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2012-12-06 CS 134: Operating Systems Definitions, Abstractions, Taxonomies, Early History 1 / 36 CS34 CS 134: Operating Systems Definitions, Abstractions, Taxonomies, Early History 2012-12-06 Overview What Is an OS? History Hardware 2 / 36 CS34 Overview What Is an OS? Overview History Hardware What Is an OS? 2012-12-06 What is an Operating System Anyway? CS34 What Is an OS? What is an Operating System Anyway? What is an Operating System Anyway? Class Exercise: Devise three separate definitions. Discuss. Several slides follow that aren’t on handout. Class Exercise: Devise three separate definitions. Discuss. 3 / 36 What Is an OS? 2012-12-06 It’s A Programmer’s Toolkit Provide useful functionality to programs: I Prevent duplicated work I Promote reuse 4 / 36 CS34 What Is an OS? It’s A Programmer’s Toolkit Provide useful functionality to programs: It’s A Programmer’s Toolkit I Prevent duplicated work I Promote reuse What Is an OS? 2012-12-06 It’s a Control Program Provide the rules for the how the machine will operate: I Control the operation of the I/O devices I Ensure smooth running of the machine 5 / 36 CS34 What Is an OS? It’s a Control Program Provide the rules for the how the machine will operate: It’s a Control Program I Control the operation of the I/O devices I Ensure smooth running of the machine What Is an OS? 2012-12-06 It’s an Abstraction Layer Make the machine “nicer”, easier to program, higher level. . . I Hide some of the idiosyncrasies of the machine I Provide functionality the underlying machine doesn’t have User Application Operating System Hardware 6 / 36 CS34 What Is an OS? It’s an Abstraction Layer It’s an Abstraction Layer Make the machine “nicer”, easier to program, higher level. . . I Hide some of the idiosyncrasies of the machine I Provide functionality the underlying machine doesn’t have User Application Operating System Hardware dynamic view that traces the progress of a user event through the system. A typical event in Mac C H A P T E R OSOS? X originates when the user manipulates an input device such as a mouse or a keyboard. The What Is an It’s an Abstraction Layer A Layered Perspective 3 System Architecture The Core Services and Application Services layers and the Carbon and Cocoa application environments are packaged in umbrella frameworks (described in the chapter “Umbrella Frameworks” (page 97)). Many public APIs of the kernel environment are exported through headers found in /usr/include. 2012-12-06 device driver associated with that device, through the I/O Kit, creates a low-level event, puts it in the window server’s event queue, and notifies the window server. The window server dispatches the event to the appropriate run-loop port of the target process. There the event is picked up by the Carbon Event Manager and forwarded to the event-handling mechanism appropriate to the application environment. Events can also be asynchronous, such as a network packet containing configuration changes. CS34 What Is an OS? The first part of this chapter, as summarized in the foregoing paragraphs, presents the architecture of Mac OS X as layers of system software. Following this static perspective of Mac OS X is a more dynamic view that traces the progress of a user event through the system. A typical event in Mac OS X originates when the user manipulates an input device such as a mouse or a keyboard. The device driver associated with that device, through the I/O Kit, creates a low-level event, puts it in the window server’s event queue, and notifies the window server. The window server dispatches the event to the appropriate run-loop port of the target process. There the event is picked up by the Carbon Event Manager and forwarded to the event-handling mechanism appropriate to the application environment. Events can also be asynchronous, such as a network packet containing configuration changes. It’s an Abstraction Layer A Layered Perspective A common way to look at complex software is to separate out parts of that software into “layers.” Make the machine “nicer”, easier to one program, higher level. . .layer on the bottom. Visually depicted, layer sits on top of another, with the most fundamental This kind of diagram suggests the general interfaces and dependencies between the layers of I software. The higher layers of software, which are the closest to actual application code, depend Hide some of the idiosyncrasies ofunder the machine on the layer immediately them, and that intermediate layer depends on an