Operating Systems: Intro and Functions

Introduction to Operating Systems

• An operating system (OS) is the primary software installed on a computer
• It manages all the hardware and other software
• The OS interfaces with computer hardware and provides services for application use
• A boot program initially loads the OS into the computer
• Application programs use the OS by requesting services through the Application Program Interface (API)
• Users interact with the OS via a Computer Command Line or Graphical User Interface (GUI)

Functions of Operating Systems

• Memory Management involves tracking primary memory, allocated memory addresses, and unused memory addresses
• Processor Management involves OS process scheduling, tracking processor status, allocating the processor (GPU) to a process, and de-allocating the processor when no longer needed
• Device Management includes managing device communication via drivers, tracking devices, deciding which process gets the device and for how long, efficiently allocating devices, and de-allocating devices
• File Management organizes file systems for easy navigation and usage, tracking information, location, uses, and status, and allocating/de-allocating resources
• Security protects computer data from illegal use, modification, or deletion, preventing unauthorized access via passwords and similar techniques
• Control Over System Performance involves recording delays between service requests and system responses
• Job Accounting keeps track of time and resources used by various jobs and users
• Error Detecting Aids assists in protection of dumps, traces, error messages, debugging, and error detection
• Coordination Between Other Software and Users involves coordination and assignment of compilers, interpreters, assemblers, and other software

Primary vs Secondary Memory

• Random Access Memory (RAM) is used for temporary storage and stores data in MBs
• RAM is volatile and used in normal operations, with faster writing speeds
• Read-Only Memory (ROM) is used for permanent storage and stores data in GBs
• ROM is non-volatile and used for startup processes, with slower writing speeds

Goals of Operating Systems

• The main goal is efficient use of memory, CPU, and Input Output devices
• A secondary goal is user convenience by providing user-friendly interfaces like GUIs to ease tasks and minimize interference

Two Majors Goals of Operating Systems

• Making the computer system convenient to use and utilizing computer hardware in an efficient manner
• Convenience is important in personal computers, and efficency is important when a computer is shared with multiple users

History of Operating Systems

• The history of operating systems is linked to the development of computer systems

Generation Zero

• English mathematician Charles Babbage designed the first true digital computer
• Babbage is knows as the Father of Digital Computer
• The computer had a mechanical design considered slow and unreliable and referred to as the "Analytical Engine"

First Generation (1940s-1950s)

• From 1945 to 1955, technology used vacuum tubes
• Operating systems were absent, and the language used was machine language (binary language)

Second Generation (1955-1965)

• From 1955 to 1965, the technology was transistors, and operating systems were present
• Languages used were assembly and high-level languages
• Transistors were introduced around 1955, and the first operating system was the Fortran Monitor System
• FORTRAN, a high-level language, was utilized

Second Generation Computers Features:

• Transistors were used as the main electronic component
• Computers were smaller, more reliable, and more powerful
• High-level languages such as COBOL and FORTAN were introduced
• Printers, tape storage, and memory began to be used, and processing speed improved to microseconds

Second Generation Computers Advantages:

• Able to compute scientific and engineering calculations
• Reduced computer costs and sizes
• Simplified programmer's job

Third Generation (1965-1980)

• Integrated circuits were single components containing multiple transistors
• Examples include PDP-8, PDP11, ICL 2900, IBM 360, and IBM 370
• Use of integrated circuits reduced computer size and computational time from microseconds to nanoseconds and improved the performance

Fourth Generation (1980-Present Day)

• Personal computers gained popularity
• IBM, creating a new PC, approached Bill Gates, and together they found DOS (Disk Operating System)
• The system was revised and renamed to MS-DOS, which topped the market
• Doug Engelbart of the Stanford Research Institute invented the GUI (Graphical User Interface), which uses icons, menus, and windows

Fourth Generation Notes:

• Steve Jobs, coinventor of Apple Macintosh, adapted GUI, leading to the success of Apple Macintosh
• Microsoft built a newer version of MS-DOS, becoming based on the success of Macintosh, and Windows was created

Batch Operating System

• Involves no immediate cooperation or interaction between the OS and the PC
• An operator sorts similar jobs with the same requirement into batches
• Examples include bank statements and payroll systems

Batch Operating System Advantages:

