Introduction to os module 1 pdf operating system

FUNDAMENTALS OF OPERATING
SYSTEMS
S Savitha
Assistant Professor
ECE Dept

Module-1
Introduction: What operating systems do; Computer System Organization,
Computer System architecture; Operating System operations; Resource
Management
Operating System Structures: Operating System Services, User and Operating
System interface; System calls, Application Program Interface, Types of system
calls;

Operating system
An operating system acts as an intermediary between the user of a computer and
computer hardware. The purpose of an operating system is to provide an
environment in which a user can execute programs in a convenient and eﬃcient
manner
The most popular operating systems are Windows, MacOS, Android and Linux.

Purpose of Operating Systems
● Interface Between Hardware and Software
● File Management
● User Interface
● Ability to Run Programs
● Manage Hardware
Without an operating system, a computer would be like a collection of unconnected parts—its hardware
would exist, but there would be no way to control or interact with it in a meaningful way.

Deﬁnition
An operating system is a program that controls the execution of application
programs and acts as an interface between the user of a computer and the
computer hardware.
A more common deﬁnition is that the operating system is the one program
running at all times on the computer (usually called the kernel), with all else being
application program

How does an OS work?
● The OS is loaded into the computer by a boot program.
● Users interact with the OS through a user interface (UI), such as a
command-line interface (CLI) or a graphical user interface (GUI).
● Application programs use the OS by requesting services through an
application program interface (API).
● The OS manages the computer's hardware and software resources.
● The OS schedules tasks for eﬃcient use of the system.
● The OS keeps track of time and resources used by various tasks and users.

How does an OS work?
Once installed, an operating system relies on a large library of device drivers to
tailor its services to the speciﬁc hardware environment. For example, every
application could make a common call to a storage device. The OS receives that
call and uses the corresponding driver to translate the call into actions, or
commands, needed for the underlying hardware on that speciﬁc computer

Operating system as User Interface –
1. User
2. System and application programs
3. Operating system
4. Hardware

History of OS
1956 The ﬁrst Operating System was GN-NAA I/O in 1956 by Genera; Motors.
GM-NAA I/O (1956)
1960s IBM developed a time sharing system TSS/360 OS/360, DOS/360 and
TSS/360
1970s Unix popularized simplicity and multitasking; rise of personal computers
with basic OSs. Unix (1971), CP/M (1974)
1980s GUI-based OSs gained traction; networking features became standard.
Apple Macintosh (1984), Windows (1985)
1990s Open-source Linux emerged; GUIs in Windows and Mac OS improved.
Linux (1991), Windows 95 (1995)
2000s-Present Mobile OSs dominated; cloud and virtualization technologies
advanced computing. iOS (2007), Android (2008)

List of common Operating Systems
Windows OS
Developer : Microsoft
Key Features : User-friendly interface, software compatibility, hardware support, Strong gaming support.
Advantages : Easy to use for most users, Broad support from third-party applications ,
Frequent updates and support.
Typical Use Cases : Personal computing, Business environment, Gaming.
macOS
Developer : Apple.
Key Features : Sleek, intuitive user interface, Strong integration with other Apple products,
Robust security features, High performance and stability.
Advantages : Optimized for Apple hardware, Seamless experience across Apple ecosystem,
Superior graphics and multimedia capabilities.
Typical Use Cases : Creative industries (design, video editing, music production),
Personal computing, Professional environments.

List of common OS
Linux
Developer : Community-driven (various distributions).
Key Features : Open-source and highly customizable, Robust security and stability, Lightweight and can
run on older hardware, Large selection of distributions (e.g., Ubuntu, Fedora, Debian).
Advantages : Free to use and distribute, Strong community support, Suitable for servers and
development environments.
Typical Use Cases : Servers and data centers, Development and programming, Personal computing
for tech enthusiasts.
Unix
Developer: Originally AT&T Bell Labs, various commercial and open-source versions available
Key Features: Multiuser and multitasking capabilities, Strong security and stability, Powerful
command-line interface, Portability across different hardware platforms
Advantages: Reliable and robust performance, Suitable for high-performance
computing and servers, Extensive support for networking
Typical Use Cases: Servers and workstations, Development environments,
Research and academic settings

User View
● Ease of use
● Security

What does OS do?
System view:
● OS is a resource allocator ( manages all resources)
● OS is a control program (controls and executes program)

Functions of an Operating System
● Memory Management
● Processor Management
● Device Management
● File Management
● I/O Management
● Booting
● Security

User Interface or Command Interpreter

Performs Basic Computer Tasks
The management of various peripheral devices such as the mouse, keyboard, and
printer is carried out by the operating system. Today most operating systems are
plug-and-play. These operating systems automatically recognize and conﬁgure the
devices with no user interference.

