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

Inter process communication protection and security 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 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 M.M. IN UNIX Swapping Virtual Memory demand paging 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.

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

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 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.

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 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.

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 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.

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 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.

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

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.

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.