• Allows multiple users to share batch systems
• The idle time is minimal
• It is easy to manage large work repeatedly in batch systems

Batch Operating System Disadvantages:

• Difficult to estimate job completion time
• Operators must be knowledgeable about batch systems
• Debugging is hard, and it can be costly
• Other jobs wait an unknown time if any jobs fail

Time-Sharing Operating System

• Each task gets its opportunity to execute efficiently
• A "quantum" of time is allocated to each task
• Time Sharing OS is also known as Multitasking Systems

Time-Sharing Operating System Advantages:

• Each task gets an equal opportunity
• CPU idle time can be reduced
• There are fewer chances of software duplication

Time-Sharing Operating System Disadvantages:

• Reliability problems
• Security and integrity of user programs and data needed
• Data communication problem

Distributed Operating System

• Several independent yet interconnected computers communicate using a shared communication network
• These systems have their own memory unit and central processing unit (CPU)

Distributed Operating System Advantages:

• Failure of one system does not affect the network communication
• Electronic mail increases data exchange speed
• Shared resources make computation fast and durable
• Load on host computer reduces
• Systems are easily scalable
• Delay in data processing reduces

Distributed Operating System Disadvantages:

• Failure of the main network stops the entire communication
• Establishing distributed systems uses languages not well defined
• Complex underlying software makes these systems expensive

Network Operating System

• Involves a server on which systems run, providing the ability to manage users, data, and applications
• It facilitates sharing access to files, printers, and applications in a small private network where all users are aware of other users
• Systems in this OS are also called tightly coupled systems

Network Operating System Advantages

• Highly stable centralized servers
• Security concerns are handled through servers
• New technologies and hardware upgrades are easily integrated
• Server access is possible remotely from different locations and types of systems

Network Operating System Disadvantages:

• Costly servers
• User's dependence on a central location for most operations
• Regularly required maintenance and updates

Real-Time Operating System

• Used for real-time systems like Air Traffic Control Systems, Networked Multimedia Systems, and Command Control Systems
• This requires a very small time interval needed to process and respond to inputs
• This time interval is called response time

Real-Time Operating System Examples

• Examples include medical imaging systems, industrial control systems, robots, air traffic control systems, etc.

Real-Time Operating Systems: Hard vs Soft

• Hard Real-Time systems are used in applications with strict time constraints where even the shortest delay is unacceptable, built for saving life and used in automatic parachutes or air bags
• Virtual memory is almost never found in these systems
• Soft Real-Time OSs are used when the application's time constraints are less strict, but the system cannot frequently miss deadlines; Examples of soft real-time systems are personal computers, audio systems, and video systems

Hard Real-Time Characteristics:

• The Response time is hard-required
• Peak-load performance is predictable
• Control of pace is environment
• Safety is often critical
• Size of data files are small/medium
• Redundancy Type is active
• Data Integrity is short-term
• Error Detection is autonomous

Soft Real-Time Characteristics:

• The Response time is soft-required
• Peak-load performance is degraded
• Control of pace is computer
• Safety is non-critical
• Size of data files are large
• Redundancy Type is checkpoint-recovery
• Data Integrity is long-term
• Error Detection is user-assisted

Real-Time Operating System Advantages

• Maximum utilization of devices and resources for greater output
• Time assigned for shifting tasks is very less
• Time spent for shifting tasks in older systems is 10 micro seconds, but in latest systems is 3 micro seconds
• High focus on running applications with less focus on applications in queue
• Suited for embedded systems like transport since program sizes are small
• Error-free execution
• Memory allocation is well-managed

Real-Time Operating System Disadvantages:

• Limited Tasks: Very few tasks run at the same time
• Heavy use of system resources that might be expensive
• Complex algorithms
• Need for specific device drivers and interrupt signals to respond earliest to interrupts
• Poor thread priority management due to switching tasks more often

Handheld Operating System

• Designed to run on machines with lower speed processors and less memory
• Require fewer resources compared to other types of OS
• Palm OS, Pocket PC, Symbian OS, Linux and Windows are examples
• Handheld systems include Personal Digital Assistants (PDAs)
• Typical characteristics include limited size, limited memory, slow processors, and small display screens

Hand held Operating System Advantages

• Can be used on portable devices everywhere
• Cost-effective due to limited resource use
• It does not rely on non-portable power sources

Hand held Operating System Disadvantages

• Limited memory which requires efficient memory management
• Many handheld devices do not support virtual memory
• Faster processors not viable because they require more power and handheld devices have limited source of power

Components of Operating Systems

• System Component - A process, program, utility, or another section of a computer’s OS for managing different device areas; its not a hardware component either, but closely resembles a computer program

Shell Component

• Is a user interface for accessing an operating system's services
• Operating system shells use either a command-line interface (CLI) or graphical user interface (GUI)
• The name comes from being the outermost layer around the OS

GUI

• Interface using graphics to interact with the operating system using windows, scrollbars, buttons, wizards, painting pictures, alternative icons and many more
• Transmits information through the use of videos, images, and plain text

CLI

• Interface with permissions to write using commands or consoles to interact with the OS
• The command prompt is an example of this because user puts the writing command to tell the computer what to do

Memory Manager

• Focuses on allocating memory to different tasks, handling the Main Memory or RAM and tracks memory spaces needed by the running process
• Multitasking consumes memory space

RAM

• A high-speed storage for computers and their applications to utilize, store, and access temporary data
• Stores common data that programs use often, rather than storing the data on a slower medium like a Solid State Hard Drive (or SSD).

Memory Allocation

• Allocation happens after the portion of the memory is checked and deemed valid for the request, and de-allocation happens when it's time to reclaim that space
• The memory manager protects the main memory space from alterations

Process Manager

• Focuses on scheduling tasks and utilizing the processor
• It decides which process gets the processor
• Activities are information sharing and exchange of processes, protection of resources from one process to another and providing facilities for sharing and synchronization of processes

Security Manager

• Secures the whole computer against any unauthorized process or application

Second Storage Manager

• Used to store data that can be manipulated further in the system

Device Manager

• Controls devices such as the mouse, monitor, and other peripheral devices by instructing device drivers to write/store the file

File System Manager

• Offers addition, deletion, modification, and manipulation of user files
• File manager does naming and renaming files, copying files from one directory to another, and backup and recovery

Computer System

• Is composed of hardware, software, and liveware
• Hardware is the physical parts while software consists of programs/applications
• These three system components combine to process, receive, manipulate, display, and move data/information

Hardware System

• Includes physical parts such as the motherboard, input and output devices (like the keyboard and mouse), CPU, and storage devices

System Software

• Provides platforms to other software
• System servers, device drivers, and utility software are examples of low-level programs that run in the background while the OS is running

Application Software

• Performs a variety of specific tasks for the user
• Applications are already installed on the computer, or the user can install themself

Computer System Structure

• Main components consist of memory, CPU, disk controller, USB controller, and graphics adapter
• The USB controller then connects to the mouse, keyboard, and printer

Input Devices

• Used for entering data into the computer and includes microphone, keyboard, and scanner

Output Devices

• Puts out information or data to the user or to another device and includes headphones, speakers, and monitor

Processing Devices

• These are the core parts assigned to process data
• Examples of processing devices are the Central Processing Unit (CPU) and Graphics Processing Unit (GPU)

Storage Devices

• Stores the data on computer and has two subcategories
• Devices include Primary Storage, which is smaller in size and has the fastest data speed (Random Access Memory RAM) and Secondary Storage, which is bigger in size and has slow data speed (Hard Disk Drive, Optical Disk Drive, and USB Flash Disks/Drives)

Communication Devices

• Hardware devices assigned to transmit analog/digital signals/messages, either wirelessly or hardwired
• These devices include Bluetooth headphone, Modulator Demodulator or Modem, and Bluetooth Mouse

Central Processing Unit (CPU)

• Electronic circuitry within a computer that executes instructions that make up a program
• Performs arithmetic, logic, controlling, and input/output (I/O) operations specified by instructions in a program

Computer Boot-Up

• When computer starts, there is an operation peformed automatically by the computer called booting
• The system checks all the hardware and software and will load necessary files

Types of Booting: Warm vs. Cold

• Warm Booting is restarting a computer that is already powered on
• Cold Booting is turning on a computer after it has been powered off completely

Bootloader

• Also known as a boot program or bootstrap loader; special operating system software that loads into the working memory of a computer after start-up
• Generally launched by a bootable medium like a hard drive, CD/DVD, or a USB stick that receives information from the computer's firmware
• The whole process is also described as "booting"