Network Management
Network Communication: Think of them as traﬃc cops for your internet traﬃc.
Operating systems help computers talk to each other and the internet. They
manage how data is packaged and sent over the network, making sure it arrives
safely and in the right order.
Settings and Monitoring: Think of them as the settings and security guard for your
internet connection. They also let you set up your network connections, like
Wi-Fi or Ethernet

Computer Organisation
● Computer system
● Storage structure
● I/O structure

Interrupt timeline for a single program doing output

BOOTSTRAP
● The ﬁrst program to run on computer power-on is a bootstrap program, which
then loads the operating system
● Bootstrap is stored in (ROM)/ (EEPROM)

Interrupt
Interrupts are the events that take place to inform the operating system to stop the current execution of
the current process and handle the Interrupt Service Routine (ISR). ISR is responsible for finding out
which software or hardware caused the interruption and informing the CPU about it. CPU will service
the request and after the completion of the request, CPU resumes the execution of the process which
CPU was previously executing. Interrupts can be caused by hardware as well as software

Interrupt request lines.
nonmaskable interrupt, which is reserved for events such as unrecoverable
memory errors.
maskable: it can be turned off by the CPU before the execution of critical
instruction sequences that must not be interrupted. The maskable interrupt is
used by device controllers to request service.

The CPU hardware has a wire called the interrupt-request line that the CPU senses
after executing every instruction.

● The Von Neumann architecture, which is the foundation of most modern
computers. Named after John von Neumann.
● The Von Neumann architecture popularized the stored-program concept,
making computers more ﬂexible and easier to reprogram.
● This design stores both data and instructions in the same memory,
simplifying hardware design and enabling general-purpose computing.
● A single bus is used for transferring data, addresses, and control signals,
which can limit performance.
● Sequential Execution: Instructions are executed one at a time in a sequential
manner.
Von Neumann architecture

Von Neumann architecture
ﬁrst fetches an instruction from memory and stores that instruction in the
instruction register.
The instruction is then decoded and may cause operands to be fetched from
memory and stored in some internal register.
After the instruction on the operands has been executed, the result may be stored
back in memory. Notice that the memory unit sees only a stream of memory
addresses.

Storage Structure
Main memory ( RAM )
● Programs must be loaded into RAM to run.
● Instructions and data fetched from RAM into registers.
● RAM is volatile
● "Medium" size and speed
Volatile memory faster, smaller, and more expensive per bit:
● Registers
● CPU Cache
Non-volatile memory ( "permanent" storage ) is slower, larger, and less expensive per bit:
Electronic disks
Magnetic disks
Optical disks
Magnetic Tapes

1. Registers
Registers are small, high-speed memory units located in the CPU. They are used to
store the most frequently used data and instructions. Registers have the fastest
access time and the smallest storage capacity, typically ranging from 16 to 64
bits.
2. Cache Memory
Cache memory is designed to minimize the time it takes to access data by
providing the CPU with quick access to frequently used data.

3. Main Memory
Main memory, also known as RAM (Random Access Memory), is the primary
memory of a computer system. It has a larger storage capacity than cache
memory, but it is slower. Main memory is used to store data and instructions that
are currently in use by the CPU.
Types of Main Memory
Static RAM: Static RAM stores the binary information in ﬂip ﬂops and information
remains valid until power is supplied. Static RAM has a faster access time and is
used in implementing cache memory.
Dynamic RAM: It stores the binary information as a charge on the capacitor. It
requires refreshing circuitry to maintain the charge on the capacitors after a few
milliseconds. It contains more memory cells per unit area as compared to SRAM.

4. Secondary Storage
Secondary storage, such as hard disk drives (HDD) and solid-state drives
(SSD) , is a non-volatile memory unit that has a larger storage capacity than main
memory. It is used to store data and instructions that are not currently in use by
the CPU. Secondary storage has the slowest access time and is typically the least
expensive type of memory in the memory hierarchy.
5. Magnetic Disk
Magnetic Disks are simply circular plates that are fabricated with either a
metal or a plastic or a magnetized material. The Magnetic disks work at a high
speed inside the computer and these are frequently used.
6. Magnetic Tape
Magnetic Tape is simply a magnetic recording device that is covered with a
plastic ﬁlm. Magnetic Tape is generally used for the backup of data. In the case of
a magnetic tape, the access time for a computer is a little slower and therefore, it
requires some amount of time for accessing the strip.

Computer-System Architecture
● Single-Processor Systems
● Multiprocessor Systems
● Clustered Systems

Single-Processor Systems
One main CPU which manages the computer and runs user apps.
Other specialized processors ( disk controllers, GPUs, etc. ) do not run user apps.

Multiprocessor Systems
Increased throughput - Faster execution, but not 100% linear speedup.
Economy of scale - Peripherals, disks, memory, shared among processors.
Increased reliability
Failure of a CPU slows system, doesn't crash it.
Redundant processing provides system of checks and balances. ( e.g. NASA )

Clustered Systems
Independent systems, with shared common storage and connected by a
high-speed LAN, working together.
Special considerations for access to shared storage are required, ( Distributed
lock management ), as are collaboration protocols.

