Chapter 3 – Operating Systems
Aims:
Identify the main operating system characteristics.
Define typical operating systems.
To classify operating systems.
Define the component parts of an operating system.
Contrast a thread-based approach with processes.
User interface, operating system and hardware
User
Userinterface:
interface:
••Microsoft
MicrosoftWindows
Windows(Windows
(Windows95/98/NT/2000).
95/98/NT/2000).
••Microsoft
Windows
3.1.
Microsoft Windows 3.1.
••X-Windows.
X-Windows.
Operating
Operatingsystem:
system:
••Microsoft
Windows
Microsoft Windows(Windows
(Windows95/98/NT/2000).
95/98/NT/2000).
••DOS.
DOS.
••UNIX/Linux.
UNIX/Linux.
••VMS.
VMS.
••Novell
NovellNetWare.
NetWare.
Hardware:
Hardware:
••x86
x86architecture.
architecture.
••SPARC
SPARCarchitecture.
architecture.
••Apple
architecture.
Apple architecture.
Typical operating systems
DOS. This was one of the first operating systems for the PC, and
quickly become a standard, not because of its technical specifications,
but because of its relative cheapness against the other PC operating
systems.
Microsoft Windows 3.x. This was basically a graphical user interface
(GUI), which used DOS as its operating system, and thus still had all
the major problems of DOS (such as only being able to run 16-bit
software, only being able to access a limited amount of memory, no
networking, and so on).
Microsoft Windows. In the mid-1980s, Microsoft spent a good deal
of time working with IBM on OS/2. Unfortunately the partnership
broke up, and Microsoft used their experience from this project and
fed it into Microsoft NT Version 3.0. This was a radical redesign of an
operating system for the PC. The next version of NT used the
graphical user interface developed with Windows 95. Newer versions
of Windows have included Windows 98, Windows ME and Windows
2000/XP, and each has built on the robustness, networking
infrastructure and GUI of its parents (Windows 95 and NT).
Typical operating systems (cont.)
UNIX. A powerful and robust operating system, which is typically
used in high-powered workstations. It has a kernel, which interfaces to
the hardware. This kernel has the advantage that it can be stripped
away from the GUI and can be run on its own.
Novell NetWare. Around the time of DOS and Microsoft Windows
3.1, there was very little software which allowed computers to be
connected to a network.
VMS. As with UNIX, a powerful and robust operating system. It is
excellent at running batch processes, which are automatically started
when the system is started. They then run quietly with little user input
(typically described as batch processes).
Linux. A version of UNIX for the PC, and one of the few PC-based
operating systems to properly compete with Microsoft Windows.
Operating system components
User account database
Users
Operating system
Groups
Kernel
Kern
Kernaal l
Volumes
File system
Resources
Memory
Printer
Print Queues
Printer Server
Operating system characteristics
Single-user
Multi-user
Stand-alone
Networked
Single-tasking
Multitasking
Single processor
Multi-processor
Operating system classifications
• Single user v. Multi-user. Single-user systems only allow a single
user to login into the system at a time. They have no user account
database, and have a low level of security, as users cannot protect their
files from being viewed, copied or deleted.
• Networked v. Stand-alone. A stand-alone computer does not
connect to a network, and thus cannot access any networked
resources. This obviously creates a more secure environment as
remote users cannot log into the computer.
• Multitasking v. Single-tasking. Multitasking operating systems
allow for one or more programs, or processes, to be run, at a time.
Typically, this is achieved by giving each process a prioritized amount
of time on the processor.
• Multiprocessor v. Single processor. Some operating systems allow
for more than one processor to be used on the system. This allows
more than one task to be run, at a time, on different processors.
Windows server operating systems supports multiprocessors (up to
four processors).
Operating system classifications (cont.)
• Embedded v. Non-embedded. An embedded operating system is
typically integrated into a device, and is used to perform a specific
task, and support for specific applications. Embedded systems are
especially written for certain applications and for a narrow range of
additional hardware.
• Distributed processing v. Localized processing. Most processing
is achieved locally within the computer system (localized processing),
but some processing can be distributed to other computers.
Operating system functions
Memory:
- Creating virtual memory systems
- Disk swapping for memory
Device interfacing:
- Access to connected devices
- Multi - user access
- Device drivers
UNIX
LINUX
Microsoft
Windows
95/98 (OS)
Microsoft
Windows
NT (OS)
Hardware
Mac
OS
Networking:
- Remote login/file transfer
- Creating global file systems
File system:
- Creating a file system
- Copying/deleting/moving files
DOS
Multi-user
- Allowing users to log into the system
- Allowing users permissions to certain resources
- Manag ing queues for resources
Multiprocessing
- Allowing several processes to run, at a time
- Scheduling of processing to allow priority
Operating system functions
File system. All operating systems create and maintain a file system,
where users can create, copy, delete and move files around a
structured file system.