even lower I OS X is reducible to suchmachine a perspective. Figure 3-1 (page 40) illustrates the general structure Provide functionality theofMacunderlying doesn’t have Mac OS X system software as interdependent layers of libraries, frameworks, and services. layer. It’s an Abstraction Layer Figure 3-1 Mac OS X as layers of system software Application environment Classic User Application Carbon Cocoa Java (JDK) Application Services Operating System BSD BSD QuickTime Core Services Kernel environment Hardware Although this diagram does help clarify the overall architecture, there are dangers in the necessarily over-simplified view it presents. The Mac OS X services and subsystems that one application uses—and how it uses them—can be very different from those used by another application, even one of a similar type. Dependencies and interfaces at the different levels can vary from program to program depending on individual requirements and realities. With that caveat aside, let’s take a guided tour through the layers depicted in this diagram. A common way to look at complex software is to separate out parts of that software into “layers.” Make the machine “nicer”, easier to one program, higher level. . .layer on the bottom. Visually depicted, layer sits on top of another, with the most fundamental This kind of diagram suggests the general interfaces and dependencies between the layers of software. The higher layers of software, which are the closest to actual application code, depend on the layer immediately under them, and that intermediate layer depends on an even lower layer. I Hide some of the idiosyncrasies of the machine I OS X is reducible to suchmachine a perspective. Figure 3-1 (page 40) illustrates the general structure Provide functionality theMac underlying doesn’t have of Mac OS X system software as interdependent layers of libraries, frameworks, and services. Figure 3-1 Mac OS X as layers of system software Application environment Classic User Application Carbon Cocoa Java (JDK) Application Services Operating System BSD BSD QuickTime Core Services Kernel environment Hardware Although this diagram does help clarify the overall architecture, there are dangers in the necessarily over-simplified view it presents. The Mac OS X services and subsystems that one application uses—and how it uses them—can be very different from those used by another application, even one of a similar type. Dependencies and interfaces at the different levels can vary from program to program depending on individual requirements and realities. With that caveat aside, let’s take a guided tour through the layers depicted in this diagram. 40 A Layered Perspective © Apple Computer, Inc. 2003 6 / 36 40 A Layered Perspective © Apple Computer, Inc. 2003 What Is an OS? 2012-12-06 It’s a Virtual Machine OS provides an environment This environment can be seen as a “new machine”. . . Hardware —Physical machine + Core OS —Virtual machine + OS Libraries + OS Utilities + Application —Virtual machine —Virtual machine —Virtual machine 7 / 36 CS34 What Is an OS? It’s a Virtual Machine OS provides an environment This environment can be seen as a “new machine”. . . Hardware It’s a Virtual Machine —Physical machine + Core OS —Virtual machine + OS Libraries + OS Utilities + Application —Virtual machine —Virtual machine —Virtual machine What Is an OS? 2012-12-06 It’s a Protection Layer Make the machine more robust—less scope for a bug to have devastating consequences I OS does everything programs can’t be trusted to do I OS makes programs play nice with others 8 / 36 CS34 What Is an OS? It’s a Protection Layer Make the machine more robust—less scope for a bug to have devastating consequences It’s a Protection Layer I OS does everything programs can’t be trusted to do I OS makes programs play nice with others What Is an OS? 2012-12-06 It’s a Policy Enforcer OS provides the mechanisms to enforce various policies 9 / 36 CS34 What Is an OS? It’s a Policy Enforcer OS provides the mechanisms to enforce various policies It’s a Policy Enforcer What Is an OS? 2012-12-06 It’s a Policy Enforcer OS provides the mechanisms to enforce various policies Class Exercise: Examples? 9 / 36 CS34 What Is an OS? It’s a Policy Enforcer OS provides the mechanisms to enforce various policies It’s a Policy Enforcer Class Exercise: Examples? What Is an OS? 2012-12-06 It’s a Resource Manager The operating system manages physical resources: I Processor I Memory I Storage devices I Network devices etc. . . 