Introduction. Organizzazione del corso: Materiale Didattico Libro di testo: Organizzazione del corso: Materiale Didattico.

Transcription

1 Introduction Organizzazione del corso: Materiale Didattico Libro di testo: OperatingSystems GaryNutt Addison-Wesley(pearson) terza edizione Non esiste traduzione E consigliato seguire perchè l organizzazione degli argomenti non segue nessun testo in particolare Organizzazione del corso: Materiale Didattico Altro materiale: Lucidi delle lezioni (deliberatamente in inglese!) Codice sorgente, esempi... Sul sito docente: cliccare su Courses

2 Organizzazione del corso: Modalità d esame L esame si consegue superando Due prove in itinere (scritte) durante il corso oppure Una prova scritta (all incirca la somma delle due prove in itinere) al termine del corso, oppure negli appelli ordinari Le 2 prove in itinere non sono recuperabili non sono conservative Non è previsto esame orale Organizzazione del corso: Contatti Giuseppe Boccignone Dipartimento di Scienze dell'informazione Via Comelico 39/41 room: P106 (primo piano) tel (office):! !boccignone@dsi.unimi.it URL:! Organizzazione del corso: ultima info Perspectives of the Computer Questo è l ultimo lucido in italiano... Buon lavoro! Is this the only perspective on computing?

3 Perspectives of the Computer Perspectives of the Computer Human-Computer Interface API OS Interface Application Software System Software (More Abstract Resources) Trusted OS (Abstract Resources) Software-Hardware Interface Hardware Resources maybe not... Perspectives of the Computer Perspectives of the Computer: a vision of the future

4 Perspectives of the Computer Computing today The future: computation will be humancentered. Freely available everywhere, like oxygen in the air we breathe. We will not need to carry our own devices around with us. Configurable generic devices (handheld or embedded) will bring computation to us, whenever we need it and wherever we might be. We'll communicate naturally, using speech and gestures that describe our intent The guiding principle Entia non sunt multiplicanda praeter necessitatem (William of Ockham s razor) Systems that focus on a single task need not have an OS that was designed to handle 100 timesharing users! What is OS for? An OS is the part of the software that interacts directly with the computer hardware to export an abstraction of the hardware behavior using an application programming interface (API). A simple OS is designed to create simple (abstract) interfaces to the computer s hardware components A complex OS may define a correspondingly more complex virtual machine (s).

5 The Beautification Principle The Resource Principle An OS is a set of algorithms that hide the details of the hardware and provide a more pleasant environment An OS is a set of algorithms that allocate resources to Abstract Units of Computations (AUC) The OS abstract machine Example: Disk Abstractions OS Programmer Application Programmer load( ); seek( ); out( ); void write() { load( ); seek( ) out( ) } int fprintf( ) {... write( ) } (a) Direct Control (b) write() abstraction (c) fprintf() abstraction

6 Computing today : Small Computers PDAs, STBs, embedded systems became commercially significant Have an OS, but Not general purpose Limited hardware resources Different kinds of devices Touch screen, no keyboard Graffiti Evolving & leading to new class of Oses PalmOS, Pocket PC (WinCE), VxWorks, Computing today : Process Control & Real-Time Computer is dedicated to a single purpose Classic embedded system Must respond to external stimuli in fixed time Continuous media popularizing real-time techniques An area of growing interest Process Control & Real-Time ReadyWhenUR: Kettle that can be textmessaged to boil water Embedded system example: Digital Camera switch on

7 Embedded system example: ASIMO Embedded system example: ASIMO Computing today: Personal Computers CPU sharing among one person s processes Power of computing for personal tasks Graphics Multimedia Trend toward very small OS OS focus on resource abstraction Rapidly evolved to personal multitasking systems Computing today : Timesharing Systems Result Command Result Command Result Command Abstract Machines Physical Machine

8 Timesharing Systems(2) Uses multiprogramming Support interactive computing model (Illusion of multiple consoles) Different scheduling & memory allocation strategies than batch Tends to propagate processes Considerable attention to resource isolation (security & protection) Tend to optimize response time Computing today: Networks LAN (Local Area Network) evolution 3Mbps (1975)! 10 Mbps (1980)! 100 Mbps (1990)! 1 Gbps (2000) High speed communication means new way to do computing Shared files Shared memory Shared procedures/objects??? Computing today: Distributed OS Computing today: Distributed OS Wave of the future App App App App App App Distributed OS Multiple Computers connected by a Network

9 Computing today: Distributed OS Computing today: Web OS Course road-map Step1. Dedicated systems A variety of OS...

10 Step1. Dedicated systems Step 2. Trusted process systems A sprinkler system, a microwave oven, a gasoline dispenser Single-threaded systems Do not incorporate interrupts nor a CPU mode bit. Supporte a single program-in-execution at a time. Work divided into software modules (e.g., functions); Use of coroutines Step 2. Trusted process systems Computer hardware incorporate interrupts Supports schedulable units of computation Share some similarity with a modern set of threads: autonomous units of computation but with few barriers among the processes. The correct behavior of the system depends on the correct behavior of each process. Step 2. Trusted process systems The OS can control the hardware resources and thereby export an abstractmachine (process) model. This class of OS introduces multiprogramming, concurrency, synchronization, scheduling, and so on. It does not depend on the CPU mode bit: the OS can support the process model, but any process can read/write the address space of any other process. The correct operation of the entire system depends on the safe operation of every abstract machine (process) in the system.

11 Step 3. Managed process systems Step 3. Managed process systems Unix and Windows operating systems. Supported by mode bit (user mode/kernel mode) Idea of a process execution environment accompanied by one or more threads of execution within the process. The activity in one process is explicitly prevented from interfering with the execution environment in other processes (managed process, MP). Implement safe sharing among abstract machines. Export an abstract machine, such as a process Enforce barriers (e.g., address space protection) among the abstract machines. This course road-map A classic OS course... A variety of OS...

12 This course road-map