Transcript OPERATING SYSTEMS

OPERATING SYSTEMS
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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
Inter process communication
protection and security
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In today’s world there are lots and lots of OS
around.
We will discuss these features of two prominent
OS UNIX and WINNT.
Design architecture
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DESIGN OF UNIX
Consists of mainly three parts viz.
1. Tools and applications
2. Shell
connects and interprets user’s
command, call programs from memory and
executes them.
3. Kernel
Manages all hardware devices and view
each of them as a file
MEMORY MANAGEMENT
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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.
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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.
PROCESS MANAGEMENT
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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 doesn’t
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.
FILE SYSTEM
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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.
I/O SYSTEMS
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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.
INTER-PROCESS
COMMUNICATION
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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 interprocess communication. Some of them are
1. WINSOCK
2. RPC
3. DDE
4. NETBIOS
5. NAMEDBIOS
6. SEMAPHORES
7. MEM- MAPPED FILE
Protection and security
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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.