Transcript Computer Software

Operating Systems
Categories of Software
• System Software
– Operating Systems (OS)
– Language Translators
– Utility Programs
• Application Software
Operating Systems
• It is the job of the operating system to
manage the computers resources and control
the execution of programs.
• Computer resources include
– memory
– device drivers for peripheral devices
• The OS is the interface between the
hardware and the user/application program.
Layers of interaction
Users
Application Software
System Software
Hardware
OS Evolution
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Computer Operators, No OS
Basic OS
Multi-program
Task switching
Multi-tasking
Preemptive Multi-tasking
Computer Operators, No OS
• Programs were load and run by the
Computer Operator.
• Computer operator
– Specified the memory locations to load a
program and data
– Specified the starting memory location for a
program
– Pressed the run button to run the program
Basic OS
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User manually started programs
The OS handled the memory management.
The OS handled disk management
e.g. DOS = Disk Operating System
Multi-Program
• Multiple programs were loaded into
memory at the same time.
• Only one program could run at any given
time.
• User would manually switch between
program.
• e.g. Mac System 1(a GUI interface)
Task Switching
• Allow the OS to switch between programs
• Each program needed to run to completion
or be halted by the user before the OS
would switch to the next program.
• Keep in mind that the CPU could only run
one program at any given time.
Multi-tasking
• Gives the illusion that multiple programs are
running at one time.
• A second is divided up into time slices (e.g. a
millisecond) and each program is allowed to
run for a time slice in a round robin fashion.
• If two program took 5 minutes each to run
they would now both complete in 10 minutes.
Process & I/O bound
• It was observed that a running program may
be in one of two states:
– Processor (CPU) bound
• Program is running as fast as the CPU can execute
its commands
– I/O bound
• Program is waiting for input from a device, or
• Program is waiting to output to a device, or
• Program is waiting for an event to occur
Preemptive Multi-tasking
• Rather than giving each program its time
slice the OS looks at the program state.
– If program ready to run it gets it slice.
– If program is not ready it is skipped.
• Since many programs spend most of their
time an I/O bound state throughput can be
significantly increased.
Common Operating Systems
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CP/M
DOS
Windows 3.1
Windows 95
Windows NT
Windows Vista
Windows 7, 8, 10
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OS/2
System 7, 8, 9
Mac OSX
Linux
UNIX
VMS
VM/CMS
More CPU / RAM / HDD
OS
CPU
RAM
HDD
DOS 6.22
4 KHz
512 KB
5 MB
Windows 3.0
12 KHz
3 MB
14 MB
Windows 95
12 KHZ
4 MB
35 MB
Windows 98
66 MHz
16MB
205 MB
Windows ME
150 MHz
32 MB
480 MB
Windows XP
233 MHz
64 MB
1.5 GB
1 GB / 2 GB
16 GB / 20 GB
32-bit/64-bit
32-bit/64-bit
Windows Vista, 7,8,10 1 GHz
http://www.osfiles.com/index.htm