Outline. CSCI 4730 Operating Systems. Questions. What is an Operating System? Computer System Layers. Computer System Layers

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1 Outlie CSCI 4730 s! What is a s?!! System Compoet Architecture s Overview Questios What is a?! What are the major operatig system compoets?! What are basic computer system orgaizatios?! How do you commuicate with the operatig systems?! What services does a operatig system provide?! A program that acts as a itermediary betwee a of a computer ad the computer hardware.» Execute programs ad make solvig problems easier.! Operatig system goals:» Make the computer system coveiet to use.» Use the computer hardware i a efficiet maer.» Combiatio of the above. 3 4 system ca be divided roughly i four compoets:!! Operatig system! Applicatio programs compiler assembler text editor! Users System ad Applicatio Programs! :» provides basic computer resources: CPU, Memory, I/O Devices System ad Applicatio Programs compiler assembler text editor 5 6

2 !! Operatig system:» Cotrols ad coordiates use of hardware amog various applicatios ad s. compiler assembler text editor System ad Applicatio Programs!! Operatig system! Applicatio programs» defie the ways i which the system resources are used to solve the computig problems of the s Word processors, compilers, web browsers, database systems, video games compiler assembler text editor System ad Applicatio Programs 7 8!! Operatig system! Applicatio programs! Users» People, machies, other computers compiler assembler text editor System ad Applicatio Programs system ca be divided roughly i four compoets:!! Operatig system! Applicatio programs! Users System ad Applicatio Programs compiler assembler text editor 9 0 What Do s Do? What Makes up the?! OS is a resource allocator» Maages all resources» Decides betwee coflictig requests for efficiet ad fair resource use! OS is a cotrol program» Cotrols executio of programs to prevet errors ad improper use of the computer! No uiversally accepted defiitio!! Everythig a vedor ships whe you order a operatig system is good approximatio But varies wildly! is the Kerel» the oe program ruig at all times o the computer» everythig else is either a system program (ships with the operatig system) or a applicatio program

3 Startup CMOS/BIOS Cofiguratio Utility! A bootstrap program (iitial program) is loaded at powerup or reboot» Stored i firmware i ROM/EEROM» Stored o a chip o the motherboard (paretboard)! Iitializes all aspects of system! Loads operatig system kerel ad starts executio! Petium iitial boot strap program called the system Basic Iput Output System or BIOS. 3 4 Bootig from hard disk Etire Disk & Bootig Disk is divided ito + partitios: oe file system per partitio Etire Disk: File System: Partitio Table MBR Partitio Partitio Partitio Free Space Maagemet Boot block Super Block i-list Data blocks for files, directories, etc.! Master Boot Record (sector 0) - Petium» used to boot computer! Partitio Table» starig ad edig address of each partitio! A program (e.g. the system Basic Iput Output System or BIOS for Petiums) reads i ad executes the MBR» searches for first active partitio (oted i the partitio table)» reads i its first block (the boot block) ad executes it. Partitio Table i-ode i-ode i-ode i-ode 5 MBR Partitio Partitio Partitio 6 Partitio Layout System Orgaizatio! Boot block:» cotais a hardware specific program that is called automatically to load UNIX at system startup time! Super block:» file system type, #blocks i file system! Free space maagemet (two lists):» a chai of free data block umbers» a chai of free i-ode umbers! i-list/i-ode table:» admiistrative iformatio about a file (meta-data: ame, type, locatio, size, protectio bits, ) structured ito a array: iode table or simply the i-list» A i-ode umber: uiquely idetifies a file i a file system is a idex to the i-ode table Boot block Super Block i-list Data blocks for files, directories, etc. Free Space Maagemet 7! Oe or more CPUs, device cotrollers coect through commo bus providig access to shared memory! Cocurret executio of CPUs ad devices competig for memory cycles 8

4 System Operatios Iterrupts! CPU: the processor that perform the actual computatio! I/O cotrollers:» take commads i registers, geerate flags ad iterrupts» each device cotroller: is i charge of a particular device type has a local buffer for I/O! CPU moves data from/to mai memory to/from local buffers.! I/O is from the device to local buffer of cotroller.! Occurrece of a evet is sigaled by iterrupts either by software or hardware! A trap is a software-geerated iterrupt caused either by a error or a request.! Moder operatig systems are iterrupt drive.! Device cotroller iforms CPU that it has fiished its operatio by causig a iterrupt. 9 0 Commo Fuctios of Iterrupts Iterrupt Hadlig! Whe the CPU is iterrupted it stops what it is doig ad trasfer executio to a fixed locatio i memory» This locatio a idex to a service routie to hadle the iterrupt.! Iterrupt trasfers cotrol to the iterrupt service routie geerally, through the iterrupt vector, which cotais the addresses of all the service routies.! Iterrupt architecture must save the address of the iterrupted istructio.! Icomig iterrupts are disabled while aother iterrupt is beig processed to prevet a lost iterrupt.! The operatig system preserves the state of the CPU by storig registers ad the program couter.! Determies which type of iterrupt has occurred:» pollig» vectored iterrupt system! Separate segmets of code determie what actio should be take for each type of iterrupt Iterrupt Timelie I/O Structure! Sychroous I/O: After I/O starts, cotrol returs to program oly upo I/O completio.» Wait istructio idles the CPU util the ext iterrupt» Wait loop (cotetio for memory access).» At most oe I/O request is outstadig at a time, o simultaeous I/O processig.! Asychroous I/O: After I/O starts, cotrol returs to program without waitig for I/O completio.» System call request to the operatig system to allow to wait for I/O completio.» Device-status table cotais etry for each I/O device idicatig its type, address, ad state. 3» Operatig system idexes ito I/O device table to determie device status ad to modify table etry to iclude iterrupt. 4