Boot Sequence

• The order in which a computer searches nonvolatile data storage devices for program code to load the operating system (OS)
• Typically, a Basic Input/Output System (BIOS) is used to start the boot sequence and loads the operating system into system memory once the instructions are found

Normal PC Boot-Up Process

• The process before the boot sequence is the power-on self-test (POST), an initial diagnostic test when a computer is switched on
• If there are problems during POST, alerts are displayed
• If the boot device is not found, an error message is displayed, the system freezes or crashes

Traps and Interrupts

• Events that break the normal sequence of orders or instructions being processed or executed by the central processing unit (CPU)
• Traps, also known as faults or exceptions, are synchronous interrupts sensed by the CPU as an abnormal condition (meaning an error has happened)

Traps

• Switch the operating system to kernel mode, only returning to its originating process after it performs various actions
• Traps that take place in kernel mode are more fatal than user modes
• Errors can be in the form of invalid memory access, devision by zero, undefined code execution, non-existing peripheral devices access, breakpoint, and restriced memory location access

Device Drivers

• Software components augmented into an OS to handle a specific device.
• OS manages device drivers to handle all I/O devices
• They manages the data between the peripheral devices and alters its local buffer storage, then, transfers signals over cable or even in wireless

Device Driver Tasks

• Managing requests from the device independent software by accepting the appropriate tasks
• Executing required error handling and interact to give and take I/O with the device controller
• Ensuring all processes are completed and the request is executed successfully

I/O Operation

• Device driver starts by loading registers within the device controller
• The device controller examines the files and processes registers to determine tasks to execute
• Then, the controller begins to manage the transfer of data from the device to its local buffer
• After the transfer of data has been successfully completed, the signals are delivered by the local buffer interrupt

Methods in 1/0

• Synchronous I/O: CPU process waits while I/O proceeds
• Asynchronous I/O: I/O executes simultaneously with the processes of CPU

Polling

• Process of regularly checking the status of the device
• Involves actively examining the status of an external device by a client program, often utilized in terms of I/O and called polled I/O or software package-driven I/0
• Is the simplest method for an I/O device to interact with the processor

Storage Structure

• An essential component of a computer system because most processes are executed using memory
• Memory can be non-volatile or volatile

Volatile vs. Non Volatile Memory

• Non-volatile memory has the capability to hold saved data when the computer power is turned off and is used for consistent storage
• Volatile memory only manages and saves data while device is in use and is automatically removed when the device is turned off

Primary Storage

• Also as the main memory and stores program information
• Includes read-only memory (ROM) and random-access memory (RAM) and cache memory

Read Only Memory

• A primary, non-volatile altered or only can be stored when prompted
• Commonly used for programs or systems that frequently require a code to load it

Random Access Memory

• Also called as theread-write memory, it is primary storage
• The type of memory device because only is volatile and it does need an specific code to load.

Cache Memory:

• Used to store data and processes frequently required by the CPU
• Allows it to not have a code to search and manage memory, making this device efficient

Secondary Storage

• Has data stored, managed, data and information permanently
• This has these primary devices
• Hard drives
• Memory cards
• Flash drives
• CD ROM or compact disks

Hard Disk Drives

• Commonly usued
• Round pieces of metal with a magnetic disk

Memory Cards

• Card shapes and easily plugged

Flash Drives

• Easily called "Pen Drives
• Compact and has data in specific sizes

CD-ROMs / Compact Disks:

Usually store data and information on a silver device

Hardware Protection

• Refers to the identification of a system's physical components and their interrelationships, allowing designers to understand how different components fit into the system

Hardware Protection: Dual-Mode Operation

• Forms the basis of I/O, memory, and CPU protection
• There are two modes: Monitor mode (also called system or kernel mode) and user mode

Monitor Mode

• The CPU uses all instructions and access all areas of memory

User Mode

• CPU is restricted unprivileged instructions and a specified area of memory

Hardware Protection Categories

• CPU protection, memory protection, and is protected by making all input/output instructions privileged
• The associated timer device, the scheduler, timer interrupts,and CPU usage are protected by using timer devices
• Memory is protected into pieces
• I/O protection involves making all input/output instructions privileged, such that user code (running in user mode) must request I/O via system calls