1. COMP1321 Digital Infrastructure
Richard Henson
University of Worcester
January 2018

2. 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

3. 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

4. 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!

5. First British Operating system
Leo 3…. first mass produced British Computer
94 units built
full list of buyers
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

6. 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

7. 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:

8. 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

9. 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
development of B = newB (NB)
development of NB -> C
Unix kernel was rewritten in “C” (1973)

10. 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
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

11. 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!

12. 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…

13. 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…

14. 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!

15. 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

16. 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

17. 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?

18. 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

19. 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…

20. 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

21. 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”.

22. 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

23. 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 (!)

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

25. 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”

26. 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

27. 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

28. 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

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

30. 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

31. 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”