OPERATING SYSTEMS

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OPERATING SYSTEMS

• Introduction
• Lots of choices in operating systems. (ex.)unix,
  windows, chorus, Mac, etc
• Lots of factors in deciding an operating system
• They are
• Design architecture
• Programmer interface
• User interface
• Process management
• Memory management
• File system
• I/O system

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• Inter process communication
• protection and security
• In todays world there are lots and lots of OS
  around.
• We will discuss these features of two prominent
  OS UNIX and WINNT.

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Design architecture

• DESIGN OF UNIX
• Consists of mainly three parts viz.
• 1. Tools and applications
• 2. Shell
•      connects and interprets users command,
  call programs from memory and executes them.
• 3. Kernel
• Manages all hardware devices and view each of
  them as a file

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MEMORY MANAGEMENT

• M.M. IN UNIX
• The Unix kernel divides the memory in to
  manageable chunks called Pages.A single page of
  memory is usually 4096 or 8192 bytes( 4or 8 kb
  ).Memory pages are laid down contiguously across
  the physical and virtual memory.
• Swapping
• Process are moved in and out of main memory.
  The First Fit algorithm is used.
• Virtual Memory demand paging
• Pages are created only for the process that
  actually execute. When a process access an
  address that is not part of working set(set of
  pages in main memory) page fault occurs.

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• DESIGN OF WINNT
• The four major pieces of the NT architecture
  follow
• 1. Hardware Abstraction Layer (HAL)
• Software interface between the
  hardware and the rest of the operating system
• 2. Kernel (Micro kernel)
• Ultimately responsible for all actions on the
  system and almost all functions on the system
  pass through it.
• 3.NT Executive Services
• NT Executive takes care of the important tasks
  that are vital to the entire system, but the
  kernel is too busy to address directly. Some of
  them are OM, PM, VMM, LOCAL PROCEDURE CALL
  FACILITY, I/O MANAGER

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• M.M IN WINNT
• Virtual Memory Manager (VMM) provides management
  of the system's virtual memory pool.
• Each process is allocated a 4GB virtual memory
  space. Of this space, the upper two gigabytes is
  reserved for system use, while the lower 2GB is
  for the process's use
• If the process's memory address refers to a piece
  of memory that has been paged to disk, the VMM
  retrieves the page from disk.

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PROCESS MANAGEMENT

• PROCESS MANAGEMENT IN UNIX
• Each process has two stacks a User stack and a
  Kernel stack. At least two different modes of
  operation are used by the Unix the more
  privileged kernel mode or less privileged User
  mode.
• Kernel mode
• Process carrying out Kernel instructions is
  said to be running in the Kernel mode. While in
  the kernel mode the process may access the data
  and code of any process.
• User mode
• Process, created directly by the users and
  running on the CPU are said to be in User mode.
  The process doesnt have the privileges of the
  kernel mode that is they can access the data of
  other processes.

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• PROCESS MANAGEMENT IN WINNT
• When the application starts a process is created
  by process manager.
• The process manager is responsible for creating,
  removing and modifying all the processes and
  threads created in the system.
• It provides information about the status of the
  processes and the threads to the rest of the
  system.
• This is a main part of the windows NT executive.

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FILE SYSTEM

• FILE SYSTEM IN UNIX
• Everything in Unix are viewed as files.
• Three types of files
• 1. Regular files holds executable programs
  and data
• 2. Directory files - contain other files and
  subdirectories. Helps to organize other files.
• 3. Device files Unix treats even the hardware
  such as printers, CD-ROMs, Modems as a file.
• Kernel uses a logical device number, node number
  pair to identify a file in the system.

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• FILE SYSTEMS IN WINNT
• Windows NT has an advanced version of FAT (File
  Allocation Table) file system, NTFS (NT File
  system) and HPFS (High Performance File system).
• A major part of the security model that NT offers
  is based on the NTFS file system.
• A HPFS can be converted to a NTFS using
  convert.exe utility.
• File descriptions on an NTFS volume are stored in
  a master file table (MFT), which is also a file.
• With many copies of MFT file recovery is easier.

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I/O SYSTEMS

• I/O SYSTEMS IN UNIX
• The I/O system hides the kernel from the
  complications of I/O devices.
• I/O consists of
• 1. Buffer caching system
• 2. General device driver code and drivers for
  specific device drivers.
• Use descriptors to refer I/O streams.

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• I/O SYSTEM IN WINNT
• Specific I/O manager present.
• Responsible for coordinating and processing all
  inputs and outputs of the system.
• It oversees the device drivers, installable file
  systems, network redirectors and the system
  cache.
• It presents a layered approach to mix and match
  various input and output devices.

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INTER-PROCESS COMMUNICATION

• INTER-PROCESS COMMUNICATION IN UNIX
• Several ways by which processes can communicate.
  Some of them are
• 1. Pipes - reliable unidirectional byte stream
  between two processes.
• 2. Semaphores and shared memory
• 3. Message queues
• 4. Sockets Two way communication pipe.
  Communication can be done in both the ways using
  sockets.

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• INTER-PROCESS COMMUNICATION IN WINNT
• Here also there are different ways for
  inter-process communication. Some of them are
• 1. WINSOCK
• 2. RPC
• 3. DDE
• 4. NETBIOS
• 5. NAMEDBIOS
• 6. SEMAPHORES
• 7. MEM- MAPPED FILE

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Protection and security

• PROTECTION AND SECURITY IN UNIX
• Unix is basically written in C.
• Security is implemented using various software.
• Some of the network security tools in Unix are
• 1. IPACL
• 2. LOGDAEMON
• 3. PORT MAP
• 4. RPCBIND, SARA ETC.
• Various companies market these tools.

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• PROTECTION AND SECURITY IN WINNT
• Some of the security features are
• 1. Logon characteristics
• 2. Mandatory logon
• 3. Auditing
• 4. Limited network access
• The security features are controlled by security
  reference monitor NT executive.