Device interfacing. Operating systems should try and hide the
complexity of interfacing to devices from user programs and the user.
Multi-user. This allows one or more users to log into the system. For
this, the operating system must contain a user account database,
which contains user names, default home directories, user passwords,
user rights, and so on.
Multitasking. This allows for one or more tasks to run on a system,
at a time. Typically this is achieved by giving each task a certain amount
of time on the processor (known as a quanta time slice), and the state
of the task at the end of the quanta is stored to memory, and recalled
when it is next run.
Operating system functions
Multiprocessing. This allows two or more processors to be used, at
a time. When running with more than one processor the operating
system must decide if it can run the processes on the different
processors, or it has to determine if the processes require to be run
sequentially (that is, one at a time).
Multi-threaded applications. Processes are often split into smaller
tasks, named threads. These threads allow for smoother process
operation. Threads of a program use a common area for their data.
They allow smaller processes to run, as larger processes will typically
get stuck waiting for resources to be freed, or data to be inputted.
Multiple access to devices. Some devices allow many programs to
access it, without causing any problems, while others require that only
one program at a time can have access. Memory and disk access allow
multiple access for programs, whereas modems and printers typically
only allow one program to access them at a time.
Operating system functions
Driver loading. A device driver is a special piece of software which
knows how to communicate with a specific device. For example a
mouse driver will know how to receive data from a mouse and then
convert it into a form which can be used by a program. An operating
system is thus responsible for loading device drivers, and making sure
that they act reliably.
Managing memory. This involves allocating memory to processes,
and often involves creating a virtual memory for programs.Virtual
memories were an invention of the VMS operating system, where
programs could be given an almost infinite amount of memory, even
though there was a limited physical memory.
Networking. Typically an operating system must make provision to
create a network either to connect to an external network (such as
the Internet), or in a local network (or domain). This normally involves
loading the required networking protocol, such as TCP/IP for
communications with the Internet.
Pre-emptive or co-operative
• Pre-emptive multitasking. This type of multitasking involves the
operating system controlling how long a process stays on the
processor. This allows for smooth multitasking and is used in 32-bit
Microsoft Windows programs and in the UNIX operating system.
• Co-operative multitasking. This type of multitasking relies on a
process giving up the processor. It is used with Windows 3.x programs
and suffers from processor hogging, where a process can stay on a
processor and the operating system cannot kick it off.
Communication between processes
Process
Process
Data passed between processes
Process
Process
Message or signal
Interrupt
Interrupt
Low-level
Low-level
interrupt
interrupt
Low-level
Low-level
interrupt
interrupt
Network or local computer
Pre-emptive multitasking
Come
Comeon.
on.My
My
turn
soon
turn soon
2
3
Processor
1
Okay
OkayNo.1,
No.1,you’ve
you’ve
had
your
turn,
had your turn,
get
gettotothe
theback
backofof
the
thequeue.
queue.Next!
Next!
4
5
Process queue
Pre-emptive multitasking:
Processes are given some time on the processor.
This allows all the processes to have some time on
the processor, and makes for smoother and more
reliable operation
Co-operative multi-tasking
Hurray.
Hurray.I Icould
could
stay
here
forever.
stay here forever.
Anyway,
Anyway,I’m
I’m
not
going
back
not going backtoto
the
theend
endofofthe
thequeue.
queue.
Hurry
Hurryup.
up.I’m
I’m
waiting.
You’ve
waiting. You’ve
been
beenon
onthat
that
processor
processor
for
forages.
ages.
1
2
Processor
Sorry.
Sorry.You’ll
You’llhave
havetoto
wait
waituntil
untilhe’s
he’s
finished
finished
3
4
Process queue
Co-operative multitasking:
Processes must yield from
the processor, before other processes
can run on the processor
This
Thisisn’t
isn’t
very
fair!
very fair!
5
6
Operating system components
Application
program
Application
program
Communication
with operating system
Operating System
Kernel
Network driver
Keyboard driver
Soundcard driver
Mouse driver
Video driver
Threads in a task
Boil
Boil
potatoes
potatoes
Microwave
Microwave
the
thepie
pie
Pie is
cooked
Potatoes
are soft
Put
Put
pie
pie
on
onplate
plate
Put
Put
potatoes
potatoes
on
onplate
plate
Boil
Boil
carrots
carrots
Carrots
are soft
Put
Put
carrots
carrots
on
onplate
plate
Threads v. processes
Process approach
Threads approach
Interlinking
of threads
Process
Process splits
into threads
Threads
Independent
threads
Common sharing
of data between threads