5 Two I/O Methods Device-Status Table Sychroous Asychroous 5 6 Direct Memory Access Structure Storage Structure! Used for high-speed I/O devices able to trasmit iformatio at close to memory speeds.! Device cotroller trasfers blocks of data from buffer storage directly to mai memory without CPU itervetio.! Oly oe iterrupt is geerated per block, rather tha the oe iterrupt per byte.! Mai memory oly large storage media that the CPU ca access directly.! Secodary storage extesio of mai memory that provides large ovolatile storage capacity.! Magetic disks rigid metal or glass platters covered with magetic recordig material» Disk surface is logically divided ito tracks, which are subdivided ito sectors.» The disk cotroller determies the logical iteractio betwee the device ad the computer. 7 8 Storage Hierarchy Cachig! Storage systems orgaized i hierarchy.» Speed» Cost» Volatility! Cachig copyig iformatio ito faster storage system; mai memory ca be viewed as a last cache for secodary! Use of high-speed memory to hold recetly-accessed data.! Performed at may levels i a computer (i hardware, operatig system, software)! Iformatio i use copied from slower to faster storage temporarily! Faster storage (cache) checked first to determie if iformatio is there» If it is, iformatio used directly from the cache (fast)» If ot, data copied to cache ad used there! Cache smaller tha storage beig cached» Cache maagemet importat desig problem» Cache size ad replacemet policy 9 30

6 Performace of Various Levels of Storage Migratio of Iteger A from Disk to Register! Multitaskig eviromets must be careful to use most recet value, o matter where it is stored i the storage hierarchy 3! Multiprocessor eviromet must provide cache coherecy i hardware such that all CPUs have the most recet value i their cache! Distributed eviromet situatio eve more complex» Several copies of a datum ca exist» Various solutios covered i Chapter 7 3 Multi-programmig Timesharig (Multitaskig) Multiprogrammig eeded for efficiecy! Sigle caot keep CPU ad I/O devices busy at all times! Multiprogrammig orgaizes jobs (code ad data) so CPU always has oe to execute! A subset of total jobs i system is kept i memory! Oe job selected ad ru via job schedulig! Whe it has to wait (for I/O for example), OS switches to aother job memory layout Timesharig (multitaskig) is logical extesio i which CPU switches jobs so frequetly that s ca iteract with each job while it is ruig, creatig iteractive computig! Respose time should be < secod! Each has at least oe program executig i memory!process! If several jobs ready to ru at the same time! CPU schedulig! If processes do t fit i memory, swappig moves them i ad out to ru! Virtual memory allows executio of processes ot completely i memory Protectio Dual-Mode Operatio! Dual-Mode Operatio! I/O Protectio! Memory Protectio! CPU Protectio! Dual-mode operatio allows OS to protect itself ad other system compoets» User mode ad kerel/moitor mode» Mode bit (0 or ) provided by hardware Provides ability to distiguish whe system is ruig code or kerel code Some istructios desigated as privileged, oly executable i kerel mode System call chages mode to kerel, retur from call resets it to Iterrupt/fault kerel set mode 35 36

7 Trasitio from User to Kerel Mode I/O Protectio! Timer to prevet ifiite loop / process hoggig resources» Set iterrupt after specific period» Operatig system decremets couter» Whe couter zero geerate a iterrupt» Set up before schedulig process to regai cotrol or termiate program that exceeds allotted time! All I/O istructios are privileged istructios.! Must esure that a program could ever gai cotrol of the computer i kerel mode (i.e., a program that, as part of its executio, stores a ew address i the iterrupt vector). System call to perform I/O (recall moitor mode is the same as kerel mode) Memory Protectio CPU Protectio! Must provide memory protectio at least for the iterrupt vector ad the iterrupt service routies.! I order to have memory protectio, add two registers that determie the rage of legal addresses a program may access:» Base register holds the smallest legal physical memory address.» Limit register cotais the size of the rage! Memory outside the defied rage is protected.! Timer iterrupts computer after specified period to esure operatig system maitais cotrol.» Timer is decremeted every clock tick.» Whe timer reaches the value 0, a iterrupt occurs.! Timer commoly used to implemet time sharig.! Time also used to compute the curret time.! Load-timer is a privileged istructio A s Core Tasks Process Maagemet! Process Maagemets! Memory Maagemets! File Maagemets! I/O System Maagemets! Protectio System! A process is a program i executio (a active etity, i.e. a ruig program )» Basic uit of work o a computer» Examples: compilatio process, word processig process» A process eeds certai resources: e.g. CPU time, memory, files, I/O devices to accomplish its task! Each ca ru may processes at oce (e.g. usig &)» Oe process: cat file file &» Two processes: ls wc -l! A time sharig system (such as UNIX) ru several processes by multiplexig betwee them 4 4

