COMP1321 Digital Infrastructure Richard Henson University of Worcester January 2018

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

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

Early Operating Systems Each of the early computers was unique each had to have its own purpose-built operating system IBM: world’s first mass produced “mainframe” IBM 701 (1952) purchasers expected to write their the operating system themselves!

First British Operating system Leo 3…. first mass produced British Computer 94 units built 1961-1969 full list of buyers http://www.leo-computers.org.uk/newleo3s.htm Features: loudspeaker connected to the CPU… so operators could tell if it was “looping” multi-tasking operating system called “master program” Some continued in service until 1981

IBM Leads the world… As well as massive computers, IBM started to produce operating systems first “mass produced” operating system written by General Motors: GM-NAA I/O in 1956 soon adopted by IBM… as IBSYS IBM hugely successful… by 1980s, able to defeat US government in a legal case

First Minicomputer & Operating system Digital Equipment Corporation (DEC), 1963 PDP-6,7,8, etc. “mini” in size compared to mainframes huge by today's standards operating system: “monitor” evolved into the TOPS10 (1970) still going until 1988 can get it even now: http://www.inwap.com/pdp10/96license.txt

Unix Spin-off (1969) from project MULTICS Commercial Challenge: First attempt at a multiuser operating system Consortium including Bell Labs, AT&T, US equivalent of BT at that time FAILED! Too ambitious… Bell Labs: cut down version UNICS -> UNIX written in assembly language by Ken Thompson sharing of processes also being explored by ARPAnet project Commercial Challenge: DEC PDP-7,8, etc. minicomputer needed a general purpose “time sharing” operating system for multiuser use… os “monitor” had not yet matured into TOPS-10

Thompson, Ritchie, “B”, NB, “C” & Unix Thompson looking for a high-level language to develop a time sharing os briefly toyed with Fortran worked with colleague Dennis Ritchie to create their own higher level language – “B”, based on BCPL http://cm.bell-labs.com/cm/cs/who/dmr/kbman.html development of B = newB (NB) development of NB -> C Unix kernel was rewritten in “C” (1973)

Development of Unix/C “C” compiler completed by Ritchie in 1972 Further commercial Unix versions (for Honeywell & IBM) released in 1973 “C” further developed during 1973-7 Full definition of language as Kernighan & Ritchie “C” (1978) rapidly gained universal acclaim Unix still written in “C” to present day! 32-bit processing from the outset

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

Silicon Valley, TCP/IP and Unix University of California: ARPAnet (1969) developed TCP/IP 1980, gained approval through RFC 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… Silicon Valley: IT hot spot around SF developed from 1975…

Bell Labs Unix becomes Commercial… US Dept of Justice broke up AT&T in 1984 Bell Labs then allowed to sell their Unix source code… 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 market operating system provided security on a PC where DOS couldn’t…

Bad days for Unix… 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 Unix became expensive to buy… and was still not user-friendly or easy to use so even more expensive to own!

Linux From 1992 (Linus Torvalds, University of Helsinki) made free Unix possible again! LINUX – based on his name… 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! Still Unix, still a server-end system for client-server networking, need client-end software: e.g. Banyan VINES

Linux Still freely available via Internet! Huge range of software tools for managing UNIX networks available for download 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 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?

Peer-Peer v Client-Server Peer-peer network each computer on the network… needs configuring e.g. to share resources accessed, configured and managed by a single (expert?) user or separate administrator Client-server one (or more) servers in a cluster, managed by experts accessed via “users” on client machines level of user access controlled centrally

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

Networking software and client-server Simple principle… one end of connection = “server” other end = “client” client initiates, server responds… Data transmitted using communication protocol Client Server request response

Peer-Peer and inter-device communication? Not client-server… so how does it work? Answer: communication protocol extended so devices can choose roles one becomes “client”, the other “server”.

Software for “client” and “server” Rather complex… Effectively one program split into two components (processes) data link needed between the two Client-side process Client-server program Excellent communication Server-side process

Network software for Peer-peer Each device needs both client and server processes could assume either role software quite complex all Windows desktop/laptop/tablet machines have this capability Many client processes can in theory link to single server process (!)

Server Operating System Functions (Virtual) Memory, disk, file system, management IP address management Process management Event management Client management User management… etc. etc…

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

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

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

User Authentication Usernames & passwords have to be matched against a database to ensure granting of access is justified Resources made available depending on status (group) of username

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

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

Learning about Networks Only so much can be done in theory Networks have to be used to understand them However, some excellent online simulation resources have been developed Most successful is “Packet Tracer”