10 / 36 CS34 What Is an OS? It’s a Resource Manager The operating system manages physical resources: It’s a Resource Manager I Processor I Memory I Storage devices I Network devices etc. . . What Is an OS? 2012-12-06 It’s a Resource Manager (cont’d.) The operating system manages virtual resources: I Processes I Files I Users I Network connections I Windows etc.. . . 11 / 36 CS34 What Is an OS? It’s a Resource Manager (cont’d.) It’s a Resource Manager (cont’d.) The operating system manages virtual resources: I Processes I Files I Users I Network connections I Windows etc.. . . What Is an OS? 2012-12-06 It’s a Product Many operating systems are sold by commercial companies I Market vs. technical considerations I The operating system is what comes in the box marked “operating system” 12 / 36 CS34 What Is an OS? It’s a Product Many operating systems are sold by commercial companies It’s a Product I Market vs. technical considerations I The operating system is what comes in the box marked “operating system” What Is an OS? 2012-12-06 Fundamental Abstractions What are the (user-level) abstractions we’d expect to find in a modern OS? 13 / 36 CS34 What Is an OS? Fundamental Abstractions Fundamental Abstractions What are the (user-level) abstractions we’d expect to find in a modern OS? What Is an OS? 2012-12-06 Fundamental Abstractions Include. . . I I System calls Processes I I I I I I I I I I I Files Directories Filesystems Events Asynchronous Synchronous IPC Mechanisms I Threads Address spaces Files I I Communications channels I I I I Semaphores Mutexes Condition Variables Pipelines Network connections Users (Remote) Hosts 14 / 36 CS34 What Is an OS? Fundamental Abstractions Include. . . I I System calls Processes I Files I I Fundamental Abstractions I I I I I IPC Mechanisms I Communications channels I I I Files Directories Filesystems Events I I Threads Address spaces Asynchronous Synchronous I I I I Semaphores Mutexes Condition Variables Pipelines Network connections Users (Remote) Hosts What Is an OS? 2012-12-06 It’s a Resource Manager What are the “resources” that an operating system manages? 15 / 36 CS34 What Is an OS? It’s a Resource Manager What are the “resources” that an operating system manages? It’s a Resource Manager What Is an OS? 2012-12-06 It’s a Resource Manager The operating system manages physical resources: I Processor I Memory I Storage devices I Network devices etc.. . . 16 / 36 CS34 What Is an OS? It’s a Resource Manager The operating system manages physical resources: It’s a Resource Manager I Processor I Memory I Storage devices I Network devices etc.. . . What Is an OS? 2012-12-06 It’s a Resource Manager (cont’d.) The operating system manages virtual resources: I Processes I Files I Users I Network connections I Windows etc.. . . 17 / 36 CS34 What Is an OS? It’s a Resource Manager (cont’d.) It’s a Resource Manager (cont’d.) The operating system manages virtual resources: I Processes I Files I Users I Network connections I Windows etc.. . . What Is an OS? 2012-12-06 Taxonomy of Computer Systems Different computer systems ask different things from their OS 18 / 36 CS34 What Is an OS? Taxonomy of Computer Systems Different computer systems ask different things from their OS Taxonomy of Computer Systems What Is an OS? 2012-12-06 Taxonomy of Computer Systems Different computer systems ask different things from their OS Class Exercise: Give some dimensions across which computer systems vary 18 / 36 CS34 What Is an OS? Taxonomy of Computer Systems Different computer systems ask different things from their OS Taxonomy of Computer Systems Class Exercise: Give some dimensions across which computer systems vary What Is an OS? 2012-12-06 Partial Taxonomy of Computer Systems Different computer systems ask different things from their OS: Special-purpose Single-user Non–Resource-sharing Single processor Stand alone Centralized Batch Deadline-free Insecure Symmetric Simple Small Inexpensive ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ etc. General-purpose Multi-user Resource sharing Multiprocessor Networked Distributed Interactive Real-time Secure Asymmetric Complex Large Expensive 19 / 36 CS34 What Is an OS? Partial Taxonomy of Computer Systems Partial Taxonomy of Computer Systems Different computer systems ask different things from their OS: Special-purpose Single-user Non–Resource-sharing Single processor Stand alone Centralized Batch Deadline-free Insecure Symmetric Simple Small Inexpensive ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ ↔ etc. General-purpose Multi-user Resource sharing Multiprocessor Networked Distributed Interactive Real-time Secure Asymmetric Complex Large Expensive History 2012-12-06 Early Computers 1950s—large complex machines I Operated directly from a console I Used interactively by a single user I Ran one program at a time (uniprogramming) I Read data from paper tape, punched cards, or toggle switches OS? Maybe a library containing code to work the I/O devices was useful. 