hello dears

 i want make presentaion in Operating System Design . exactly (i want summarise chapter 3 and 4 in new presentation)

 

 

It is a term used to describe how the OS handles the
available RAM. It is managed at multiple levels. The most basic level
Its size is the sum of all the capacities of all RAM. For example, when you have two 512 MB SDRAM*
modules installed in your system, the OS will have 1
GiB of physical memory at its disposal. *512 Megabytes Synchronous Dynamic RAM If someone asks you how much memory your computer has,
they're not talking about hard drive space. They're asking you how much RAM your computer has. Just as with your computer, when you want to write a
letter or work on some project, you need to open
programs and spread them out within your computer's
memory—it's RAM. If you have a simple note to write, you might use a little
program like Notepad. If it's a more involved project, maybe you'll open Word
or some special stationary program. The bigger the program, the more RAM will be
needed and subsequently used. If you have a large dining room table, just like a lot of
RAM, you'll find you don't have much difficulty getting
the job done because you have lots of room on that
table to work. Just as your computer has lots of RAM to allow
programs to work quickly. An imaginary memory area supported by some OS in
conjunction with the hardware. You can think of virtual memory as an alternate set of
memory addresses. Programs use these virtual addresses rather than real
addresses to store instructions and data. The purpose of virtual memory is to enlarge the
address space, the set of addresses a program can
utilize. On top of the physical memory is the segmented memory.
is one of the most common ways to achieve memory protection An address space logically divided into sections,
called segments. Address space Memory allocated to an application by the operating system.
Logically related A segment has a set of permissions, and a length,
associated with it. If the currently running process is allowed by the
permissions to make the type of reference to memory
that it is attempting to make, the reference is
permitted. Segmented Memory is the additional 64 KB of RAM
for early computers. But most operating systems today don't use a
segmented memory model, with the advent of
paging. A technique used by virtual memory operating systems to help
ensure that the data you need is available as quickly as possible. the OS retrieves data from secondary storage in samesize blocks called pages. The operating system copies a certain number of
pages from your storage device to main memory. When a program needs a page that is not in main
memory, the operating system copies the required
page into memory and copies another page back to
the disk. When a program needs a page that is not in main
memory, the operating system copies the required
page into memory and copies another page back to
the disk. To replace pages or segments of data in memory. Swapping is a useful technique that enables a
computer to execute programs and manipulate data
files larger than main memory. The operating system copies as much data as possible
into main memory, and leaves the rest on the disk. When the operating system needs data from the disk,
it exchanges a portion of data (called a page or
segment ) in main memory with a portion of data on
the disk. Swapping is when an
entire process is
swapped out. Paging refers to making
individual pages of
memory. Paging is normal. Swapping happens
when the resource load
is heavy and the entire
process is written out
to disk. With paging, memory is managed in 4 KB-sized chunks.
Most applications require the ability to be able to get
only a fraction of that size, to store data. The memory allocator gets a big chunk of memory For example
4 pages, or 4 * 4 KB = 16 KB
and divides this into much smaller chunks which it
gives to the applications when requested. In programming, an area of memory reserved for data that is
created at runtime. an area of memory reserved for data when the
program actually executes. an area of memory reserved for data whose size can
be determined when the program is compiled. begins by building
a heap out of the data
set, and then removing the
largest item and placing it at
the end of the sorted array. After removing the largest item, it
reconstructs the heap and
removes the largest remaining
item and places it in the next
open position from the end of the
sorted array. This is repeated until
there are no items left in the heap
and the sorted array is full. To divide memory or mass storage into isolated sections. In addition, partitioning on Windows machines can
improve disk efficiency. Buffer A temporary storage area, usually in RAM. For example, word processors employ a buffer to keep
track of changes to files. Then when you save the file, the word processor
updates the disk file with the contents of the buffer. This is much more efficient than accessing the file on
the disk each time you make a change to the file. Another common use of buffers is for printing
documents. When you enter a PRINT command, the operating
system copies your document to a print buffer (a free
area in memory or on a disk) from which the printer
can draw characters at its own pace. This frees the computer to perform other tasks while
the printer is running in the background. Print
buffering is called spooling. Most keyboard drivers also contain a buffer so that
you can edit typing mistakes before sending your
command to a program.

