Transcript The Evolution of Operating Systems

Operating Systems and
Networks
Fall 2012
What is an Operating System
• An operating system is a software program
that coordinates activities between the
hardware and the user.
• Unrelated activities should not interfere
with each other and the user should be
unaware of the details involved.
The Evolution of Operating Systems
• Simple means of program execution
– Batch processing
– Job queue
• FIFO fashion (First-In First-Out)
Batch processing
• More complex -- Interactive Processing
– Real-time processing
• Now the machine runs programs in the context of a
user environment,
• the program can be responsive and can be directed
during its execution.
– Crucial to this is time-sharing
• Dividing time into fixed-length intervals, or time
slices. A job is only allowed to execute for a single
time slice, then another is allowed to execute, then
another, …
• This allows the computer to do many things “at the
same time”
Interactive processing
– Time sharing is usually manifest in what we call
multitasking
• Doing many things at once.
• Multitasking can increase efficiency and productivity
• Examples:
– Cooking a meal on a one-burner stove (“serial”) versus cooking a
meal on a 4-burner stove (“parallel”). When you cook on a multiburner stove you are multitasking and assigning time slices to
different items being cooked. Stir one pot for a few seconds, then
turn your attention to another pot and add some ingredients; then
turn to check on a third pot, etc. Each pot is a different process.
– Working on a computer:You finish a term paper and select “print”.
While you are waiting for the paper to print you switch over to
Netscape and surf the web for a while. This would not be possible
without time sharing and multitasking. You would have to wait for
the printer to finish before doing anything else!
Operating System Architecture
• Early on -- operating systems were used to coordinate
and schedule batch processes.
• With multiple users or the need to run different
programs at the same time and handle many different
user interfaces, operating systems became more
complicated and more powerful. Now the operating
system provides an environment in which applications
run.
• Operating system architecture: Let’s start at the top
Software
Application
System
Utility
Operating
Shell
Kernel
• Shell - the interface between the OS and the user
– Modern shells implement a graphical user interface or
GUI (“Gooey”)
– Older shells used a command line interface
• DOS, UNIX
– The shell is merely an interface. Good ones are easy to
use and increase productivity. Poor ones are hard to
figure out, and require wasting time to figure out how
to do something.
• Apple Macintosh, Microsoft Windows, Gnome and KDE on
Linux, Solaris, …
• But this is what the user uses! So it is what most people
associate with computers. The real heart of the computer,
however, is the operating system and the kernel is the heart of
the OS.
The shell as an interface between users and the operating system
The GUI had its roots in the 1950s but was not developed until the
1970s when a group at the Xerox Palo Alto Research Center
(PARC) developed the Alto, a GUI-based computer. The Alto was
the size of a large desk, and Xerox believed it unmarketable.
[Steve] Jobs took a tour of PARC in 1979, and saw the future of
personal computing in the Alto. … When Jobs accused Bill Gates
of Microsoft of stealing the GUI from Apple and using it in
Windows 1.0, Gates fired back:
No, Steve, I think its more like we both have a rich neighbor named
Xerox, and you broke in to steal the TV set, and you found out I'd been there
first, and you said. "Hey that's no fair! I wanted to steal the TV set!
-- www.apple-history.com
• Kernel -- software which performs the most basic
functions required to make a modern computer run
– File manager
•
•
•
•
Coordinates the use of the machine’s mass storage facilities.
Files, directories and folders (hierarchical organization)
path
file descriptor (information needed to find and access a file)
– Device drivers
• Software units that communicate with the controllers of the
devices.
– Memory manager
• Coordinates the machine’s use of main memory (including
virtual memory)
– Scheduler
– Dispatcher
• Booting a computer:
– Boot strapping or booting
• The first thing performed by the computer when it is
turned on (or re-booted)
• The computer is designed so that it’s program counter will
always point to one particular address in ROM. This is
where a permanent program resides which gets the
computer going. It directs the computer to load a
program, or programs, from mass storage (hard disk,
floppy*, CD, …) into main memory and then execute
them. These programs are the operating system binaries.
The booting process
The booting process
Coordinating the Machine’s Activities
• “One of the most fundamental concepts of modern
operating systems is the distinction between a program
and the activity of executing a program.”
– A program -- a static set of directions
– A process -- the dynamic activity of the machine whose
properties change as time progresses. At any particular time
the current status of the activity is called the process state.