Operating-System Operations
● Multiprogramming and Multitasking
● Dual-Mode and Multimode Operation
● Timer

Types of OS
● Batch OS
● Multiprogramming OS
● Multitasking time sharing OS
● Multiprocessing OS
● Real time OS

Operating-System Structure
A time-sharing ( multi-user multi-tasking ) OS requires:
● Memory management
● Process management
● Job scheduling
● Resource allocation strategies
● Swap space / virtual memory in physical memory
● Interrupt handling
● File system management
● Protection and security
● Inter-process communications

Resource Management
Process Management
Memory Management
File-System Management
Mass Storage Management

Process Management
The OS has to create and delete processes, schedule processes (and threads) on
CPUs, suspend and resume processes, provide mechanisms for process
synchronization, and provide mechanisms for process communication.

Memory Management
The OS has to keep track of which parts of memory are currently being used, and
which processes are using them.
Allocate and deallocate memory space as needed.
Decide which processes (or parts of processes) and data to copy into or out of
memory.

File-System Management
The OS has to
● create and delete files
● create and delete directories (folders),
● support primitives for manipulating files and directories,
● map files onto mass storage, and back up files on stable (nonvolatile) storage
media.

Mass Storage Management
Regarding mass storage, the OS has to mount and unmount devices, manage free
space, allocate storage, schedule disk accesses, perform partitioning, and provide
protection.

Cache Management
Some of the caching that goes on in computers is controlled by the operating
system, and some is not.

Cache Management
Migration of integer A from disk to register

Security and Protection
● Modern computing systems require security and protection.
● The system grants only an authorized process access to a resource.
● The OS must surveil the system and ensure that resources are utilized safely
and correctly.
● To maintain protection and security, the operating system must manage
certain kinds of data, such as user ID numbers, group ID numbers, and
passwords.

Virtualization
● Virtualization is a technology that enables one computer to function
simultaneously as several different computers, each with its own operating
system.
● Under virtualization several guest operating systems can run 'on top of' a host
operating system, and all of these systems use the computer hardware
natively.
● A person might use a virtualized operating systems to run an applications
that is not available on the host operating system.
● If someone develops versions of a new application to execute on several
different operating systems, virtualization could allow the developer to test
and debug all the version on one computer.
● There is a Linux virtual machine provided with the text.

Timer
● Before the kernel begins executing user code, a timer is set to generate an
interrupt.
● The timer interrupt handler reverts control back to the kernel.
● This assures that no user process can take over the system.
● Timer control is a privileged instruction, ( requiring kernel mode )

● User Interfaces - Means by which users can issue commands to the system.
Depending on the system these may be a command-line interface ( e.g. sh,
csh, ksh, tcsh, etc. ), a GUI interface ( e.g. Windows, X-Windows, KDE, Gnome,
etc. ), or a batch command systems. The latter are generally older systems
using punch cards of job-control language, JCL, but may still be used today
for specialty systems designed for a single purpose.
● Program Execution - The OS must be able to load a program into RAM, run the
program, and terminate the program, either normally or abnormally.
● I/O Operations - The OS is responsible for transferring data to and from I/O
devices, including keyboards, terminals, printers, and storage devices.
● File-System Manipulation - In addition to raw data storage, the OS is also
responsible for maintaining directory and subdirectory structures, mapping
file names to specific blocks of data storage, and providing tools for
navigating and utilizing the file system.

● Communications - Inter-process communications, IPC, either between
processes running on the same processor, or between processes running on
separate processors or separate machines. May be implemented as either
shared memory or message passing, ( or some systems may offer both. )
● Error Detection - Both hardware and software errors must be detected and
handled appropriately, with a minimum of harmful repercussions. Some
systems may include complex error avoidance or recovery systems, including
backups, RAID drives, and other redundant systems. Debugging and
diagnostic tools aid users and administrators in tracing down the cause of
problems.

● Resource Allocation - E.g. CPU cycles, main memory, storage space, and
peripheral devices. Some resources are managed with generic systems and
others with very carefully designed and specially tuned systems, customized
for a particular resource and operating environment.
● Accounting - Keeping track of system activity and resource usage, either for
billing purposes or for statistical record keeping that can be used to optimize
future performance.
● Protection and Security - Preventing harm to the system and to resources,
either through wayward internal processes or malicious outsiders.
Authentication, ownership, and restricted access are obvious parts of this
system. Highly secure systems may log all process activity down to
excruciating detail, and security regulation dictate the storage of those
records on permanent non-erasable medium for extended times in secure
( off-site ) facilities.

System call
● The use of APIs instead of direct system calls provides for greater program
portability between different systems. The API then makes the appropriate
system calls through the system call interface, using a table lookup to access
speciﬁc numbered system calls
● Parameters are generally passed to system calls via registers, or less
commonly, by values pushed onto the stack. Large blocks of data are
generally accessed indirectly, through a memory address passed in a register
or on the stack

The handling of a user application invoking the open( )
system call

Introduction to os module 1 pdf operating system

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