20 / 36 CS34 History Early Computers 1950s—large complex machines I Early Computers Operated directly from a console I Used interactively by a single user I Ran one program at a time (uniprogramming) I Read data from paper tape, punched cards, or toggle switches OS? Maybe a library containing code to work the I/O devices was useful. History 2012-12-06 Simple Batch Systems Provide better use of resources: I Users access computer indirectly I Programs and input (jobs) taken from a batch queue I Computer has a human operator to feed it jobs Card reader Tape drive Input tape System tape Output tape Printer 1401 7094 1401 Need to: I Manage the jobs: I Protect the next program from the previous program 21 / 36 CS34 History Simple Batch Systems Provide better use of resources: I Users access computer indirectly I Programs and input (jobs) taken from a batch queue I Computer has a human operator to feed it jobs Card reader Simple Batch Systems Tape drive Input tape System tape Output tape Printer 1401 7094 1401 Need to: I Manage the jobs: I Protect the next program from the previous program History 2012-12-06 SPOOLing Batch Systems Provide better use of resources—buffer input and output I Read-ahead input from disk/tape I Write-behind output to disk/tape 22 / 36 CS34 History SPOOLing Batch Systems Provide better use of resources—buffer input and output SPOOLing Batch Systems I Read-ahead input from disk/tape I Write-behind output to disk/tape History 2012-12-06 SPOOLing Batch Systems Provide better use of resources—buffer input and output I Read-ahead input from disk/tape I Write-behind output to disk/tape Class Exercise: Why does buffering improve performance? Does buffering always improve performance? (What assumptions are we making?) 22 / 36 CS34 History SPOOLing Batch Systems Provide better use of resources—buffer input and output SPOOLing Batch Systems I Read-ahead input from disk/tape I Write-behind output to disk/tape Class Exercise: Why does buffering improve performance? Does buffering always improve performance? (What assumptions are we making?) History 2012-12-06 Multiprogrammed Batch Systems Provide better use of resources—multiplex the processor: I Run multiple independent programs at once I Switch to another program when running program waits for I/O More work for OS. More complex management of I I/O I Memory I Processor 23 / 36 CS34 History Multiprogrammed Batch Systems Provide better use of resources—multiplex the processor: Multiprogrammed Batch Systems I Run multiple independent programs at once I Switch to another program when running program waits for I/O More work for OS. More complex management of I I/O I Memory I Processor History 2012-12-06 Time-Sharing Systems Provide better environment for users—multiplex the processor between users: I I Run multiple independent programs at once Switch between users rapidly I Illusion of having the machine’s full attention Yet more complexity for OS: 24 / 36 CS34 History Time-Sharing Systems Provide better environment for users—multiplex the processor between users: I Time-Sharing Systems I Run multiple independent programs at once Switch between users rapidly I Illusion of having the machine’s full attention Yet more complexity for OS: History 2012-12-06 History Repeats Itself As new, “smaller” hardware appears, it tends to repeat this evolution I Mini computers I Personal computers I PDAs Embedded systems I I I I Cell phones MP3 Players Cameras, etc. 25 / 36 CS34 History History Repeats Itself As new, “smaller” hardware appears, it tends to repeat this evolution History Repeats Itself I Mini computers I Personal computers I PDAs Embedded systems I I I I Cell phones MP3 Players Cameras, etc. Hardware disk disk printer 2012-12-06 Computer Hardware tape drives on-line CS34 Hardware Computer Hardware disk disk printer CPU printer controller Computer Hardware disk controller printer controller tape-drive controller system bus memory controller memory 26 / 36 tape-drive controller system bus memory controller memory CPU tape drives on-line disk controller Hardware 2012-12-06 Computer Hardware—CPU & Memory Need to perform computation! Start I