early Systems

• Early computers used card readers and tape drives for input, and line printers and card punches for output.
• Users submitted jobs including programming, data, and control information without direct computer interaction.
• The OS allowed automatic control transfer between jobs and resided in memory.
• Similar jobs are batched together to speed up processing. This was know as spooling.
• CPU downtime is the primary disadvantage.

Multiprogrammed Systems

• This uses CPU by organizing its jobs to always have one running.
• Keeping jobs in memory simultaneously to increase CPU usage.
• A subset of jobs is kept in the job pool.
• CPU can switch to another job if one job waits, improving efficiency.
• This system provides user decision making and multitasking also know as scheduling.

Time Sharing Systems

• Multitasking is achieved by rapidly switching between jobs for interaction.
• Interactive systems allow user communication with OS or programs via keyboard/mouse for quick responses.
• Short actions means less computing to each user, with the end resulting in multiple people working on the computer all at the same time.
• Memory management and protection and disc management are advantages of using this system.
• This also offers concurrent execution, and more complicated CPU schemes

Personal Computer System/Desktop System

• Personal computers in the 1970s prioritized user convenience and response.
• File protection is used when other computers have access to the PC.
• The lack of protection led to easy data destruction via self-replicating programs.

Microprocessor/Parallel/Tightly Coupled Systems

• These were equipped with multiple processors sharing bus, clock, memory, and peripherals. This is found in UNIX & LINUX.
• Multiprocessor systems improve throughout, reliability, and cost.
• Increased throughput
• Reliability if distributed among processors, the others do not need to halt when one does
• Multiprocessor systems lower cost, as they require less peripherals than a traditional setup

Symmetric Multiprocessing (SMP)

• Each processor has an identical copy of the OS and can communicate.
• Modern OS such as Windows NT, Solaris, LINUX, and OS/2 support SMP.

Asymmetric Multiprocessing (Master-Slave Processors)

• Each processor tackles explicit tasks, with the master processor allocating and scheduling work for the slaves used by Sun's SUNOS version 4.

Distributed Systems/Loosely Coupled Systems

• Processors have memory not shared to other clocks. Communication between these systems is done over phone lines. Function by networking, this system can share computational task with many users through a network.

Real Time Systems

• Used when there is strict time requirements on operations.
• With processors sensing data, the computers analyze the data and change controls over the system. A proper real time system will only return when there are correct results within the time constraints.
• Data is stored in short term memory or read only memory.
• These two types of Real Time Systems work such as:
• Hard real time systems: guarantees critical task execution on time, meaning abrupt tasks are also quick.
• Soft real time systems: critical tasks have priorities if the system can work. Meaning occasional deadlines are acceptable. For multimedia.

Basic Functions of Operating Systems

• Some various functions for operating systems consists of the following such as:

Process Management

• A processes execute a computer with instructions used by the CPU. Time shared user programs are processes.
• Sends output to the printer for processes. Which uses the CPU time, files & Input/Output devices. All are provided through the OS when its creates & runs certain processes.

Main Memory and Memory Management

• A main memory is very important to the modern computer. All data in these systems stores quickly using the CPU & Input/Output device, The main memory instructs to central locations to read & write memory instructions, which help CPU process data for disc.

File Management

• One of the most import computer OS, is the ability to hold large amounts of data to read later.
• With multiple media types such as magnetic tape, or optical disk, the OS can store a lot of files with lots of data.
• This can also creates directories

Input and Output System Management

• This hides peculiarities for the hardware from a user.
• Sub systems within the OS hide the details to the user for convenience, and makes it easy to work with.

Secondary Storage Management

• The main purpose to execute programs which exist in main memory while running.
• Small amount of computer power is lost during this activity.
• Also responsible for following actions with file management:
• Free Space Management
• Storage allocation
• Disk Scheduling

Networking

• Through communications media through a high speed buses or networks. This way they can communicate.
• The communication networks has also had considerations, message routing and connecting with security.

Protection or Security

• Multi users means concurrent execution where processes can be protected through memory usage.
• Mechanisms makes files, memory segments, CPU's and other resources being used only as ones are authorized.

Command Interpretation

• With communication it acts as a interface

System Calls

• Interface with instructions for writing for a assembly language. Making them in a higher language.

Process Control

• These instructions help create, abort, kill, and use processes along with managing and having the ability to edit these abilities when needed for specific instructions.

File Manipulation

• Create files / delete files and work with data that is being stored. Read, edit text and rewrite.

Device Management

• Request specific devices for different areas, and read write, as well as reposition

Information Maintenance

• Set data and find out what is set to be used.

Communication

• Communication with interfaces between the process & the OS. Which are available in the form of assembly language.

Simple Structure

• These commercial systems doesn't have a well defined structure, which leads to operating systems that begins with small and then grows as the system grows.

Layered Approach

• Broken OS is broken in to parts, or levels that is put on top of layers. The bottom layer is hardware / top layer is the interface.

System Programs

• In the area of system programs, here are some that are important to take a look at:
• Programming loading
• Communications

Process management

• A process is a program in execution that does instructions in a sequential order. A process includes things such as method addresses, data location, and value of the registers. Also that makes the process.
• Programs and processing are not always the processes. Programs being passive but the process is active with actions to the directory for executions.

The processes use a scheduling algorithm to determinate when to work and what task the system should complete. The system varies with states such as:

• New: Creating
• Ready: Needs to assign processor
• Running: Executing
• Waiting: Event/instructions
• Terminated; Complete

There are many state at ready / waiting but, there are only one state at instant.

