Operating Systems

1
Operating Systems

• Tian-Li Yu
• tianliyu_at_cc.ee.ntu.edu.tw
• Department of Electrical Engineering
• National Taiwan University

2
Batch processing

• Computer operators
• FIFO

Textbook, Figure 3.1
3
Interactive processing

• OS with remote terminals

Textbook, Figure 3.2
4
History of OS

• Batch
• Interactive
• Real-time
• Response time is critical
• Time-sharing and multitasking
• Dividing time into intervals
• Only one task is being performed at any given
  time
• Multiprocessor
• Load balancing
• Scaling

5
Software classification
Textbook, Figure 3.3
6
Linux world

• http//www.linux.org
• Freeware
• Open-source
• Distro (http//distrowatch.com/)
• Personal favorite Gentoo (http//www.gentoo.org/)
  
• In fact, Linux means only the kernel
• Better to call the OS GNU/Linux?
• Servers, PCs, embedded systems.

7
Shells

• Communication with users
• Text based
• GUI (graphics user interface)

8
Kernel

• File manager
• Directory/folder, path
• Device drivers
• Memory manager
• Allocating main memory
• Paging, virtual memory
• Scheduler
• Dispatcher
• Can you recognize these shell and kernel
  components on your PC?

9
Lets turn on a computer

• Boot strapping (booting)
• BIOS (basic input/output system)

Textbook, Figure 3.5
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Process

• Process
• Process state
• Program counter
• General purpose registers
• Associated memory cells
• Process table
• Memory area assigned to the process
• Priority
• Ready/waiting

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Process administration

• Scheduler
• Decide which process should be in the process
  table
• Adds new processes
• Removes completed processes
• Dispatcher
• Controls the allocation of time slices to the
  processes in the process table.
• Interrupt
• Process switch/context switch

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Time-sharing between 2 processes
Textbook, Figure 3.6
13
Semaphores

• A visual signaling apparatus with flags, lights,
  or mechanically moving arms, as one used on a
  railroad. (www.dictionary.com)
• Test-and-set
• Critical region
• Mutual exclusion

Operating system concepts Silberschatz Galvin,
1995 Addison-Wedley
14
Prerequisites for deadlock

• Competition for non-shareable resources.
• Resources are requested on a partial basis that
  is, having received some resources, a process
  will return later to request more.
• Once a resource has been allocated it cannot be
  forcibly retrieved.

15
Deadlock vs. Starving
A
B
C
Processes
1
2
3
4
Resources
16
Security

• Insecure password
• Sniffing software
• Virus/worms/Trojan horses
• Privilege levels
• Privileged instructions

17
Exercises

• Ch 3.3 1, 2
• Ch 3.4 1
• Ch 3 3, 13, 18, 19, 30, 34, 36, 40, 42