I Fetch Instruction Execute Instruction Memory contains program instructions and program data Processor registers maintain processor state. Registers include: I I I I General purpose (address & data) registers Instruction pointer (aka program counter) Stack pointer(s) Control and status registers 27 / 36 CS34 Hardware Computer Hardware—CPU & Memory Need to perform computation! Start Computer Hardware—CPU & Memory I I Fetch Instruction Execute Instruction Memory contains program instructions and program data Processor registers maintain processor state. Registers include: I I I I General purpose (address & data) registers Instruction pointer (aka program counter) Stack pointer(s) Control and status registers Hardware 2012-12-06 Computer Hardware—I/O Devices Need to communicate with the world! I I/O devices and CPU execute concurrently I Devices have hardware controllers I I I I I/O is from the device to local buffer of controller disk printer tape drives on-line CPU disk controller printer controller Computer Hardware—I/O Devices Need to communicate with the world! I I/O devices and CPU execute concurrently I Devices have hardware controllers I I I I Handles devices of a particular device type Some level of autonomy Local buffer I/O is from the device to local buffer of controller Computer Hardware—I/O Devices disk disk printer tape-drive controller system bus memory controller memory 28 / 36 tape drives on-line CPU disk controller printer controller tape-drive controller system bus memory controller memory Handles devices of a particular device type Some level of autonomy Local buffer disk CS34 Hardware Hardware 2012-12-06 Programmed I/O After I/O starts, control returns to user program only on I/O completion I I CPU waits until I/O completes. At most one I/O request is outstanding at a time I No simultaneous I/O processing 29 / 36 CS34 Hardware Programmed I/O After I/O starts, control returns to user program only on I/O completion I Programmed I/O I CPU waits until I/O completes. At most one I/O request is outstanding at a time I No simultaneous I/O processing Hardware 2012-12-06 Polled I/O Polling == Querying the I/O device Separate I/O into two parts: I Initiation I Polling Advantages? 30 / 36 CS34 Hardware Polled I/O Polling == Querying the I/O device Separate I/O into two parts: Polled I/O I Initiation I Polling Advantages? Hardware 2012-12-06 Interrupt-Driven I/O Separate I/O into two parts: I Initiation I Asynchronous notification 31 / 36 CS34 Hardware Interrupt-Driven I/O Separate I/O into two parts: Interrupt-Driven I/O I Initiation I Asynchronous notification Hardware 2012-12-06 I/O in User-Level Code User-level code almost always uses “programmed I/O” (e.g. read and write on a file) Why? 32 / 36 CS34 Hardware I/O in User-Level Code User-level code almost always uses “programmed I/O” (e.g. read and write on a file) I/O in User-Level Code Why? Hardware 2012-12-06 Computer Hardware—CPU with Interrupts CPU needs another feature. . . Start Fetch Instruction Execute Instruction No Interrupts Enabled? Yes No Interrupt? Yes Jump to Handler Save State 33 / 36 CS34 Hardware Computer Hardware—CPU with Interrupts CPU needs another feature. . . Start Fetch Instruction Execute Instruction No Computer Hardware—CPU with Interrupts Interrupts Enabled? Yes No Interrupt? Yes Jump to Handler Save State Hardware 2012-12-06 Handling an Interrupt What needs to happen: I Save state I I I All registers Switch stacks? Find out what interrupt was. . . I I Polling Vectored interrupts 34 / 36 CS34 Hardware Handling an Interrupt What needs to happen: I Save state I I Handling an Interrupt I All registers Switch stacks? Find out what interrupt was. . . I I Polling Vectored interrupts Hardware 2012-12-06 Types of Interrupts Various types I Software exception (also called a trap) I Timer I I/O I Hardware failure A modern operating system is interrupt driven 35 / 36 CS34 Hardware Types of Interrupts Various types Types of Interrupts I Software exception (also called a trap) I Timer I I/O I Hardware failure A modern operating system is interrupt driven Hardware 2012-12-06 Other Hardware Features We’ve covered interrupts, but hardware has other cool features, including: I Caches I Memory management I Protection We’ll come back to hardware as we address these topics. 36 / 36 CS34 Hardware Other Hardware Features We’ve covered interrupts, but hardware has other cool features, including: Other Hardware Features I Caches I Memory management I Protection We’ll come back to hardware as we address these topics.
