UNIX & Windows NT

Name: Jing Bai

ID: 90297

Date:8/28/00

Content

1. Introduction

2. Kernel Architecture

3. File System

4. Memory Management

5. Security

6. Conclusion

IntroductionUNIX:

•It is a machine independent operating system. Ken Thompson developed it in 1969

• Unix OS was written by programmer to programmer. It use C language to instead of the previously used assembly language

•Time-sharing, multi-user, multi-tasking are basic designed in the system(Multiple users can have multiple tasks running at same time)

Windows NT

• Microsoft released it in 1993. It was a full 32-bit OS

• Its design goals include extensibility, portability, reliability, compatibility, performance and international support.

Unix Kernel model

Figure 1

System call interface

File subsystemProcess management subsystem

inter-process communicationprocess scheduling

Disk block cache

Character I/O Block I/O

Hardware

Unixshell

us

User program

library

Unix command program

library

Use level

Kernel level

Memory management

Derive drivers

Hardware control-interrupt service Kernel level

Hardware level

Swapper process 0

Int process 1

=Process

Windows NT kernel mode

Figure 2

Win 16 application

Logon process

O/S application

Win 32 application

MSDOD application

POSIXapplication

Securitysubsystem

Authentication package

Security-account-manage database

O/Ssystem

Win 16VDM

MSDOSVDM

POSIXsystem

Win 32subsystem

Kernel

Hardware abstraction Layer

Hardware

I/O manager

User mode

Object

manager

Security-reference-monitor

Process

manager

Virtual-memory-manager

Local procedure call facility

Kernel mode

Executive

Device drivers

network

drive

File system

cache manager

UNIX File System

• UNIX file is a Hierarchical file structure. All the files are organized into a multi-leveled hierarchy called a directory tree

•The file system supports two main objects: file and directory

• The directory contains a root directory with many subdirectories

• File is stored as an array of fixed-size data blocks with perhaps a fragment

• The block sizes are set during a file system creation

Directory files atinterior node

/

A B

d1 d2

dev

AB

f1

AA

a2a1 a3

The root directory

Normal files at the leaves

Special files in the device directory/dev

Other directoriesand file

UNIX File System Interface

UNIX File System Implementation

• IN Unix system, a file is represented by an Inode (Index Node)

• An Inode is a record that stores most of the information about a file on the disk, such as its size and location. Each file has an own indoe, all inodes have the same size

• The inode contains pointer that points to file block. In Unix, the first 12 pointers of inode point to blocks directly, so small files can be accessed efficiently.

• Example for READ file

UNIX mapping of a file descriptor to an Inode

User space System space Disk space

Read(4...)

Tables of open files

File-structure table

In-core inode list

Inode

list

Data

blocks

UNIX Memory Management• UNIX system uses swapping to handle memory contention among processes. Processes are swapped out until enough memory is available. The process is either in the memory or on the disk.

• Decisions regarding which processes to swap in or out are made by the scheduler process. The scheduler wakes up at least once every 4 seconds to check for processes to be swapped in or out

• A process is more likely to be swapped out if it is idle, has been in main memory a long time or it is large

• A process is more likely to be swapped in if it has been swapped out a long time, or is small

Unix Memory Management

• Berkeley introduced paging to UNIX. Paging is added in order to handle a large programs . The basic idea is : some programs don’t need entirety bring into memory to run. Such as text, data. We can bring them to memory by dynamic. When we need them, we can bring in.

• Paging can eliminate the external fragmentation of memory. Page-replacement algorithm can keep enough free frames to support the executing processes.

Window NT File System

• The fundament entity in NTFS is a volume. A volume is created by the NT disk administrator utility, and is based on a logical disk partition. The volume may occupy a portion of a disk, may occupy an entire disk, or may span across several disks. In NTFS, all information about the volume are stored in a regular file.

• NTFS does not deal with individual sectors of a disk, but instead uses clusters as the unit of disk allocation. A cluster is a number of disk sectors that is a power of 2. The cluster size is configured when an NTFS file system is formatted.

Window NT File System

• A file in NTFS is a structured object consisting of attributes. Each attribute of a file is an independent byte stream that can be created, deleted, read, and written.

• Every file in NTFS is described by one or more records in an array stored in a special file called the master file table (MFT). The size of a record is determined when the file system is created.

Windows NT Memory Management

• The virtual-memory portion of the NT executive is the virtual-memory manager(VM)

• The VM manager in NT uses a page-based management scheme with a page size of 4KB. Pages of data that are assigned to a process but are not in physical memory are stored in the paging file on disk

• The VM manager uses 32 bit addresses, so each process has a 4 GB virtual address space. The upper 2GB is identical for all processes, and is used by NT in kernel mode. The low 2 GB is distinct for every process, and is accessible by both user-and kernel mode threads

Windows NT Memory Management

• The NT VM manager uses a two-step process to allocate memory. The first step reserves a portion of the process’s address space. The second step commits the allocation by assigning space in the NT paging file.

• The VM manager allows a privileged process to lock selected pages in physical memory thus ensuring that the pages will not be swapped out to the paging file

FILE SYSTEM

UNIX• Hierarchical file

structure• File and Directory• Block• Inode

WINDOWs NT• NTFS• Volume• Clusters• MFT(master file table)

Memory Management

UNIX• Swapping • Paging

WINDOWs NT

• Virtual-memory manager(VM)

• Paging File

Conclusion

UNIX• Mature and cheaper

• Reliability

• Configuration do not require a shutdown and reboot

• Can setting keyboard and mouse

NT• Immature And Expensive

• Set up e-mail by separate software

• Slow

• More crash than UNIX

• Less stability than UNIX