Process Queues

• Process then enter system it gets put into the job queue with are made of process.
• Process that are ready & waiting gets put into read queue

Types of Queues:

• Ready queue: a ready queue header contains pointers to the first PCB in the list, but each PCB has a pointer field that tells the nest PCB in ready queue.
• Each list of the given process waits on a list referred to as a device queue.
• The new process goes to ready queue awaiting execution of the CPU

Types of scheduling

• Operating System choose processes from queues in a certain way which causes it to be in a system that will execute that will run at a faster speed through processes

• scheduler : the parts that picks the job / processor

• these are also are assigned to a a particular scheduler

These Types :

• Long term scheduler: process done on the main drive or disk, is loaded up into memory for the purpose of multi programing. (executes less frequently then others processes) the long term scheduler is called from the program leaves the system. The processes here either Input, or Output which is also know are I/O bond or CPU bond. • I/O Bond : An program or that has a lot of tasks that do not run as often. • CPU bond : A process or program that spends more time creating computations then other I/O process. • Short- term scheduler : ready for executing ,allocates CPU to the process. The differences makes the frequency of the execution. The short term makes processes of tasks in CPU fast. ( one in hundreds of milliseconds ) • Medium term scheduler some running systems introduce another layer of scheduling for the media, where that tasks are to remove processes to then reduce its work in to memory. The processing will reintroduced so it can preform it previous processes (referred to as swapping)

Process control block

• Referred as OS process control block to process control, or another task is known as a task control block.

Which contains the following

• Process state: The state may be new, ready, running, waiting or terminated state.
• Program counter:it indicates the address of the next instruction to be executed for this purpose.
• CPU registers: The registers vary in number & type depending on the computer architecture. It includes accumulators, index registers, stack pointer & general purpose registers, plus any condition- code information must be saved when an interrupt occurs to allow the process to be continued correctly after- ward.
• CPU scheduling information:This information includes process priority pointers to scheduling queues & any other scheduling parameters. Memory management information: This information may include such information as the value of the bar & limit registers, the page tables or the segment tables, depending upon the memory system used by the operating system. Accounting information: This information includes the amount of CPU and real time used, time limits, account number, job or process numbers and so on.
• I/O Status Information: This information includes the list of I/O devices allocated to this process, a list of open files and so on. The PCB simply serves as the repository for any information that may vary from process to process

CPU Algorithms and Scheduling

• CPU Scheduling deals with the problem of deciding which of the processes in the ready queue is to be allocated first to the CPU. There are four types of CPU scheduling that exist.

First Come, First Served Scheduling (FCFS) Algorithm

This is the simplest CPU scheduling algorithm. In this scheme, the process which requests the CPU first, that is allocated to the CPU first. The implementation of the FCFS algorithm is easily managed with a FIFO queue. When a process enters the ready queue its PCB is linked onto the rear of the queue.

Shortest Job First Scheduling (SJF) Algorithm

This algorithm associates with each process if the CPU is available. This scheduling is also known as shortest next CPU burst, because the scheduling is done by examining the length of the next CPU burst of the process rather than its total length.

Priority Scheduling Algorithm

• In this scheduling a priority is associated with each process and the CPU is allocated to the process with the highest priority. Equal priority processes are scheduled in FCFS manner.

Round Robin Scheduling Algorithm

• This type of algorithm is designed only for the time sharing system. It is similar to FCFS scheduling with preemption condition to switch between processes. A small unit of time called quantum time or time slice is used to switch between the processes. The average waiting time under the round robin policy is quiet long.

Process Synchronization

• A co-operation process is one that can affect or be affected by other processes executing in the system. Co-operating process may either directly share a logical address space or be allotted to the shared data only through files. This concurrent access is known as Process synchronization.

Critical Section Problem

• Consider a system consisting of n processes (P0, P1, .........P -1) each process has a segment of code which is known as critical section in which the process may be changing common variable, updating a table, writing a file and so on. The important feature of the system is that when the process is executing in its critical section no other process is to be allowed to execute in its critical section. The execution of critical sections by the processes is a mutually exclusive. The critical section problem is to design a protocol that the process can use to cooperate. Each process must request permission to enter its critical section. The section of code implementing this request is the entry section. The critical section is followed on exit section. The remaining code is the remainder section.

Semaphores

• Synchronization for problems. It must have three following conditions that consists of

Mutual Exclusion

• Process is executing critical selection, when other processes happens.

Progress

If no process is executing critical set / some the processes enter it should no enter into remainder.

Bounded Waiting

Number of the other processes will enters to make a change, but there could be one bound after request.

Techniques

Important sections

• The operating system will then have the ability to make some instructions and edit different areas such as data and code.
• This way there will be different things that can be done between the functions for its use for its application
• Each type can be assigned to be one part in an area that helps the users through all the applications needed.

Virtual Machines

These are computer machines that can execute certain types of programs at the same time. This means there is multiple steps need to get to specific code.

• They need help using the CPU

I/O Structure

Consists of a CPU with multiple different drivers, which requires specific devices..

I/O Interrupt

• It start a Input or Output by loading its register with a device, it then determines the process its taking.
• For an controller reading data it take the info into the driver, and controller interrupts the CPU with a given amount of actions to take
• These action are started using Synchronous and asynchronous

DMA CONTROLLER

• HIGH I/O devices in DMA, the device enters a block of data to and from buffer. From buffer it gets stored memory to the OS.
• Operating system searches in buffer and finds driver registers to appropriate and sets its use for start and destination addresses & then transfer length which, when it’s then instructed to start I/O Operation.
• But cycle can be high when transferring large files.

This then can be slow due to stealing memory cycles from the CPU

Storage Structure

The Storage has these two memories:

• Main Memory
• Secondary Memory The data resides in memory while its used or in process, but they sometimes cannot be stored permanently

Main Memory

• Stores all storage area for CPU's usage of data and help with using the instructions. Must be resided in the correct and direct access or that can be ran on the CPU