Wednesday, June 07, 2006

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Wednesday, June 07, 2006

• Unix is user friendly
• its just picky about its friends.
• - Anonymous

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CS 381 Operating Systems

• Course URL
• http//suraj.lums.edu.pk/cs381m05
• Folder on indus
• \\indus\Common\cs381m05
• Read course policies on the website!

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• Some design issues
• I/O Space
• Special IN/OUT instructions (use of assembly
  code)
• Calling procedure adds overhead to I/O
• Memory mapped
• Con
• Uses up some memory space
• Caching of device registers should not be done!
• Multiple buses
• Pro
• No extra protection needed to keep user processes
  from doing I/O

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• Unix
• Initial project turned into multimillion dollar
  industry involving universities, government
  organizations, multinational corporations.
• Late 1980s
• ATT (System V) and UC, Berkeley, (BSD)
  incompatible versions
• IEEE standard for UNIX
• POSIX (defines minimal system call interface)

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• Unix
• A multi-user, time-sharing operating system.
• It can have many users logged into a system
  simultaneously, each running many programs.

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• Unix
• Command based interface
• Al most all UNIX systems support a windowing
  system as well
• X-Windows
• Developed at MIT

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• Linux
• Underlying structure common to UNIX
• Versions subsequent to MS-DOS included many
  advanced features taken from UNIX.
• Our discussion shall apply to different
  versions/clones of UNIX like BSD, System V, Linux
  etc. (Sun Solaris has its own variant of UNIX).

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• Linux
• Linux availability across a wide spectrum of
  platforms
• Distributions implemented on 64-bit architecture
  processors.
• Large enterprise servers
• Medium sized and small servers, workstations
• Desktops
• Laptops
• Small intelligent devices.

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• IBM Linux-based wrist watch.

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• Mainframe Operating Systems
• Major organizations
• Huge I/O capacity
• Batch
• Processes not requiring user interaction
• (payroll processing, sales reporting )
• Transaction Processing
• Small requests e.g. bank system, airline systems
• Time Sharing
• large number of remote users
• Example OS/390

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• Server Operating Systems
• Major organizations
• High end web-servers, commerce sites, file
  service etc.
• UNIX, Windows Server, LINUX

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• Speechome Project, MIT
• Massive petabyte (one million gigabyte) disk
  storage system at the Media Lab at MIT

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• Multiprocessor Operating Systems
• Real Time Operating Systems
• Embedded Operating Systems
• Simple OS One program, one user, one machine
• Examples embedded controllers such as nintendo,
  cars, elevators, cellphones

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Ways to do I/O

• Programmed I/O
• User program makes a system call
• That is translated into a procedure call for the
  relevant device driver
• Device driver starts I/O and keeps polling the
  device to see if it is done (device busy status
  check).
• When device is done it puts the data where
  needed.
• OS returns control to user program

Disadvantage?
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Ways to do I/O

• Programmed I/O
• Con
• Busy waiting
• Tying up CPU until I/O is done
• Busy waiting is inefficient

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Ways to do I/O

• Programmed I/O
• Con
• Busy waiting
• Tying up CPU until I/O is done
• Busy waiting is inefficient
• Pro
• Easy to implement
• Embedded systems

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Ways to do I/O

• Interrupt Driven I/O
• Driver starts the device and asks it to give it
  an interrupt when it is done.

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• Interrupt Driven I/O

• For example Read from Disk
• Interrupt signal causes the CPU to stop what it
  is doing and use the interrupt number to start a
  interrupt service handler
• When the handler is done control is returned to
  previously running user program
• Information of interrupted program is saved
  before hand.

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Ways to do I/O

• Direct Memory Access (DMA)

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BIOS

• BIOS (Basic Input Output System) is a program
  that resides on the motherboard.
• Can read from keyboard, write to disk, write to
  screen etc.

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BIOS

• Checks how much memory is installed, keyboard etc
  installed or not.
• Scans buses and detects devices.
• Determines boot device from the list stored in
  CMOS memory.

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BIOS

• First sector from boot device is read into memory
  and executed.
• This gives information about which partition is
  active.
• From there a boot loader is read which loads the
  OS
• The OS queries the BIOS to get configuration
  information and checks if each device has a
  device driver
• One all device drivers founds loads them in
  kernel starts login program.

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BIOS

• First sector from boot device is read into memory
  and executed.
• This gives information about which partition is
  active.
• From there a boot loader is read which loads the
  OS
• The OS queries the BIOS to get configuration
  information and checks if each device has a
  device driver
• One all device drivers founds loads them in
  kernel starts login program.

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Memory
On chip cache
Optical disks, EEPROM, flash RAM
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