– The process state exactly and completely defines everything
needed to run the program. (i.e. the address in the program
counter, the contents of the registers, and the contents of main
memory cells which are being used by the program. It is a
snapshot of the machine at a particular time.
• A program can have many processes associated
with it:
– A word processing program can have many different
files open at the same time. It can also be printing a
document and spell-checking another. These are all
different processes with their own data.
• All these processes (from one program or from
many) compete for processor time (compete for
time slices)
– We must have an administrator to coordinate all this.
• Process Administration
– “Tasks associated with process coordination are
handled by the scheduler and dispatcher within the
operating system’s kernel.”
– Scheduler -- The scheduler maintains a process table
to organize the current processes.
• The process table contains information about each process:
– memory area assigned to the process (from the memory manager)
– priority of the process (ready, waiting, …)
– Dispatcher -- the part of the kernel that ensures that
each scheduled process is actually executed.
• Controls the time-sharing behavior
• Handles interrupts.
Time-sharing between process A and process B
“Paramount to the success of a time-sharing
system is the ability to stop, and later restart,
a process.”
You must be able to pick up exactly where you
left off.
Handling Competition Among Processes
• The OS (here meaning kernel) must be able to
allocate resources of the machine so that all the
processes are executed smoothly, with no errors,
and without time wasting conflicts.
• A potential problem:
– Two processes are competing for resources. One
process holds access to the printer and is waiting for
access to the hard drive. Another process holds access
to the hard drive and is waiting for access to the printer.
Deadlock
Networks
Two broad categories:
• local area networks (LAN’s)
• wide area networks (WAN’s)
– These describe the physical arrangement of the
network
• The operation of the network can be either open or
closed
– Open -- operation is governed by an open standard
of communication. Everyone can see how it works.
– Closed -- proprietary; The details are hidden and are
the exclusive property of a company.
• Classification
–
–
–
–
ring
bus
star
irregular
• The Internet can be understood in terms of collections
of networks called domains. (See figure 3.11)
– Each domain could be a University or a company.
• Each domain is an autonomous system that is
configured and administered by a local authority
(maybe the “Network System Administrator”)
• We must have a common addressing scheme within all
networks so that we can locate a particular machine:
– Each machine is assigned a 32 bit address called an IP
address. Each computer is given a numerical address.
– The IP address is broken down into a host address and a
network identifier.
140.211.117.7 -- gilligan.wou.edu
140.211.117.7
Network identifier
Host address
Addresses go from:
0. 0. 0. 0
to
255.255.255.255
• Thinking about this in a simple way, how many machines
can we put on the internet?
– Total machines
= 232  4.29 billion
– Total domains
= 224  16.8 million
– Machines/domain
= 28  256
• We are accustomed to the alpha-numeric form of
the machine address:
gilligan.wou.edu
• This is not a web address. Rather it contains both
the network identifier and the host address. This is
the machine whose name is gilligan within the
domain wou.edu.
• Domain name: wou.edu
• The domain name is also classified by type:
– .com, .edu, .org, .mil, .gov, .uk, .de, . . .
• E-mail:
[email protected]
locally
assigned
address
for user
Domain
name
• Domain name server
– A directory system that performs conversions from
mnemonic addresses to numeric addresses.
– Responds to requests regarding addresses
– All the Internet’s name servers make up an Internetwide directory system
• New domain?
– Must register with InterNIC
• Internet Service Provider (ISP)
– Companies which establish a domain and then sell
addresses within the domain to users, who usually “dial
in” with a modem. Provides access to the internet and
email.
• Peak, ProAxis, MSN, America Online (AOL), AT&T@Home,
...
• WWW (World Wide Web)
– A world-wide set of documents and files which
can be publicly accessed and are linked
together through hypertext links.
– The web pages we see are written in a hypertext
language. Today the standard is HTML or
Hypertext Markup Language. There are others
and this standard will continue to evolve.
– We access these files with a browser.
• Netscape Navigator, Microsoft Internet Explorer,
Mosaic, Opera, . . .
– Pages are accessed with a unique address called
a uniform resource locator or URL.
• Networks
– Networks operate under protocols.
(communication protocols) This way everyone
is speaking the same language and is abiding by
the same rules.
• Security
– password protection
• NEVER use a birthday, your name, your initials,
common words, etc.
– Encryption
• public-key encryption
– public key -- used to encode messages (can’t decode)
– private key -- used to decode messages
• Monitoring
–
–
–
–
–
FBI
Your employer
This University
Your ISP
Your parents
• Virus
• Worm