operating systems slide 1 gaius what is an operating...

Operating Systemsslide 1gaius

What is an operating system?

"Peterson and Silbershatz"

"We can view an operating system as a resource allocator. A computersystem has many resources (hardware and software) that may berequired to solve a problem: CPU time, memory space, file storagespace, I/O devices, and so on.

The operating system acts as the manager of these resources andallocates them to specific programs and users as necessary for theirtasks. Since there may be many, possibly conflicting requests forresources, the operating system must decide which requests areallocated resources to operate the computer system efficiently andfairly."


Windows NT

many elements influenced the design of Windows NTit provides the same type of GUI found in the earlier Windowsproductsincluding the use of windowspull down menuspoint and click interaction


NT components

internal interaction is inspired by the Mach operating system, which isin turn based on UNIX

highly modular

can execute on a variety of hardware platforms

supports applications written for a variety of other operating systems

as with virtually all operating systems, NT separates applicationoriented software from operating system software. (Kernel mode anduser mode)


Design goals of NT

like any commercial operating system, Windows NT is the result of acomplex interaction between idealized goals and market-driven realities

Compatibilityit should support a wide range of existing software and legacyhardware. (DOS, Windows 3.1 compatibility)

Robustnessit should resist attacks of naive or malicious users, individualprograms should be isolated from each other

Portabilityit should run on a wide variety of current and future hardwareplatforms


Design goals of NT

Extendibilityit should be possible to add new features and support new I/Odevices

Performanceit should give reasonable performance on commonly availablehardware. Take advantage of multiprocessing hardware


Major building blocks of NT

Overall architecture of the NT kernel mode components


Hardwar e abstraction layer

HAL is a thin layer of software that presents the rest of the system withan abstract model of any hardware that is not part of the CPU

HAL exposes a well defined set of functions that manage such items as:Off chip cachesTimersI/O busesDevice registersInterrupt controllersDMA controllers

various system components use these HAL functions to interact withCPU hardware

HAL routines make the kernel and device drivers binarycompatible across platforms with the same CPU architecture

Operating Systemsslide 10

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Kernel

consists of the most fundamental components of the operating systemmanages scheduling and context switchingexception and interrupt handlingmultiprocessor synchronization

Executivethe most complex kernel mode component in Windows NTimplement many of the basic functions normally associated withan operating system(Process manager, virtual memory manager, I/O manager, systemcall interface)

the executive uses the HAL to interact with any CPU hardware


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Layered device drivers in NT

the term driver normally refers to a piece of code that manages someperipheral or device

NT takes a more flexible approachallows several driver layers to exist between an applicationprogram and hardware

Device driversmanage actual data transfer and control operations for a specifictype of physical deviceincludes starting stopping I/O, handling interrupts and handlingerrors

Intermediate drivers

NT allows you to place any number of layers on top of a physicaldevice driverintermediate layers provide a way of extending the capabilities ofthe I/O system without having to modify the drivers below them


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Example: Fault tolerant disk driver

is implemented as a layer that sits between the file system and driversfor any physical disks.

intermediate drivers separate hardware specific operations from moregeneral management issues

here the intermediate driver is referred to as aclass driverand thehardware driver is called aport driver

this structure makes it easier to target a wider range of hardwaresince only the port code needs to be rewritten


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File system drivers (FSDs)

the following FSDs are supplied by Microsoft:

Type Description

FAT Windows 95 extended MSDOS file systemNTFS Windows NT high reliability file systemHPFS OS/2high performance file systemCSFS ISO9660 CDROM file systemMSFS Mailshotfile systemNPFS Namedpipe file systemRDR LAN Manager redirector

unfortunately, you cannot develop file system drivers using thestandard NT device driver k it

also note the absence of NFS.


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Device driver


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UNIX vs NT

NT available on other architectures Alpha, Mips, Power PC

UNIX also available on other architectures, all of the above and more

NT will run all Windows 3.1 software and MSDOS software

UNIX may or may not depending on version, vendorgenerally unlikely


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UNIX vs NT

both NT and UNIX (Solaris, Sequent) will operate with multipleprocessors

both OSs have TCP/IP and associated utilities in different formsNT doesn’t hav eNFS though (which considered slow, but open!)

nevertheless much research has been done to improve NFSperformance

both OSs support filesystems with long filenames

NT will easily integrate with Novell, MACOSUNIX needs extra packages (eg samba) which has to be configuredby an expert


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UNIX vs NT

UNIX is still more flexible in resource sharingshare any peripheral across the networkall peripherals are as files, files can be on the network etc

Windows NT NTFS is faster than NFS

UNIX buffer cache is superior to NT

thus it is not clear which OS will be faster!measure it!

