Introduction to Operating Systems

• Education is not the learning of facts, but the training of the mind to think, Albert Einstein
• Introduction To Operating Systems

Outline

• Definition of Operating System (OS)
• History of OS's
• Computer Hardware Architecture
• Types of Operating System
• Operating System Concept
• System Calls
• Hypervisor

Learning Outcomes

• Know the definition, importance, and main jobs of an Operating System
• Differentiate between two modes of operation: Kernel and User
• Know the main points in the history of Operating Systems
• Review the computer hardware architecture.
• Differentiate between different types of Operating Systems
• Know the main concepts and components of an Operating System.
• Define a System Call
• Know the importance of a System Call
• Differentiate between the different types of System Call, the usage, and the functions of each type
• Understand the Concept of Virtualization

Definition of OS

• Computers use a layer of software, the Operating System, to provide User programs with a better simpler computer model and handle resource management

Where the OS fits in?

• User interface like shell or GUI is the lowest level of user-mode software
• It enables users to start programs like Web browsers, email readers, or music players
• The OS runs on bare hardware and provides the base for all software
• It interfaces between software and hardware
• Software is on top of the hardware
• Most computers have two modes of operation, kernel mode, and user mode
• Hardware is at the bottom with chips, boards, disks, keyboards, monitors, and physical objects

Kernel Mode vs User Mode

• The OS runs in kernel mode (or supervisor mode) which is fundamental software
• Kernel mode grants complete hardware access allowing execution of any instruction
• Other software operates in user mode, limited to a subset of machine instructions

What is an OS?

• A major task is hiding hardware and present programs with nice abstractions
• Operating Systems convert the complex to the beautiful, masking underlying details

OS Layers of Abstraction

• OS provides layers of abstraction to simplify complex hardware interactions
• An OS deals with hardware, and offers an interface to read and write disk blocks
• Programs can create, write, and read files without dealing with messy hardware details

What is an OS?

• An OS delivers an order and controlled allocation of the processors, memories, and I/O devices

What is an OS?

• Buffers output destined for a printer on disk
• Modern OS allows multiple programs in memory at the same time

Two Main Jobs of OS

• Providing abstractions to application programs
• Managing pieces of a complex system
• The abstraction that the kernel provides for application developers is called the system call API
• System Call API allows software developers to easily build applications to run on different types of hardware

The First Generation (1945-55): Vacuum Tubes

• Computers relied on machine language, which is the lowest-level programming language computers understand
• Computers could solve one problem at a time

Second Generation (1955-65): Transistors and Batch Systems

• High-level programming languages were being developed; examples include COBOL and FORTRAN
• Store computer instructions in memory, moved from magnetic drum to core technology

The Third Generation (1965–1980): Integrated Circuits

• Transistors were miniaturized and placed on silicon chips, called semiconductors
• Integrated circuits increased reliability, speed, and efficiency with low energy consumption
• Users interacted with third generation computers through keyboards, monitors, and interfaced with an Operating System
• Operating Systems allowed run many different applications at one time with a central memory monitoring program
• Computers became accessible to a mass audience smaller and more affordable

Third Generation

• SPOOL (Simultaneous Peripheral Operation On Line) is a kind of buffering mechanism
• Data is temporarily stored to be used and executed by a device, program or system
• Data is sent and stored in memory until the program or computer requests it for execution

Fourth Generation (1980–Present): Personal Computers

• Thousands of transistors/integrated circuits were built onto a single silicon chip.
• Windows Timeline, Macintosh Timeline, and Unix History
• Achieved through LSI (Large Scale Integration)

Fifth Generation (1990–Present): Mobile Computers

• Evolution of Mobile Phone
• Most Dominant Mobile Operating Systems -IOS released by Apple in 2007 -Android released by Google in 2008

Components of a Simple Personal Computer

• Components include Monitor, Keyboard, USB printer, and Hard disk drive
• CPU/MMU and memory
• Video, Keyboard, and USB controller
• Hard disk controller
• All communicate via a Bus

CPU: Central Processing Unit

• Fetch Stage: The next instruction is fetched from memory
• Decode Stage: the encoded instruction is interpreted by the decoder
• Execute Stage: The control unit of the CPU passes the decoded information, actions are performed, and the result is stored

CPU Architecture

• PC (Program Counter): Memory Address of the next instruction to be fetched
• CIR (Current Instruction Register)
• AC (Accumulator): Intermediate ALU results are stored

Memory

• Memory is ordered by speed
• Fastest to slowest: Registers, Cache, Main Memory, Magnetic Disk
• Typical Access Times: nanoseconds, milliseconds
• Typical capacity: KB, MB, GB, TB

Computer Hardware Architecture

• Input and Output Devices (I/O)
• The operating system only deals with the Controller

Computer Hardware Architecture

• First Method is User Mode, Second Method the Interrupt controller, and Third Method DMA Controller

Computer Hardware Architecture

• Programmed I/O, I/O occurs under the direction and continuous control

Computer Hardware Architecture

• Interrupt-driven I/O, an I/O command is issued and interrupted
• I/O hardware signals for end of I/O operations

