COMP1321 Digital Infrastructure Richard Henson University of Worcester February 2013

Week 12: Network Operating Systems n n Explain how client-server and peer-peer systems communicate and function n n Explain the dual role of any operating system n n Explain the various essential roles of specialised software in a network operating system

Functions of an Operating System n n Coordinate hardware so it all works together cooperatively n n Provide a means for human input into the system that can control the hardware components

Early Operating Systems n Each of the early computers was unique  each had to have its own purpose-built operating system n IBM: world’s first mass produced “mainframe”  IBM 701 (1952) »purchasers expected to write their the operating system themselves! »first “mass produced” operating system written by General Motors: GM-NAA I/O in 1956 n adopted by IBM as IBSYS  IBM hugely successful; by 1980s, allegedly bigger than US government (?)

First British Operating system n Leo 3 was the first mass produced British Computer  94 units built »full list of buyers computers.org.uk/newleo3s.htm computers.org.uk/newleo3s.htmhttp:// computers.org.uk/newleo3s.htm  each had a loudspeaker connected to the CPU… so operators could tell if it was “looping”  had a multi-tasking operating system called “master program” n Some continued in service until 1981

First Minicomputer & Operating system n Produced by Digital Equipment Corporation (DEC) in 1963  called the PDP-6 »“mini” in size compared to mainframes »huge by today's standards  operating system called “monitor” »evolved into the TOPS10 (1970) »ran on the legendary PDP-10 »still going until 1988 »can get it even now: »

Unix n Spin-off (1969) from project MULTICS  First attempt at a multiuser operating system »Consortium including Bell Labs, AT&T, n US equivalent of BT at that time »FAILED! Too ambitious…  Bell Labs: cut down derivation called UNICS -> UNIX »written in assembly language by Ken Thompson »sharing of processes also being explored in The ARPAnet project n Commercial Challenge: DEC PDP-7 minicomputerDEC PDP-7 minicomputer »needed a general purpose “time sharing” operating system for multiuser use… »their own os “monitor” had not yet matured into TOPS-10

Thompson, Ritchie, “B”, NB, “C” & Unix n Thompson looking for a high-level language to develop a time sharing os briefly toyed with Fortranbriefly toyed with Fortran worked with colleague Dennis Ritchie to create their own higher level language – “B”, based on BCPLworked with colleague Dennis Ritchie to create their own higher level language – “B”, based on BCPL » development of B = newB (NB)development of B = newB (NB) development of NB -> Cdevelopment of NB -> C Unix kernel was rewritten in “C” (1973)Unix kernel was rewritten in “C” (1973)

Development of Unix/C n “C” compiler completed by Ritchie in 1972 n Further commercial Unix versions (for Honeywell & IBM) released in 1973 n “C” further developed during n Full definition of language as Kernighan & Ritchie “C” (1978)  rapidly gained universal acclaim n Unix still written in “C” to present day!  32-bit processing from the outset

Open Sourceness of Unix n AT&T not allowed to be a commercial company could not sell Unixcould not sell Unix gave a copy away free to any developer who wanted to use it!gave a copy away free to any developer who wanted to use it! many universities contributed to its developmentmany universities contributed to its development n Result (in 1979): Unix version 7 still recognisable today!still recognisable today!

Silicon Valley, TCP/IP and Unix n University of California created The ARPAnet (1969) n 1975 onwards: Berkeley, north of San Francisco hub for its own unique brand of Unix developmentshub for its own unique brand of Unix developments start of “Silicon Valley” (IT hot spot around SF)start of “Silicon Valley” (IT hot spot around SF) n ARPAnet team developed TCP/IPdeveloped TCP/IP 1980, gained approval through RFC1980, gained approval through RFC operating system that would support TCP/IP arrived in 1983…operating system that would support TCP/IP arrived in 1983… »Berkeley Unix (v4.2) packaged with TCP/IP protocol stack »Sun Microsystems producing the hardware…

Bell Labs Unix becomes Commercial… n US Dept of Justice broke up AT&T in 1984 Bell Labs then allowed to sell their Unix source code…Bell Labs then allowed to sell their Unix source code… n Fortunately for SCO (Santa Cruz Operations) they had ported Bell Unix to Intel hardware the previous year (!) SCO Unix for PC became a lucrative business marketSCO Unix for PC became a lucrative business market operating system provided security on a PC where DOS couldn’t…operating system provided security on a PC where DOS couldn’t…

Bad days for Unix… n Unix free by nature from outset  not so on an Intel PC, thanks to SCO!!!  Bell Labs jealously guarded the source code…  universities lost interest n Unix became expensive to buy… and was still not user-friendly or easy to use so even more expensive to own!

Linux n From 1992 (Linus Torvalds, University of Helsinki) made free Unix possible again!  LINUX – based on his name… n Took…  Stallman’s GNU open source Unix »which Tanenbaum had developed into MINIX…  very stable  secure file system  very efficient, optimised code  earlier versions ran on an Intel 486! n Still Unix, still a server-end system  for client-server networking, need client-end software: »e.g. Banyan VINES

Linux n Still freely available via Internet! n Huge range of software tools for managing UNIX networks available for download n Problems (compared to Windows):  not as easy to manage  limited on-screen help  limited range of good application software  not all hardware has UNIX/LINUX driver software

Group exercise n Consider something that you’d like computer to do for you….  What do you want to happen?  Which hardware must do what to make that a reality?

Specialised Functions of a Network Operating System n Support for communication protocols and e.g. the TCP/IP stack n n All of the centralised tasks needed to keep the network running normally n n All achieved through software: n n highly optimised n n executes code as quickly as possible…

Memory Management n Based on good use of addressing n All programs and their data stored within fixed memory location blocks n Need to ensure that there is no memory “creep”

Virtual Memory Management n Extra space on hard disk n Data constantly being swapped between main memory and virtual memory to maximise performance

Disk Management n Ensure data accessed from and directed to right addresses n Partitioning and formatting new disks and areas of disk n Using mirroring, duplexing and RAID as appropriate to maximise disk performance

File Management n Choice of filing system when formatting  FAT?  FAT32?  NTFS  Others?

IP address Management n Most networks now use IP addresses n System needed to manage IP addresses across the network… n Dynamic Host Configuration Protocol n Managed as client-server

User and Group Management n New users have to be defined n Users have to be allocated to groups n Group have to be defined so as to allow appropriate access so people can do their jobs efficiently

User Authentication n Usernames & passwords have to be matched against a database to ensure granting of access is justified

Store of Network Information n Computer names and addresses n Device names n Group and User names n Service names…

Transferring Data efficiently to another Device n Some will get corrupted en route… n Error(s) need to be detected n Request then follows to resend the data n Part of communication protocol