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Pitt CS 1550 - Introduction to OS

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Intro to OS Pitt MosséIntroduction to OS (cs1550)• Why take this class? Why with Mosse?– it’s mandatory – it’s a great class– it’s a great prof– it’s easy (NOT!!!! do not fool thyself!)– it’s good for you• Life is not life anymore while this class is going on. Be careful! Specially if you’re taking also compilers or some other hard programming class…Intro to OS Pitt MosséClass Outline• Book: Tanenbaum’s Modern OSs• Intro to OSs (including Real-Time OSs)• Processes (definition, synchronization, management)• Memory (virtual memory, memory allocation)• IO (disks, sensors, actuators, keyboards, etc)• InterProcess Communication (networking, data transmission, etc)• Fault Tolerance, Real-Time and Security (time permitting)Intro to OS Pitt MosséSchedule and Grading• Pop quizzes 10% of grade: about every 2.5 weeks• Programming assignment (NACHOS on UNIX) 30% of grade• Midterm 30% of grade: around March 1• Second Exam 30% of grade : April 19• Class participation may carry 5% of grade for extra credit• Project 0 is self-test!!! For you to test whether you will die or not taking this class… Add/drop period ends Tuesday Jan 17thIntro to OS Pitt MosséOperating Systems• Manages different resources (CPU, mem, disk, etc)• Improves performance (response time, throughput, etc)• Allows portability, enables easier programming (no need to know what the underlying hardware)• Interface between the hardware and the rest of the machine… editors, compilers, user programs, etc• Standard interface is typically done in two ways:– system calls: control goes to the Operating System– library calls: control remains with the UserIntro to OS Pitt MosséBrief History• First Generation of computers had no OS: single-user. All coding done directly in machine language, memory resident code (no other resources to manage)• Second Generation has basic OS: batch processing. Read input (tape/cards), process, output to tape or print• Third Generation improved life: multiprogramming!Careful partitioning of memory space (4-12KB), drums and disks added for reading cards and spooling outputs (Simultaneous Peripherals Operations On-Line)• Time-sharing created several virtual machinesIntro to OS Pitt MosséHistory (cont)• Fourth Generation: PCs and workstations. Cheaper, faster, more user-friendly (Thank Macs for interfaces!)• UNIX precursor MULTICS (MULTIplexed Information and Computing Services) was the first “modern” OS. Bell+MIT+GE (MULTICS --> units --> Unix)• Berkeley improved on it: paging, virtual memory, file systems, signals (interrupts), networking!Intro to OS Pitt MosséNetworking!• Networked OSs are connected through a network, but user needs to know the name/type/location of everything• Distributed OSs (e.g., Amoeba, Mach, Locus) provide transparency to user, yielding one huge virtual machine!• Specialized OSs are built for specific purposes: routing engines (Networking), lisp machines (AI), time constrained applications (Real-Time), Internet (WWW servers), massively parallel uses (supercomputers), etc• All these are coming together, hard to identify boundaries anymore.Intro to OS Pitt MosséMicrosoft World• Excellent marketing, some good products• OSs started with DOS (Disk OS), no nothing, just very simple commands!• Windows 3.1 was a huge jump (based on decades-old technology initially developed at Xerox then Macs)• Windows 95 (released in 96) improved tremendously the state-of-the-affairs for MS, but still unreliable• Windows NT approaches Unix distributions, with more user-friendly interface.Intro to OS Pitt MosséUnix World• Created at AT&T, re-written/improved by Berkeley• ATT had majority control and good support (reliable OS)• OSF (Open SW Foundation, now Open Group) is a consortium of several companies to standardize UNIX• Different subgroups (syscalls, shells, RT, etc)• Standardization is with respect to interfaces and not implementation of primitives. Impln is left to the implr• Modern applications are time constrained (tel, video, etc)• Real-Time playing an increasingly important roleIntro to OS Pitt MosséOS Structure• Interface can be done atany level (depends onlevel of security of OS)• Interface with the lowerlevel layer gets translated• Machine dependent language used for accessing hardware• Main advantage of direct resource access is efficiency• Main advantage of indirect access is portability• Completely layered OS? Why or why not?USEROSHardwareDev DriversIntro to OS Pitt MosséOS Functions• Controls and manages resources (disks, memory, CPU, …); sends/receives control commands and data• Allows multiprogramming (several programs “at the same time” in the same resource)• Carries out communication between processes (inter and intra processor)• Manages interrupt handlers for HW and SW interrupts• Provides protection and security to processes• Prioritizes requests and manages multiple resources in a single machine (eg multiprocessors or CPU IO reqs)Intro to OS Pitt MosséOS Functions• OS manages resources, including management of– processes (creation, deletion, suspension, comm, synch)– main memory (usage, alloc/de-alloc, which processes get it)– 2ary storage (disk scheduling, alloc/de-alloc, swapping, files)– IO interfaces and devices (eg, keyboard, caching, memory)– protection (authorization, file and memory protection, etc)– InterProcess Communication (intra- and inter-machines)– Command interpretation (shells to Xlate user to OS). Typically includes the user interface that the OS uses.Intro to OS Pitt MosséOS Structure• Hardware at the bottom layer• Accessing the lower layer thruthe higher layers• DOS programs can access HW• Unix has controllers and devdrivers (DD) controlling devices• system calls are the interfacebetween user and OS (DDs)• libraries and system programsinvoke sys_callsUSEROSHardwareDev DriversTypical DOSTypical UnixUSERKernel FunctionsHardwareDev DriversSystem ProgramsIntro to OS Pitt MosséOS Structure• Interface can be done at any level (depends on security)• Machine dependent language used for accessing HW• Main advantage of direct resource access is efficiency (less


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