 

FILE SYSTEMS File Systems File organization
Access methods
Directory Organization: single, twolevel, hierarchy
File system and directory
implementation
Allocation schemes : contiguous, linked,
indexed File system
In a computer, a file system (sometimes written
filesystem) is the way in which files are named and
where they are placed logically for storage and
retrieval.
The logical unit within a file system is the file logical files are mapped into physical entities by the
OS in user's view, file is the smallest unit that can be
saved to disk A file system defines the structure and the rules
used to read, write, and maintain information
stored on a disk.
Which system used is determined by; Hardware Software Security needs Need for a dual-booting system File Attributes name : provides handle for reference
• DOS (8 chars + 3 char extension), Windows
(unlimited? length)
• UNIX (spaces tricky, no extension needed) type : indicates how the file should be treated
• DOS/Windows rely on extension, can map extensions
to programs
• Mac associates creator attribute with each file (OS X?)
• UNIX uses "magic number", first few bytes of file
specify file type protection : permissions, access control
information
• UNIX utilizes permission string: chmod 644
foo.txt -rw-r--r—
owner & group: chown, chgrp
• Windows utilizes file properties/attributes:
NoAccess, List, Read, Read & Add, …
Location & Size
Accounting Information e.g. MS-DOS filename Filename: 1 to 8 characters
File extension: 1 to 3 characters
DOS only uses uppercase
You cannot use spaces
A single period separates the file extension from
the filename
You cannot use these characters:
/ \ : * ? “ < > | + = ; , [ ] The Full Path What does it mean? The complete path from the root of the files
system to the desired object. Use \ (vs. /) C:\ - the root
For Example;
E:\BSIT\6th Semester\System Administration\File
System.ppt File Names continued Filenames consist of two parts Main part of filename Identifies the contents of the file File extension Identifies the file type
The last period separates the file extension from
the main part of the filename.
Windows typically associates a file extension with
an application installed on a computer Folder Names Folder names follow the same guidelines for
naming files Folder names usually do not have a file extension File Operations create : find space on disk and make entry in
directory
write : write to file, requires positioning within the
file
read : read from file, involves positioning within
the file
delete : delete directory entry, reclaim disk space
reposition : move read/write position the OS must maintain
information about all open
files file pointer : the current position of the read/write
pointer in the file
disk location : the location of the file on the disk
file open count : keep track of number of
processes currently accessing the file such a table of information allows the OS to
enforce policies such as only one process can
write to a file at a given time File Structure
files can be stored physically as Bytes Lines records
whatever entity is stored, OS must map
into a disk sector
because on a physical disk, sectors are
smallest writeable unit access methods: sequential : information in the file is accessed from first
to last
readNext , writeNext , reset
direct : possible to reposition read/write pointer to any
position
such files are generally made up of fixed-length records
readRecord N, writeRecord N, positionAt N, reset
indexed : built on top of direct access, but accesses
records in file using a key
each record has a key associated with it, an index of keys
is stored with the file
readRecord KEY, writeRecord KEY, positionAt KEY, reset FAT???
file allocation table – where the OS records how the
disk space is used locates the file allocation table near the beginning
of the volume the location of the FAT is specified in the boot
sector (BIOS Parameter Block) actually, 2 copies of the FAT are stored for
redundancy the FAT number refers to the number of bits per
table entry File Systems FAT12: The earliest version the file system,
FAT12 allows a partition to contain up to 4096MB/
(212)clusters. FAT 16: oldest, created for DOS, supported by FAT 32: supports disks from 512MB to 2TB, most OS’s, cannot be installed on partitions larger than
2 GB, or on hard drives larger than 4GB. compatible with Windows 98 and up Contd.. the FAT number refers to the number of
bits per table entry
FAT12 -> 212 = 4M different clusters
can be addressed (used for floppy disks)
FAT16 -> 216 = 64M different clusters
can be addressed (MS-DOS compatible)
FAT32 -> 228 = 256G different clusters
(4 bits are reserved) Advantages of FAT File
System The FAT file system is best for drives and/or
partitions under approximately 200 MB It is better to format system partition as FAT Disadvantage of FAT File
System . It is not better to use FAT on partitions that are greater
than 200 megabytes. FAT partitions are limited in size
to a maximum of 4 Gigabytes (GB) under Windows NT
and 2 GB in MS-DOS.
Any FAT partitions that use DOS-based disk
compression (such as DriveSpace) will not have
readable files when running Windows NT
The FAT file system is also prone to fragmentation NTFS New technology file system
Better file security (Encrypting File
System),
Disk compression- can compress a
file/folder, any Windows app will
automatically expand as needed
Disk Quota features- Can enforce
quotas on disk usage Contd..
Recovery features-each file operation
broken down into atomic transactions.
maintains a transaction log – updates
disk after each transaction
if failure occurs during a transaction, info
is sufficient to complete or rollback
if a bad sector is found when writing, will
automatically map to a different sector NTFS volumes can not be accessed
by DOS,