TCP/IP code is more mature than NT, witness problems in J111


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UNIX vs NT

NT is mucheasier to manage

NT is mucheasier to install

NT is more tolerant of different hardware devices due to the HAL


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Network Operating Systems (Unix)

UNIX started life as a research project within AT&T in 1970since that time it has grown in popularity and functionality

there are some excellent books available which describe UNIX

Berny Goodheart & James Cox,"The magic garden explained",Prentice-Hall.

Smoot Carl-Mitchell & John S. Quarterman,"PracticalInternetworking with TCP/IP and UNIX", Addison Wesley.

W.Richard Stevens,"UNIX Network Programming", Prentice-Hall.


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UNIX networking history

the first networking functionality added to UNIX wasUUCP (UNIX toUNIX copy) in 1976

provided a mechanism to transfer files from different UNIXmachines which typically only had modem connectivityimplemented was a batch-oriented system that was typically usedbetween systems

remote printing and email were added in the Berkeley release of theVersion 7 UNIX for the PDP-11 (called 2.x BSD) (Berkeley StandardDistribution)

TCP/IP was released in 1981 in the 4.1 BSD UNIX


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Unix history

TCP/IP opened the flood gates for networked applicationsNFS - network file systemremote job executionremote login, telnet, ftp, R toolstalkremote procedure calls and XDRnewsclient server computing


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UNIX networking history

the Berkeley releases of UNIX 4.1 BSD and 4.2 BSD provided the firstUNIX systems with widespread network support (1982-1983)

many Computer Science departments started to buy more than oneVAX with Ethernet cards and so created UNIX LANs

April 1986 4.3 BSD was releasedJune 1988 a revision of the 4.3 BSD referred to as the Tahoedistributionwas meant to be an interim release for testing by experienced users

importantly it contained source code which was not licensed by AT&Tso you couldlegallyuse the source code for your own productsreference software was available for TCP/IP & sockets


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UNIX network services

rexd remote job execution daemonallows a user to say:

on floppsie gcc -g largeprogram.c

theon command makes the C compiler execute on a machinecalled floppsieall input/output has to be rerouted tofloppsie in order that thecompilation will work.

telnet - the ability to login into another machine

NFS - Network file system.

RPC - Remote procedure call package (1984)

normally uses theXDR facility and it is an interprocess communicationmechanism that allows programmers to write client-server basedapplications


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UNIX networking facilities

sockets - introduced in 1982 with 4.1 BSD.Another interprocess communication mechanism (low lev el) whichallows one process to communicate with another process. Theseprocesses maybe on the same machine or on opposite sides of theworld. Sockets consist on five primitives:socket, bind, listen,connect andaccept

today hundreds of client/servers use above primitives

email (pop2, pop3, imap, smtp), news, R commands, lpd, nfs, ftp,telnet, news, finger, cvs, http


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Networking examples

pop2 emailclientpop3 emailclientimap emailserversmtp emailclientnews discussiongroupsR commands remotecommandslpd networked printingnfs networked file systemftp file transfer protocoltelnet remoteloginfinger userdescription & profilecvs networked source code accesshttp hypertext protocol


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Networking examples

examine the file/etc/services for a full description


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A typical UNIX network

UNIX is an open systemmany vendors: SUNOS, ULTRIX, AT&T UNIX SVr4,GNU/Linux, BSD386some free! (Source code, compilers, debuggers, editors, networkapplications etc)its popularity in the early days was due in part to its no costavailabilitythis has now turned full circle with the advent of GNU/Linux andBSD386

open system as interfaces to applications, client/servers are published

important to notea major difference between UNIX and otheroperating systems (Novell) is that clients and servers on UNIX lookalmost identical

possible that they are the same except for some files in/etc

(configuration files)


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client/server distinction occurs at the user level not the system level


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ethernet and IP

workstation local disk

workstation local disk

local diskworkstation

configuration isveryflexible


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Unix configuration

could be a disadvantage as system administrators have to fight theirway through many different options for various components just toperform simple operations

it is possible that all machines are configured identically (except fortheir hostname, IP address etc)

could configure the network operating systems so that all localdisks can be seen by all machines


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alternatively machines could be very different (ie could build distinctclient/server model similar to Novell)

one machine has the common file systemone machine has the system executables


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Disadvantages

complexity

flexibility requires system administrators be disciplined otherwiseoverall system may become unmanageable

when more machines are added

harder to configure than other operating systemsgetting better (Solaris, GNU/Linux brands often use Gtk)but complexity still remainsfew graphical tools to identify installation errors

however the problems are being addressed


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NFS configuration example

can network file systems between different architectureslittle endian, big endian - it makes no difference

