3. Operating Systems - Informática Ingeniería en Electrónica y

Definition
Processes
File System
User Interface
3. Operating Systems
Informática
Ingenierı́a en Electrónica y Automática Industrial
Raúl Durán Dı́az Juan Ignacio Pérez Sanz
Álvaro Perales Eceiza
Departamento de Automática
Escuela Politécnica Superior
Course 2014–2015
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Definition
Processes
File System
User Interface
Contents
1
Definition
2
Processes
3
File System
4
User Interface
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Definition
Processes
File System
User Interface
Objectives
Basic Definitions
Objetives
Understand what an Operating System -OS- is and its utility.
Describe its different functional parts and their roles.
Understand what a process is.
Understand what a file system is.
Learn to use the basic Linux commands, the standard
Input/Output, and how to concatenate different commands.
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Objectives
Basic Definitions
What is an Operating System?
Definition
An Operating System -OS- is a program that manages the
hardware resources of a computer providing services for other
programs and applications. It works as an intermediate between
the user and the computer hardware, facilitating its use making it
more efficient.
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Definition
Processes
File System
User Interface
Objectives
Basic Definitions
OS functions
The main OS functions are:
To facilitate the use of the computer and, in general, the
communication computer-user
To manage and assign hardware resources (processor, memory,
peripherals) to processes, and deal with conflicts.
To manage and maintain files in permanent memory devices
(hard drive..)
To protect data and programs (specially important in
multiuser systems)
To serve different users.
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Objectives
Basic Definitions
Extended Machine
The OS construct another level of abstraction presenting the user
a virtual or extended machine with a much simpler use.
It hides fine working details the user does not need to know
(e.g. how to manage the read/write head of a magnetic disc)
It provides an extra set of instructions, the System Calls
They can be used by other programs or by the programmer
working as an interphase with the OS
They perform useful tasks, such as
Manage processes (create, cancel,...)
Manage files (create, open, close)
Manage memory (load, move or free blocks of memory)
The OS converts system calls in machine instructions (the only
ones that the computer executes); they are as well virtual
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Definition
Processes
File System
User Interface
Objectives
Basic Definitions
Extended Machine
nivel máquina simbólica
Compiladores
Editores
Intérprete de comandos
nivel máquina extendida
Sistema Operativo
nivel máquina real
Instrucciones en lenguaje máquina
Figure: Different levels of abstraction -machines- in a computer
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Objectives
Basic Definitions
Resources Administrator
It assigns hardware resources (processor, cores, memory) to
each process or user
Resolve conflicts among users
Example
If various programs/users want to print at the same time, OS
assigns priority and arrange them sequentially.
Example
While a process is waiting from data coming from hard disc, the
OS can allow another process to use the processor
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Definition
Processes
File System
User Interface
Definitions
Structure
Process management
Processes
Definition
A process is a program in execution. It is the main executive
element in the computer
We can see a process as the dynamic instance of a program.
Therefore it may happen that various processes execute the
same program (e.g. with different input).
A computing system working is a set of one of more processes
in execution according to a temporal planing established by
the OS or the programmer.
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Definitions
Structure
Process management
Elements of a process
A process can be described as:
Memory space structured in sections
Processor registers.
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Definition
Processes
File System
User Interface
Definitions
Structure
Process management
Process structure
$SP
Pila
Direcciones de memoria crecientes
Un proceso necesita manejar registros de la CPU:
11111111111111111
00000000000000000
00000000000000000
11111111111111111
00000000000000000
11111111111111111
00000000000000000
11111111111111111
Hueco libre (variable)
$GP
Datos dinámicos
Datos estáticos
•contador de programa $PC
•puntero de pila $SP
•registro de estado $PSW
Instrucciones
$PC
Reservado
0
Figure: Structure of a process allocated in memory
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Definitions
Structure
Process management
Process Features
A process can just be created by another process.
Any process (parent) can create other processes (child).
Two system calls are used to create new processes:
fork: system call by which a process creates a copy of itself;
exec: Replace the contents of a running process with another
program code.
The general way of launching a new program is first to fork an
existing process to create a new one, and then exec the new
program in it (i.e. load it in memory and execute it)
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Definition
Processes
File System
User Interface
Definitions
Structure
Process management
Process Tree
A
B
C
D
E
F
Figure: Process Tree
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Definitions
Structure
Process management
System (Boot)
When turning on the computer
The program counter PC points to an address at ROM where
there is a small code (BIOS -Basic Input/Output Services- in
IMB PCs) that becomes the first process to be executed. This
process initializes and tests the system hardware components
and starts a bigger process, the
Boot Loader that loads first the OS kernel and subsequently
the rest of the OS necessary to start main computer functions.
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Definition
Processes
File System
User Interface
Definitions
Structure
Process management
Executable File Structure
Secciones
Símbolos
Datos estáticos
Instrucciones
Cabeceras
Figure: Executable File Structure
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Definitions
Structure
Process management
Process Scheduling
The processor is the most valuable resource in the computer.
It can just execute one process every time.