or Windows 95 or Windows 98. Advantages of NTFS Large disks and large files: NTFS is
best for use on volumes of about 400 MB or more Recoverability: The recoverability designed into NTFS is such that a user should
never have to run any sort of disk repair utility on
an NTFS partition. Security: NTFS uses the Windows NT object
model to enforce security. An open file is
implemented as a file object with a security
descriptor that defines its security attributes. General indexing facility: NTFS
associates a collection of attributes with each file.
The set of files in the file management system is
organized as a relational database, so that files
can be indexed by any attribute. Disadvantages of NTFS It is not recommended to use NTFS on a volume
that is smaller than approximately 400 MB
Currently, there is no file encryption built into
NTFS – encryption is available as an external
option .
It is not possible to format a floppy disk with the
NTFS file system File Systems The operating system keeps track of data
(documents, pictures, etc.) by placing it into a file.
To store and retrieve files: Disk divided into tracks Tracks are divided into sectors Sectors grouped into clusters
Number of sectors in a cluster is determined by
Size of the hard drive
File allocation system – FAT, FAT32, NTFS Tracks
Sectors
within a
Track Cluster Clusters? A cluster, also known as an allocation unit , consists
of one or more sectors of storage space, and
represents the minimum amount of space that an
operating system allocates when saving the contents
of a file to a disk.
The number of sectors per cluster is dependent on Type of disk (floppy disk, hard disk)
Version of operating systems
Size of disk Every sector contains 512 bytes. (NTFS does allow
you to change this number.)
The number of clusters per disk is determined by the
filing system (FAT 16, FAT 32 or NTFS). DRIVE SIZE FAT 16
Cluster Size FAT 32
Cluster Size NTFS
Cluster Size 260 to 511
MB 8 KB Not Supported 512 bytes 512 to 1023
MB 16 KB 4 KB 1KB 1024 MB to 2
GB 32 KB 4 KB 2 KB 2 to 4 GB 64 KB 4 KB 4 KB 4 to 8 GB Not Supported 4 KB 4 KB 8 to 16 GB Not Supported 8 KB 4 KB 16 to 32 GB Not Supported 16 KB 4 KB >32 GB (up to 2 Not Supported 32 KB 4 KB TB) OS and File System
Compatibility
Operating System FAT16 FAT32 NTFS Windows XP Windows 2000 Windows NT Windows 95, 98, ME Windows 95 MS-DOS What happens during the
Formatting Process? OS creates four tables in the 1st sectors
Boot Record – the name & version number of the
OS, info. on the physical characteristics of the disk
Master File Table #1- keeps track of
Available clusters
Clusters that contain data
Clusters that are defective
Clusters that contain OS files
Master File Table #2 – copy of MFT #1
Directory Table – top level folder and file
information Formatting Process, cont. Full Format lays down new tracks and sectors
Verifies the integrity of each sector By doing a surface scan – OS will put dummy
data into sectors and then try to read the
sector Quick Format Removes files
Does not check for defective sectors Formatting Process, cont. Should you
format brand
new
preformatted
disk? Registered Files A file that is associated with an application on
your computer via its file extension. Where is this information kept? THE REGISTRY – a database that consists of a set
of files where Windows XP stores your computer’s
hardware, software, network, security,user
settings or profiles, and property settings for
folders and programs. Compare FAT and NTFS
File System Compatibility
Only Windows NT supports NTFS partitions ,
Windows NT and Windows 95 supports both NTFS
and FAT Volume size FAT supports partition sizes only up to 2 GB , the
maximum size of an NTFS partition is 16 EB Fault tolerance Windows NT offers software support for several
alternate disk-access methods that increase
speed and/or fault tolerance, While FAT does
maintain two copies of the file-allocation table, in
case one copy is damaged, it’s incapable of
automatically fixing errors) File compression NTFS has its native support for file compression,
It offers you the chance to compress individual
files and directories of your choice The system partition A better solution is to format your system partition
as FAT because NTFS partitions are accessible only via
Windows NT. If you have a fatal error with Windows
NT, you can’t simply boot a system disk to a
command prompt and fix a problem on an NTFS
partition Converting to NTFS In MS-DOS type command: CONVERT drive:
/FS:NTFS Security
NTFS has a built-in security system , FAT has no
local protection, it only has the share permission
(protect the file from network Ext3 third extended file
system Stephen Tweedie
November,2001
Journaled file system commonly used by linux.
(journaling capability means no worrying about
metadata corruption. What is most noticeable is
that you can switch back and forth between ext2
and ext3 on a partition without any problem: it is
just a matter of giving the mount command the
right file system type. ) Advantages
(over ext2 file system) Simple
Have the facility of backup and restore data
journaling improves reliability
indexing for larger directories. Size limits
Block
size
1 KB Max file
size
16 GB Max filesystem
size
2 TB 2 KB 256 GB 8 TB 4 KB 2 TB 16 TB 8 KB 2 TB 32 TB Journaling levels
There are three levels. Journal (lowest risk)
Ordered (medium risk)
Write back (highest risk) Both metadata and file contents are written to the
journal before being committed to the main file
system. Only metadata is journaled; file contents are not, but
it's guaranteed that file contents are written to disk
before associated metadata is marked as committed
in the journal. Only metadata is journaled; file contents are not.
The contents might be written before or after the
journal is updated. Thanks!!!!!!!!!!