3. Operating Systems

3. Operating Systems Informática Ingeniería en Electrónica y Automática Industrial Raúl Durán Díaz Juan Ignacio Pérez Sanz Álvaro Perales Eceiza Departamento de Automática Escuela Politécnica Superior Course 24 25 Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 1 / 28 Contents 1 2 3 4 Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 2 / 28

Objetives Objectives Basic s 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. Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 3 / 28 What is an Operating System? Objectives Basic s 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. Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 4 / 28

OS functions Objectives Basic s 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. Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 5 / 28 Extended Machine Objectives Basic s 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 Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 6 / 28

Extended Machine Objectives Basic s 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 Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 7 / 28 Resources Administrator Objectives Basic s Example It assigns hardware resources (processor, cores, memory) to each process or user Resolve conflicts among users 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 Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 8 / 28

s 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. Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 9 / 28 Elements of a process s A process can be described as: Memory space structured in sections Processor registers. Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 10 / 28

Process structure s $SP $GP $PC Pila Un proceso necesita manejar registros de la CPU: 00000000000000000 11111111111111111 00000000000000000 11111111111111111 Hueco libre (variable) 00000000000000000 11111111111111111 00000000000000000 11111111111111111 Datos dinámicos Datos estáticos Instrucciones Reservado 0Direcciones de memoria crecientes contador de programa $PC puntero de pila $SP registro de estado $PSW Figure: of a process allocated in memory Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 11 / 28 Process Features s 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) Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 12 / 28

Process Tree s A B C D E F Figure: Process Tree Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 13 / 28 System (Boot) s 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. Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 14 / 28

Executable File s Símbolos Secciones Datos estáticos Instrucciones Cabeceras Figure: Executable File Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 15 / 28 Process Scheduling s 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. Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 16 / 28

Scheduling: monoprogramming s Recursos impresora dispositivos E/S disco puerto USB proceso 2 inicio proc. 1 fin proc. 1 inicio proc. 2 CPU proceso 1 sistema operativo 00000 11111 00000 11111 CPU no usada 01 01 CPU no usada Tiempo Figure: Scheduling with monoprogramming Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 17 / 28 Scheduling: multiprogramming s Recursos impresora E/S proc. 1 E/S proc. 1 dispositivos E/S disco CPU puerto USB proceso 2 proceso 1 inicio proc. 1 0011 0011 0011 inicio proc. 2 continúa proc. 2 proc. 2 interrumpido por el s.o. 0011 0011 01 01 01 01 01 fin proc. 1 sistema operativo Tiempo Figure: Scheduling with multiprogramming Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 18 / 28

Scheduling: Round-robin s 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. Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 19 / 28 Scheduling: Process state diagram s fin, error Nonato distribuidor cancelado, error Finalizado distribuidor Listo fin E/S cancelado, error Activo distribuidor E/S Bloqueado Figure: Process state diagram (New, Ready, Running, Blocked, Terminated) Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 20 / 28

Virtual Memory s 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 Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 21 / 28 s Unix/Linux It is the part of the OS that controls how data is stored and retrieved. Example 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. 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). Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 22 / 28

System calls to manage files s Unix/Linux Note 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) They are OS-dependent (i.e. different for different OS), but file-system independent. Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 23 / 28 Directory Tree s Unix/Linux raíz clases trabajos pelis ficheros informática física ice-age shrek Figure: Example of a directory Tree in Unix/Linux Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 24 / 28

Devices and files in Unix/Linux s 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. Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 25 / 28 Mount point s Unix/Linux 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. Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 26 / 28

Concept Shell Interface The s 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...) Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 27 / 28 Shell Program Concept Shell Interface 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... Raúl Durán Díaz, Juan Ignacio Pérez Sanz, Álvaro 3. Operating Perales Eceiza Systems 28 / 28