Operating System - Operating Systems - Lecture Slides, Slides of Computer Science

Download Operating System - Operating Systems - Lecture Slides and more Slides Computer Science in PDF only on Docsity! Operating Systems Lecture 03: Operating System Overview 1 Docsity.com Today • Announcements: – Proposal: change in TAs schedule – Piazza – Slides posted before class on course page: • Operating Systems Overview: – Definitions (as many variants as textbooks…) – Historical perspective • Solution today’s “jeopardy” – Grade yourself and hand it to me 2 Docsity.com The Operating System as a User/Computer Interface This image cannot currently be displayed. 5 Docsity.com Key Interfaces • Instruction set architecture (ISA) • Application binary interface (ABI) • Application programming interface (API) 6 Docsity.com The Operating System as a Service Provider • Program development (not really part of OS) • Program execution • Access I/O devices • Controlled access to files • System access • Error detection and response • Accounting 7 Docsity.com Evolution of Operating Systems  A major OS will evolve over time for a number of reasons: Hardware upgrades New types of hardware New services Fixes 10 Docsity.com In the Beginning…  In the beginning: Expensive Hardware, Cheap People.  Goal: maximize hardware utilization.  (Now: Cheap Hardware, Expensive People.)  Goal: make it easy for people to use computer. 1940s to mid 1950s:  computers were huge machines, expensive to buy, run and maintain  used in single user, interactive mode  programmers interact with the machine at a very low  no OS. 11 Docsity.com The Birth of the OS (1) • Problem: Need code to manipulate external I/O devices: – Complex – Appears in all programs – Always written from scratch – Includes: • loading the compiler and the code into memory; • saving the compiled program (executable); etc., • which meant mounting/dismounting tapes or setting up card decks. • Solution: Build a subroutine library (device drivers) to manage the interaction with the I/O devices. – library loaded into the top of memory and stays there. – the first example of something that would grow into an operating system. 12 Docsity.com Processor Point of View • Processor executes instruction from the memory containing the monitor • Executes the instructions in the user program until it encounters an ending or error condition • “control is passed to a job” means processor is fetching and executing instructions in a user program • “control is returned to the monitor” means that the processor is fetching and executing instructions from the monitor program 15 Docsity.com Job Control Language (JCL) Special type of programming language used to provide instructions to the monitor what compiler to use what data to use 16 Docsity.com Desirable Hardware Features • while the user program is executing, it must not alter the memory area containing the monitor Memory protection for monitor • prevents a job from monopolizing the system Timer • can only be executed by the monitor Privileged instructions • gives OS more flexibility in controlling user programs Interrupts 17 Docsity.com The Growth of the OS (3) • Problem: at any given time, the job is either using the OS or I/O (resource underutilization) • Problem: one job cannot keep both CPU and I/O busy • Solution: allow the job to overlap I/O and computation – Buffering and interrupt handling added to the subroutine library • Solution: multiprogramming 20 Docsity.com Multiprogramming • With uniprogramming: there must be enough memory to hold the OS (resident monitor) and one user program • With multiprogramming: OS and 2 programs in memory! – When one job needs to wait for I/O, the processor can switch to the other job, which is likely not waiting for I/O 21 Docsity.com Multiprogramming Example Table 2.1 Sample Program Execution Attributes JOBI JOB2 JOB3 Type of job Duration Memory required Need disk? Need terminal? Need printer? if Docsity.com Time-Sharing Systems • Can be used to handle multiple interactive jobs • Processor time is shared among multiple users • Multiple users simultaneously access the system through terminals, with the OS interleaving the execution of each user program in a short burst or quantum of computation 25 Docsity.com Evolution of Operating Systems: Overview  Stages include: Serial Processing Simple Batch Systems Multiprogrammed Batch Systems Time Sharing Systems 26 Docsity.com