NFS design is built from three main parts: a protocol, a server and aclient

nfs protocol nfs servernfs client


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NFS configuration example

components fit into the ISO-7 layer model

Level 7 Application NFS

Level 6 Presentation XDR

Level 5 Session RPC

Level 4 Transport TCP UDP

Level 3 Network IP

Level 2 Data Link Logical

Level 1 Physical Link Ethernet


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NFS example

suppose we have two machines

mcgregfloppsie

includebin

X386

usrhomebin

/

home usr bin

/

fred

our task is to allow machinefloppsie see directory/home/gmulley

Operating Systems

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NFS example

tell floppsie where this directory residesedit/etc/fstab on floppsie and add the following linemcgreg:/home /home/mcgreg nfs

(remote fs mount point type mount options)


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NFS example

need to tell machinemcgreg that/home is exported and thatfloppsie is allowed to see it

edit/etc/exportfs onmcgreg and add the following line/home 193.63.128.0/255.255.255.0(rw) floppsie(rw)


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Plan 9 from Bell Labs

MOVIE GOOFS AND INTERESTING FACTS LIST

Version 3.9 (October 1993)

A collection of film flubs, cinematic slip-ups,

movie mistakes, Hollywood howlers, etc etc.

Compiled by Murray Chapman and Michael Gaines

([email protected])

Found by the users of USENET.

# Plan 9 from Outer Space

- Bela Lugosi died two days into the

shooting of this turkey.

He was replaced by the director’s

wife’s chiropractor,

who was significantly taller than Lugosi,

and played the part with a cape

covering his face.

- Internationally recognised as the worst

movie ever made.


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Plan 9from Bell Labsis a network operating system and it is composedof separate machines acting as

CPU serversfile serversterminals

it is built from distinct specialised componentsrather than similar general purpose components

high performance general purpose components cost a lot of moneyworkstations are too slow and IO bound for fast compilationtoo expensive just to be used as a windowing system


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Plan 9 approach is based on distributed specialisation would betteraddress issues:

cost effectivenessmaintenanceperformancereliability and security


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radical steps takenbuild a completely new systemC compiler, operating system, network software, commandinterpreter, window system and terminal!

authors credentials?Rob Pike - famous for many of UNIX concepts during the earlyyearsKen Thompson - wrote the first C compiler. Then worked ontranslating UNIX from assembler to CAT&T - birth place of UNIX - so wealthy that the USA dividedAT&T into two because of its power


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Plan 9

different from other research and commercial operating systems. Itlacks features often associated with other research network operatingsystems

process migrationlightweight processesdistributed file cachingpersonalised workstationssupport for X windows


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Plan 9

built around CPU servers (large multiprocessors)file serversterminals (bitmap screen, mouse & computer running a windowsystem 8 1/2)

sharing of computing and storage services provide a sense ofcommunity for a group of programmers

cost effectivesimplifies management and administration


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CPU Servers

in 1990 the production CPU server was a Silicon Graphics PowerSeries machine with four 25 MHz MIPS processors

128 Mbyte memoryno disk20 Mbyte/sec DMA interface to the file serverEthernet network interface


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CPU Servers

operating system has conventional process model usingforkexec primitives

new processes are run on a new processor whenever possible (similar toAmoeba in this respect)

processors similar to disk blocksbuy more disk space when you run outbuy more processors as well

CPU servers haveno local disk


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File Servers

Plan 9 file server is a modesttwo processor64 Megabyte of memory600 Megabytes of hard disk300 Gigabyte juke box of write-once optical disk (WORM)

it interfaces to the CPU servers through the 20 Mbyte/sec DMA links


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File Servers

file server interfaces to other terminals through conventional networks

file server presents a file system to its clientsnot an array of disk drivesdifferent from Windows in this respect. cfa: b: c: d: e:f:


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File Server (continued)

file system actually resides on WORMthe modest 600 Mbyte driveonlyacts as a cache

RAM

Mbyte

64

worm

Gbyte

300

disk

Mbyte

600

file server

client


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File Server Security and Backup

once a day the file tree is frozen and splitold files can be accessed through normal file operations/1990/0401/usr/rob/doc/plan9.ms

this scheme permits users to compare files against old versions usingtraditional tools applied to a normal file system

permissions are the samesecurity remains intact


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Plan 9 Network Structure

File Server CPU Server

GNOT

20 Mb/s

DMA

Ethernet

DS-1


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GNOT terminal

specialist terminal whose specification is:25 MHz 680201024x1024 4 colour displaykeyboard and mouse4..8 Mbytes of memory2 Mbit/sec packet switched network connects a GNOT to the CPUservers

terminal does not handle compilationmight run a text editor though


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Plan 9 GNOT

cheap enough so that each person can have 21 at work1 at home


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Plan 9 code size statistics

window software written from scratch8 1/2 source is 60K bytes including source for xterm equivalentroughly functionality of X windows (no colour)3860 lines of code and compiles in 10 secondscompare to X windows!

Plan 9 is small!the kernel is 3647 lines of C codeit takes 10 seconds to compile and 10 seconds to load

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