how operating system works's....

1. adeel_tc@hotmail.com 0315-4632432 1

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3.  process:
• an address space with 1 or more threads
executing within that address space, and the
required system resources for those threads
• a program that is running
 thread:
• a sequence of control within a process
• shares the resources in that process
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4. THREADS
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5.  Advantages:
• the overhead for creating a thread is significantly
less than that for creating a process
• multitasking, i.e., one process serves multiple
clients
• switching between threads requires the OS to do
much less work than switching between
processes
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6.  Drawbacks:
• not as widely available as longer established
features
• writing multithreaded programs require more
careful thought
• more difficult to debug than single threaded
programs
• for single processor machines, creating several
threads in a program may not necessarily produce
an increase in performance (only so many CPU
cycles to be had)
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7. THREADS
 Thread management done by user-level threads library
 Examples
- POSIX Pthreads
- Mach C-threads
- Solaris threads
• Supported by the Kernel
• Examples
- Windows 95/98/NT/2000
- Solaris
- Tru64 UNIX
- BeOS
- Linux
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8. THREADS
 Many-to-One
 One-to-One
 Many-to-Many
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9. THREADS
 Many user-level threads
mapped to single kernel
thread.
 Used on systems that do
not support kernel
threads.
 Examples:
Solaris Green Threads
GNU Portable Threads
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10. THREADS
 Each user-level thread maps to kernel thread.
 Examples
- Windows 95/98/NT/2000
- Linux
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11.  In this model, the library has two
kinds of threads: bound and
unbound
 bound threads are mapped each
to a single lightweight process
 unbound threads may be
mapped to the same LWP
 Probably the best of both worlds
 Used in the Solaris
implementation of Pthreads (and
several other Unix
implementations)
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13. adeel_tc@hotmail.com 0315-4632432