Transcript 11.4 Software Operating Systems

11.4 Software
Operating Systems
FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License
Operating Systems
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All desktop computers use an operating system.
Common desktop operating systems include:
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Windows
OS X
Linux
There are hundreds of other operating systems
available for special-purpose applications e.g.
mobile phones
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Functions of an OS
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Processor management
Memory management
Device management
Storage management
Application interface
User interface
You need to know this for the exam!!!
FatMax 2007. Licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License
Processor Management
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The OS has manage the execution of processes so that you
believe that there are several things happening at once.
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However, the processor can only
do one thing at a time. In order to
give the appearance of lots of
things happening at the same time,
the OS has to switch between
different processes thousands of
times a second making sure that
each process and application
receives enough of the processor's
time to function properly.
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Memory Management
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The OS manages memory (RAM).
When applications are loaded they
need memory to work with. The OS
allocates software RAM to work in. It
ensures that the RAM allocated is
not used by another application.
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The OS also manages virtual
memory. In this way the computer
can run more applications than it has
RAM for. For example if a computer
was running a word processor and
the user wanted to load a
spreadsheet application at the same
time and there was not enough RAM
then the OS uses the hard disc as
virtual RAM.
Click on the image to
watch a short Flash
presentation about
memory management
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Device Management (Input/Output)
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The OS makes use of queues and buffers, special
storage facilities that take a stream of bits (data) from a
device, e.g. a keyboard, hold those bits, and then release
them to the CPU at a rate slow enough for the CPU to
cope with.
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This function is very important when a number of
processes are running and taking up processor time. The
OS will instruct a buffer to continue taking input from the
device, but to stop sending data to the CPU while the
process using the input is suspended. Then, when the
process needing input is made active once again, the OS
will command the buffer to send data.
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Device Management (Drivers)
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The operating system needs to communicate with the
various hardware components which make up the
computer. Special programs called drivers enable the
OS to communicate with these hardware devices. Drivers
are needed as the hardware which makes up a PC may
be vastly different to that of another PC with the same OS
installed.
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Drivers are translation programs which convert the
messages from the OS into messages that the hardware
device can understand.
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Application Interface
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In much the same way that
drivers provide a way for
applications (software) to make
use of hardware without having to
know every detail of the
hardware's operation,
application program interfaces
(APIs) let application
programmers use functions of the
computer and operating system
without having to directly keep
track of all the details in the
CPU's operation.
Think of an API as a set of
common routines,
protocols, and tools for
building software
applications. A good API
makes it easier to
develop a program by
providing all the building
blocks. A programmer
puts the blocks together.
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User Interface
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The user interface (UI) brings structure to the interaction
between a user and the computer.
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In desktop computers the user
interface is a program or set of
programs that sits as a layer
above the OS. The core
operating-system functions the management of the
computer system - lie in the
kernel of the operating system.
The display manager is
separate, though it may be tied
tightly to the kernel beneath.
Mac OS X GUI
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Exam Stuff
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A common question on the exam is:
• “Explain four tasks that an operating system
carries out in the background”
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Can you answer this question?
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