Computer Hardware Architecture

• Direct Memory Access (DMA), a specialized I/O processor takes control of an I/O operation to move a large block of data

Buses

• Buses are used to link components or devices to a computer
• Address Bus is used by a microprocessor to identify memory storage location
• Data Bus is used to transfer data from one place to another in the computer system
• Control Bus transmits command signals bidirectionally from the CPU

Basic Input Output System BIOS

• BIOS is the program of a computer's microprocessor uses to start the computer system after it is powered on
• Manages data flow to the hard disk, video adapter, keyboard, mouse, and printer

Types of Operating System

• Mainframe Operating Systems are used for business transactions and can handle many jobs simultaneously
  • Handle batch jobs and transaction processing with timesharing capabilities
• Server Operating Systems run machines that have dedicated servers
  • Examples are Solaris, Linux, and Windows
  • Allow resource sharing and store webpages

Types of Operating System

• Multiprocessor Operating Systems: Also known as parallel computers or multicomputer
  • They have strong connectivity and high speed communication mechanisms and function as multiple processors into single system
• Embedded Operating Systems, these operating systems are preinstalled on devices and cannot be changed by users
  • Examples include washing machines and ovens

Types of Operating System

• Personal Operating Systems are common and designed for a single machine
  • Word, Excel, Browsers
  • Examples are Linux, Windows, and Mac
• Sensor Node Operating Systems are used to protect buildings and guard national borders
  • Able to detect forest fires, measure temperatures, and forecast weather to glean enemy movement information

Types of Operating System

• Real Time Operating Systems: These operating systems are divided into hard and soft real time
  • Hard: stringent time constraints, certain actions should occur only at that time, components coupled tightly
  • Soft: can miss deadlines with no permanent consequences
• Smart Card Operating Systems: Runs smart cards, has CPU imbedded

Operating system Concept

• A process is a 'program in execution', and has files registers, and code
• Address Space or Virtual Address Space (VAS)

Terminology

• PID is a number used by operating system to uniquely identify an active process
• UID (User Identification) assigned by the Administrator whose child parent process the same UID
• GID is the number assigned to a group

Address Space / Virtual Address Space (VAS)

• Virtual address range starts at a low address and goes up to the highest address
• VAS can be 4 bytes for 32-bit systems, 8 bytes for 64-bit systems

Address Space / Virtual Address Space (VAS)

• Each user gets a unique address space, OS maintains distinction between addresses
• The User can start multiple tasks through TCBs (Task Control Blocks) which allows programs to run
• Thread Control Block (TCB) is a data structure storing needed to manage a thread

Address Space

• Stack contains data such as such as return addresses, procedure arguments, temporarily saved registers, and variables
• Heap stores dynamically allocated variables
• BSS stores data representation at the machine level and allocates space for data
• Data contains the statically allocated variables
• Text contains machine code for the professor

Virtual Memory Management

• Mechanism used to manage memory using hardware and software
• Virtual memory is a part of secondary storage that acts as part of the main memory
• Aids in running multiple apps/increases programming
• Implemented with demand paging

Virtual Memory Management

• Virtual memory behaves as if its total RAM resources were equal to the whole amount of physical RAM and virtual RAM
• Mitigates system overload and allows for less physical RAM

Files

• The file system hides the messiness of storage types, e.g disk, CD, cloud drives, etc., details from the application programs

Operating System Concept

• Data and Address
• Operating systems provide services like device drivers to manage these components
• All protected with security by the protection systems

Operating System Concept

• UNIX sets owner, group, and other read/write/execute bits on every file.
  • For example: rwxr-xr--

Operating System Concept

• UNIX Shells use command line interfaces
  • The Bourne shell uses the $ as a prompt while the C Shell uses the %.

System Call

• A program running in User Mode calls the OS and asks for a resource access as kernel mode
• System Call Sequence for writing a simple program to read data from one file and copy them to another file
  • Writing a prompt, Accept Input, Writing a Prompt, Accept Input, Open Input File, Create Output File
  • Loop: Write to Output File, Read from Input File, Close Output File
  • Writing Completion Message and Terminate Completely

System Call Type

• Process Control
• File Manipulation
• Device Manipulation
• Information Maintenance
• Communications

Hypervisor

• A hypervisor, also known as Virtual Machines Monitor (VMM), creates and runs Virtual Machines (VMs)
  • Allows one host computer to support multiple guest VMs by sharing its resources (memory, processing)

Benefits of Hypervisor

• Speed, Efficiency, Flexibility
• Hypervisors can separate the OS from underlying hardware, so the software no longer relies on specific hardware devices or drivers

Hypervisor Types

• Two types of Hypervisors: type 1 and type 2

Type 1 Hypervisor

• Acts like a lightweight OS and runs directly on host's hardware
• Replaces the hosts OS and lies right on top of the hardware
• VMware hypervisors like vSphere, ESXi and ESX, Microsoft Hyper-V, Oracle VM Server, Citrix Hypervisor

Type 2 Hypervisor

• Hosted, running as software on the OS (like computer programs), which in turn runs on the physical hardware
• Used to run multiple Oss on one personal computer, such as either Windows or Linux
• VMware Fusion, and Oracle VirtualBox include Oracle VM Server for x86