Operating Systems:Basic Concepts and History 1Introduction to Operating SystemsAn operating system is the interface between the user and the architecture.User ApplicationsOS as juggler: providing the illusion of a dedicated machine with infinite memory and CPU.OS ttti f hth ll tiOperating SystemHardwareVirtual Machine InterfacePhysical Machine Interface2OS as government: protecting users from each other, allocating resources efficiently and fairly, and providing secure and safe communicationOS as complex system: keeping OS design and implementation as simple as possible is the key to getting the OS to workWhat is an Operating System?Any code that runs with the hardware kernel bit set¾ An abstract virtual machine¾ A set of abstractions that simplify application designFiles instead of“bytes on a disk”Files instead of bytes on a diskCore OS services, written by “pros”¾ Processes, process scheduling¾ Address spaces¾ Device control¾ ~30% of Linux source code. Basis of stability and securityDevice drivers written by “whoever”¾Software run in kernel to manages a particular vendor’s3¾Software run in kernel to manages a particular vendor s hardware E.g. Homer Simpson doll with USB ¾ ~70% of Linux source code¾ OS is extensible¾ Drivers are the biggest source of OS instabilityWhat is an Operating System?For any OS area (CPU scheduling, file systems, memory management), begin by asking two questions¾ What’s the hardware interface? (The Physical Reality)¾What is the application interface? (The Nicer Interface for¾What is the application interface? (The Nicer Interface for programmer producivity)Key questions:¾ Why is the application interface defined the way it is?¾ Should we push more functionality into applications, the OS, or the hardware?¾ What are the tradeoffs between programmability, complexity, and flexibility?4flexibility?Operating System FunctionsService provider¾ Provide standard facilities  File system Standard librariesWi d tWindow system …Coordinator: three aspects¾ Protection: prevent jobs from interfering with each other¾ Communication: enable jobs to interact with each other¾ Resource management: facilitate sharing of resources across jobs.Operating systems are everywhere¾Singlefunction devices (embedded controllers Nintendo )5¾Single-function devices (embedded controllers, Nintendo, …) OS provides a collection of standard services Sometimes OS/middleware distinction is blurry¾ Multi-function/application devices (workstations and servers) OS manages application interactionsWhy do we need operating systems?Convenience¾ Provide a high-level abstraction of physical resources.Make hardware usable by getting rid of warts & specificsMake hardware usable by getting rid of warts & specifics.¾ Enable the construction of more complex software systems¾ Enable portable code. MS-DOS version 1 boots on the latest 3+ GHz Pentium. Would games that ran on MS-DOSv1 work well today?Efficiency6y¾ Share limited or expensive physical resources.¾ Provide protection.Computer Architecture & ProcessesCPU -the processor that performs the actual computation 7CPU the processor that performs the actual computation I/O devices - terminal, disks, video board, printer, etc. Memory - RAM containing data and programs used by the CPU System bus - the communication medium between the CPU, memory, and peripheralsEvolution of Operating SystemsWhy do operating systems change?¾ Key functions: hardware abstraction and coordination¾ Principle: Design tradeoffs change as technology changes.Comparing computing systems from 1981 and 2007Comparing computing systems from 1981 and 20071981 2007 FactorMIPS 1 57,000 57,000$/SPECInt $100K $2 50,000DRAM size 128KB 2GB 16,000Disk size 10MB 1TB 100,000Net BW9600 bps100 Mb/s10 0008Net BW9600 bps100 Mb/s10,000Address bits 16 64 4Users/machine 100 <1 100Energy efficiency and parallelism loom on the horizon.Data centers projected to consume 3% of US energy by next yearNo more single-core CPUsFrom Architecture to OS to Application, and BackHardware Example OS Services User AbstractionProcessor Process management, Scheduling, Traps, Processg, p ,Protections, Billing, SynchronizationMemory Management, Protection, Virtual memoryAddress spaceI/O devices Concurrency with CPU, Interrupt handlingTerminal, Mouse, Printer, (System Calls)9Calls)File system Management, Persistence FilesDistributed systemsNetwork security, Distributed file systemRPC system calls, Transparent file sharingFrom Architectural to OS to Application, and BackOS Service Hardware SupportProtection Kernel / User modeProtected InstructionsProtected InstructionsBase and Limit RegistersInterrupts Interrupt VectorsSystem calls Trap instructions and trap vectorsI/O Interrupts or Memory-MappingScheduling error Timer10Scheduling, error recovery, billingTimerSynchronization Atomic instructionsVirtual Memory Translation look-aside buffersRegister pointing to base of page tableInterrupts - Moving from Kernel to User ModeUser processes may not:address I/O directlyuse instructions that manipulate OS memory py(e.g., page tables)set the mode bits that determine user or kernel modedisable and enable interruptshalt the machine11but in kernel mode, the OS does all these thingsa status bit in a protected processor register indicates the modeProtected instructions can only be executed in kernel mode.On interrupts (e.g., time slice) or system callsHistory of Operating Systems: PhasesPhase 1: Hardware is expensive, humans are cheap¾ User at console: single-user systems¾ Batching systems¾Mltiit¾Multi-programming systemsPhase 2: Hardware is cheap, humans are expensive¾ Time sharing: Users use cheap terminals and share serversPhase 3: Hardware is very cheap, humans are very expensive¾ Personal computing: One system per user¾Distributed computing: lots of systems per user12¾Distributed computing: lots of systems per userPhase 4: Ubiquitous computing/Cloud computing¾ Cell phone, mp3 player, DVD player, TIVO, PDA, iPhone, eReader¾ Software as a service, Amazon’s elastic compute cloudHistory of Operating Systems: PhasesPhase 1: Hardware is expensive, humans are cheap¾ User at console: single-user systems¾ Batching systems¾Mltiit¾Multi-programming systemsPhase 2: Hardware is cheap, humans are expensive¾ Time sharing: Users use cheap terminals and share serversPhase 3: Hardware is very cheap, humans are very expensive¾ Personal computing: