Sistemas Operativos

Chapter 1: Introduction

What is an Operating System? Mainframe Systems Desktop Systems Multiprocessor Systems Distributed Systems Clustered System Real -Time Systems Handheld Systems Computing Environments

What is an Operating System?

A program that acts as an intermediary between a user of a computer and the computer hardware. Operating system goals:
Execute user programs and makesolving user problems easier. Make the computer system convenient to use.

Use the computer hardware in an efficient manner.

Computer System Components

1. Hardware – provides basic computing resources (CPU, memory, I/O devices). 2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users. 3. Applications programs –define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs). 4. Users (people, machines, other computers).

Computer System Organization
Computer-system operation
One or more CPUs, device controllers connect through common bus providing access to shared memory Concurrent execution of CPUs anddevices competing for memory cycles

Abstract View of System Components

Operating System Definitions
Resource allocator – manages and allocates resources. Control program – controls the execution of user programs and operations of I/O devices . Kernel – the one program running at all times (all else being application programs).
Kernel Services: Process Management Memory Management Filesystems Device drivers System calls Interprocess communication Network protocols

Simple Batch Systems
A fairly simple operating system was used. An operator other than user was needed. A card reader was used as input device. CPU is generally idle due to low speeds of mechanical I/O devices compared to those of electronic ones (e.g. slow punch card reader). Processing speed is increased by batchingsimilar jobs together and run them as a group. Automatic job sequencing allows transfer of control from one job to another.

Spooling
Jobs are not read directly into memory but onto the disk. Since reading is time consuming, some other jobs can be performed during reading. Overlap I/O of one job with computation of another job. While executing one job, the OS:
Reads next job from card readerinto a storage area on the disk (job queue). Outputs printout of previous job from disk to printer

The main goal is reduce CPU idle time

Multiprogrammed Batch Systems
Several jobs are kept in main memory at the same time which is known as job pool. The operating system picks one job from memory to execute. When a job has to wait, operating system switches to another job. Eventually, thefirst job finishes waiting and gets the CPU back.

OS Features Needed for Multiprogramming

Memory management – the system must allocate the memory to several jobs. CPU scheduling – the system must choose among several jobs ready to run. The system must know their exact locations in memory Management of devices including allocation.

Time-Sharing Systems–Interactive Computing

Atime-shared OS uses CPU scheduling and multiprogramming that provides each user a small portion of time. The CPU is multiplexed among several jobs that are kept in memory and on disk (the CPU is allocated to a job only if the job is in memory). The CPU is switched among multiple processes so frequently that the users may interact with each program during execution. A job swapped in and out of memory to thedisk. On-line communication between the user and the system is provided Time-sharing also compensates for low-speed I/O operations such as low-speed keyboard typing .

Desktop Systems
Personal computers – computer system dedicated to a single user. I/O devices – keyboards, mice, display screens, small printers. User convenience and responsiveness. Can adopt technology developed for larger...