When a process in execution is blocked (e.g is waiting for data
coming from disc), the Scheduler suspends it and selects
another process that can be executed, so to maximize the
processor use.
Each process is described by the memory space it uses and by
the content of the registers in the moment it is suspended.
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Definition
Processes
File System
User Interface
Definitions
Structure
Process management
Scheduling: monoprogramming
Recursos
impresora
dispositivos E/S
disco
puerto USB
proceso 1
sistema operativo
11
00
00
11
00
11
00
11
00
11
011
1
00
0
1
00
011
1
00
11
fin proc. 1
11111
00000
00000
11111
0
1
00
11
0
1
00
11
0
1
00
11
1111
0000
0000
1111
00
11
0
1
00
11
0
1
00
11
0
1
CPU no usada
CPU
inicio proc. 1
CPU no usada
proceso 2
inicio proc. 2
Tiempo
Figure: Scheduling with monoprogramming
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Definitions
Structure
Process management
Scheduling: multiprogramming
Recursos
E/S proc. 1
E/S proc. 1
impresora
dispositivos E/S
disco
puerto USB
proceso 2
CPU
proceso 1
sistema operativo
inicio proc. 2
proc. 2 interrumpido
por el s.o.
continúa proc. 2
11111
00000
0000
1111
00
11
00000
11111
0000
1111
00
11
fin proc. 1
00000
11111
0000
1111
00
11
00000
11111
0000
1111
00
11
00000
11111
0000
1111
00
11
0
1
00
11
00
11
0
1
0
1
00
0
1
00
11
00
11
0
1
011
1
00
11
inicio proc. 1
Tiempo
Figure: Scheduling with multiprogramming
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Definition
Processes
File System
User Interface
Definitions
Structure
Process management
Scheduling: Round-robin
Usually there are many processes waiting to be executed, so
the scheduler must apply some rule to distribute the processor
time.
The Round-robin scheduling consists of assigning time
intervals T or quantums to each process and to rotate among
them
The critical decision is T: short quantums implies to loose too
much time in process change; and long ones may imply too
much waiting for users.
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Definitions
Structure
Process management
Scheduling: Process state diagram
fin, error
Nonato
Finalizado
cancelado, error
distribuidor
distribuidor
Listo
fin E/S
cancelado, error
distribuidor
Activo
E/S
Bloqueado
Figure: Process state diagram (New, Ready, Running, Blocked,
Terminated)
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Definition
Processes
File System
User Interface
Definitions
Structure
Process management
Virtual Memory
Basically it consists of using secondary memory (hard disc) as
if it was principal memory (RAM)
The OS offers a process the possibility of using much more
memory, the virtual memory than the real one, the physical
memory
This allows the system to execute much bigger programs, and
more processes at the same time
The OS construct a page table for each process to traduce
virtual addresses to physical ones
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Definitions
Unix/Linux File System
File System
Definition
It is the part of the OS that controls how data is stored and
retrieved.
It consists of dividing information in pieces, the files, giving
them names and positions in memory, so that the information
is easily identified and accessed.
Example
There are different files systems. Each OS can manage different
ones. Most common actually are: FAT32 (Windows, Linux), ext4
(Linux), NTFS (Windows), HFS+ (Mac OS X), ISO9660 (for optical
discs).
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Definition
Processes
File System
User Interface
Definitions
Unix/Linux File System
System calls to manage files
The main system calls to manage files are:
create/open
read/write
close
unlink: To delete files (removes the file name from the file
system)
Note
They are OS-dependent (i.e. different for different OS), but
file-system independent.
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Definitions
Unix/Linux File System
Directory Tree
raíz
clases
informática
física
trabajos
ficheros
pelis
ice-age
shrek
Figure: Example of a directory Tree in Unix/Linux
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Definition
Processes
File System
User Interface
Definitions
Unix/Linux File System
Devices and files in Unix/Linux
Unix/Linux manages devices (e.g. hard disc or pen-drive) as
files.
They are usually placed in the /dev directory .
System calls are the same than for the ordinary files.
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Definitions
Unix/Linux File System
Mount point
When installing a new device, the file system uses a Mount
Point that it is just a directory in the system where the new
devices is mounted.
The user sees that the directories and files in the device
appear in a previously empty directory of the file system.
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Definition
Processes
File System
User Interface
Concept
Shell Interface
User Interface
The User Interfaces is a part of the OS that allows interaction
with the user through peripherals (keyboard, screen...)
The most common UI are:
Command Line Interface: Orders are typed with the keyboard
in a terminal, the OS interpret those commands looking for the
programs to execute and directing results to output devices.
Graphical user interfaces (GUI) (e.g Windows). Mouse and
keyboard are use to select icons in the screen and the output is
graphical output on the computer monitor.
Touchscreens. Input touching a screen (tablets, mobiles...)
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Concept
Shell Interface
Shell Program
It is a very complete Interface program that works as a
command-line interface. The user types commands and the Shell
execute them. Some of its features are:
Standard Input/Output;
Command concatenation,
pipeline;
Environment variable (PATH, HOME...)
Some basic commands:
ls -l, cd, pwd, mkdir, rmdir, ps...
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