OPSYS - OPERATING SYSTEM

What is Software?

• It is a programs used to direct the operation of a computer, as well as documentation giving instructions on how to use them. 
• It is a set of instructions or programs for controlling the computer.

Different Types of Software:

System Software
 It is a set of programs that controls the operations of the computer and its devices.

Application Software
It is a set of programs that performs specific tasks for users.

3 Types of Programs:

User/Application Programs

• Programs used by the users to perform a specific task.

System Programs

• An interface between user and computer.

Driver Programs

• Communicate with I/O devices with computer.

Architecture of Computer System

Computer system can be divided into four components:

1. Users
2. Application Program
3. Operating System
4. Hardware

What is an Operating System?

• It is a set of one or more programs which provides a set of services that interface applications to computer hardware and which allocates and manages resources shared among multiple processes.

2 Related Goals OF OS:

Convenience

• Operating System mainly developed to make the use of computer easier. 

Efficiency

• Operating System should ensure that the computer resources are managed properly. 

OS Functions and Purposes:

1. Resource Manager
2. Service Provider
3. Virtual Machine

Resource Manager

• Allocates scarce resources
• Protects entities from interfering with each other
• Protects itself and the overall system from both malicious and accidental damage
• Programs run at the pleasure of the OS

Service Provider

• Provides common functionality, simplifying applications
• Provides standard interfaces, making applications more consistent

Virtual Machine

• Defines a number of characteristics not found on the hardware
• Presents a cleaner and easier “machine” for applications to run on
• Hides the boundary between OS and hardware, allowing flexibility in hardware design while still running the same programs

Areas of Operating System Responsibility:

1. Processes Management
2. Memory Management
3. I/O Devices Management
4. File Systems Management
5. Security
6. Networking
7. User Interface

Process Management

• Manages CPU in terms of running programs, called processes
• Schedules processes, picking the next one to get the CPU
• Switches between processes, called context switching

Process Related Services

• Creating processes
• Terminating processes
• Changing process parameters (e.g. priority)?
• Providing inter process communication
• Providing process synchronization

Memory Management

• Assigns areas of memory belonging to processes to areas of physical memory
• Manages requests that exceed available physical memory
• Controls sharing of memory

Memory Related Services

• Direct allocation requests
• Direct freeing of memory
• Serving memory needs
• Managing sharing of areas of memory

I/O Device Management

• Provides common device interface tasks
• Manages exclusive access
• Hides device details

I/O Device Related Services

• Establish access to a device
• Release a device
• Read from a device
• Write to a device
• Grant exclusive access to a device
• Provide special device operations

File System Management

• Provides translation from names to resources
• Manages persistent storage of data
• Presents a device-independent interface
• Protects resources from unauthorized access

File System Related Services

• Open a file
• Close a file
• Read from a file
• Write to a file
• Seek within a file
• Query and modify file parameters

Security

• Part of other management responsibilities
• Authenticates the identity of a requester
• Authorizes access according to a security policy

Security Related Services

• Setting Security Policies
• Querying Security Polices
• Encrypting and Decrypting Message (especially carried over the network)

Networking

• Implements protocol stacks
• Provides services for:
• Establishing connections to remote systems
• Listening for connections from remote systems
• Exchanging data with remote systems

Networking Related Services

• Establishing a connection to a remote service
• Listening for connections from remote client
• Sending messages to a remote system
• Receiving messages from a remote system
• Closing a connection to a remote system

User Interfaces

• OS provides a design that have integrated the user interface which the user can deal with.

Techniques of Organizing Operating Systems:

• Different Operating System Structure:
• Monolithic Designs
• Layered Designs
• Microkernel Designs
• Virtual Machines Designs

Monolithic Designs

• Kernel structured as a single program
• Usual design techniques
• Often criticized

Layered Designs

• Dependency on only lower layers
• Tricky to structure
• Often requires splitting subsystems into multiple layers

Microkernels Design

• Move much of the traditional kernel functionality into separate programs
• Reduce the size of the kernel
• Components communicate with messages passed through the microkernel

Virtual Machine Designs

• Virtualize the hardware
• Create the illusion of multiple machines
• Each guest believes it has the hardware to itself
• Allows different OSs to run at the same time

History of the Operating System

• Pre-Batch Systems
• Simple Batch Systems
• Multi-Programmed Batch Systems
• Time-Sharing Systems
• Personal Computer Systems
• Parallel Systems
• Distributed Systems
• Real-Time Systems

Pre-Batch Systems

• No OS on earliest machines
• Collections of useful routines:
• First code reuse
• Foreshadowed the service provider aspect of operating systems
• Machines scheduled with sign-up sheets
• Issue:
• Too much spent time loading and reloading compilers.
• Solution:
• Batch all programs that use the same compiler.

Simple Batch Systems

• Development of high-speed magnetic tape.
• Bundles together all programs/jobs that use the same compiler.
• Issue:
• What if programs/jobs requires additional input?
• Solution:
• Spooling (Simultaneous Peripheral Operation On-Line)

Multi-Programmed Batch Systems

• Kept OS runs jobs one at a time based on a scheduling scheme.
• CPU is kept busy, less idle time waiting for I/O.
• OS rapidly switch among running programs.
• Issue:
• User cannot use the computer when he wants to.
• Solution:
• Allow multiple users to connect to the computer over modems from dumb terminals at home.

Time-Sharing Systems (Multitasking System)

• Multiple users all using a single computer at the same time.
• OS provides process synchronization and communication.
• OS provides deadlock avoidance.
• OS provides a file system.

Personal Computer Systems

• Computers finally become cheap enough for individual users to own.
• GOAL for OS is more of user convenience and efficiency.

Parallel Systems (Multiprocessor Systems)

• Computers having more than one processor.
• Also called as Tightly-Coupled system.
• 2 Techniques:
• Symmetric Multiprocessing
• Where each processors share the same memory and I/O; each processor works independently.
• Asymmetric Multiprocessing
• Where each processor is assigned a specific task; master-slave processors.
• Advantages:
• Increased throughput
• Economy Scale
• Increased Reliability

Distributed Systems

• After allowing multiple users and programs, multiple machines comes next
• Manage multiple computing systems as a single pool of computing resources
• Share file systems
• Support multiple CPUs cooperating on a single task
• Also called as Loosely-Coupled Systems
• Advantage:
• Resource Sharing
• Computation Speedup (Load-Sharing)
• Reliability
• Communication
• Scalability

Real-Time Systems

• OS must provides an output within a fixed timeframe.
• 2 Types:
• Hard Real-Time System
• System must perform in time or system will fail.
• Soft Real-Time System
• If system is unable to perform in time, performance degradation only.