8 Process Maagemet Activities Memory Maagemet The operatig system is resposible for the followig activities i coectio with process maagemet:! Programs become processes whe they are loaded ito memory ad start executig.» All data i memory before ad after processig! Creatig ad deletig both ad system processes! Suspedig ad resumig processes! Providig mechaisms for process sychroizatio! Providig mechaisms for process commuicatio! Providig mechaisms for deadlock hadlig» All istructios i memory i order to execute! Memory maagemet determies what is i memory whe» Optimizig CPU utilizatio ad computer respose to s! Memory maagemet activities» Keepig track of which parts of memory are curretly beig used ad by whom Job Job Job 3 Operatig System Memory Partitios» Decidig which processes (or parts thereof) ad data to move ito ad out of memory» Allocatig ad deallocatig memory space as eeded File Maagemet Mass-Storage Maagemet! OS provides uiform, logical view of iformatio storage» Abstracts physical properties to logical storage uit A File : OS maps logical files to physical devices» Each medium is cotrolled by device (i.e., disk drive, tape drive) Varyig properties iclude access speed, capacity, data-trasfer rate, access method (sequetial or radom)! File-System maagemet» Files usually orgaized ito directories» Access cotrol o most systems to determie who ca access what» OS activities iclude Creatig ad deletig files ad directories Primitives to maipulate files ad dirs maria Mappig files oto secodary storage Backup files oto stable (o-volatile) storage media uga home tucker gtech 45! Mai memory is volatile ad limited i size» Use disks to store overflow ad data that eeds to be persistet.! Disks are slower tha mai memory ad processors» Etire speed of computer operatio higes o disk subsystem ad its algorithms! OS mass storage maagemet activities:» Free-space maagemet» Storage allocatio» Disk schedulig! Some storage eed ot be fast» Tertiary storage icludes optical storage, magetic tape» Still must be maaged» Varies betwee WORM (write-oce, read-may-times) ad RW (read-write) 46 I/O Subsystem Maagemet Protectio ad Security! Oe purpose of OS is to hide peculiarities of hardware devices from the! I/O subsystem resposible for» Memory maagemet of I/O icludig bufferig (storig data temporarily while it is beig trasferred), cachig (storig parts of data i faster storage for performace), spoolig (the overlappig of output of oe job with iput of other jobs)» Geeral device-driver iterface» Drivers for specific hardware devices! Protectio ay mechaism for cotrollig access of processes or s to resources defied by the OS! Security defese of the system agaist iteral ad exteral attacks» Huge rage, icludig deial-of-service, worms, viruses, idetity theft, theft of service! Systems geerally first distiguish amog s, to determie who ca do what» User idetities ( IDs, security IDs) iclude ame ad associated umber, oe per» User ID the associated with all files, processes of that to determie access cotrol» Group idetifier (group ID) allows set of s to be defied ad cotrols maaged, the also associated with each process, file» Privilege escalatio allows to chage to effective ID with more rights 47 48

9 Computig Eviromets Computig Eviromets (Cot.)! Traditioal computer» Blurrig over time» Office eviromet PCs coected to a etwork, termials attached to maiframe or miicomputers providig batch ad timesharig Now portals allowig etworked ad remote systems access to same resources» Home etworks Used to be sigle system, the modems Now firewalled, etworked! Cliet-Server Computig» Dumb termials supplated by smart PCs» May systems ow servers, respodig to requests geerated by cliets Compute-server provides a iterface to cliet to request services (i.e. database) File-server provides iterface for cliets to store ad retrieve files Peer-to-Peer Computig Web-Based Computig! Aother model of distributed system! Web has become ubiquitous! PP does ot distiguish cliets ad servers» Istead all odes are cosidered peers» May each act as cliet, server or both! Node must joi PP etwork» Registers its service with cetral lookup service o etwork, or» Broadcast request for service ad respod to requests for service via discovery protocol! PCs most prevalet devices! More devices becomig etworked to allow web access! New category of devices to maage web traffic amog similar servers: load balacers! Use of operatig systems like Widows 95, cliet-side, have evolved ito Liux ad Widows XP, which ca be cliets ad servers! Examples iclude Napster ad Gutella 5 5 Summary! A (from here o OS) is a software (a program) that performs two fuctios:» it exteds the use of the computer hardware ad» it maage the computer system resources 53