operating system

1. Submitted to
Ms. R. Madhubala, MCA.,
I/0 SYSTEM AND CASE STUDY
BY,
M. Lakshmi Bharathi(14BIT009)

2. Contents
 Disk Structure
 Disk Scheduling
 Disk Management
 Swap-space Management
 Swap-space use and Location
 Windows 2000

3. Disk Structure:
• Disks provide the bulk of secondary storage for
modern computer systems.
• Magnetic tape was used an early secondary storage medium
but the acces time is much slower than for disks.
• Modern disk drives are addressed as large one-dimensional
array of logical blocks,where the logical block is the
smallest unit of transfer.
• The size of the logical block is usually 512 bytes,although
some disks can be low-level formatted to choose a different
logical block size,such as 1024 bytes.

4. Disk Scheduling:
• The disk drives meeting this responsibility entails
having a fast access time and disk bandwidth.
• The seek time is the time for the disk arm to move the
heads to the cylinder containing the desired sector.
• The rotational latency is the additional time waiting for
the disk to rotate the desired sector to the disk head.
• The disk bandwidth is the total number of bytes
transferd divided by the total time between the first
request for service and the completion of the last
transfer.

5. .
The request specifies several pieces of information:
Whether this operation is input or output.
What the disk address for the transfer is
What the memory address for the transfer is
What the number of bytes to be transferred is
Disk Management:
The operating system is responsible for several
other aspects of disk management too.Here we
discuss disk initialization,booting from disk,and bad-
block recovery.

6. Disk Formating:
• A new magnetic disk is a blank slate;It is
just platters of a magnetic recording material.
• Before a disk can store data ,it must be divided
into sectors that the disk controller can read and
write .This process is called low-level formatting .
• Low-level formatting fills the disk with a special
data structure for each sector.
• The header & trailer contain information used by
the disk controller such as sector number and an
error-correcting code(ECC).

7. .
The operating system still needs to record its own
data structures on the disk.It does so in two steps.
i)The first step is to partition the disk into one or
more groups of cylinders.The operating system can
treat each partition as though it were a separate
disk.
ii)After partitioning,the second step is logical
formatting.In this step the operating system stores
the initial file-system data structure onto the disk.

8. Boot Block:
• This initial bootstrap program tends to be
simple.It initializes all aspects of the system,from
CPU registers to device controllers and the
contents of main memory and then starts the
operating system.For most computers,the
bootstrap is stored in read-only memory(ROM).
• A disk that has a boot partition is called a boot
disk or system disk.The code in the boot ROM
instructs the disk controller to read the boot
blocks into memory and then strats executing that
code.

9. Bad Blocks:
• More frequently,one or more sectors become
defective.Most disks even come from the factory
with bad blocks.On simple disks,such as some
disks with IDE controllers,bad blocks are handled
manually.For instance,the MS-DOS format
command does a logical format and as a part of
the process scans the disk to the find bad blocks.
• As an alternative to sector sparing some
controllers can be instructed to replace a bad
block by sector sliping.

10. .
MS-DOS disk layout
More sophisticated disks,such as the SCSI
disks used in high-end pcs and more workstations
an servers are smarter about bad-black recovery.
Boot block
FAT
Root directory
Data blocks
(subdirectries)

11. Swap-space Management:
Swap-space management is another low-level
task of the operating system .Virtual memeory
uses disk space as an extension of main memory.
In this section,we discuss how swap space is
used,where swap space is located on disk,and
how swap space is managed.

12. .Swap-Space Use:
swap space is used in various ways by different
operating systems,depending on the implementated
memory-management algorithm.For
instance,systems that implement swapping may use
swap space to hold the entire process
image,including the code and data segments.Some
operating systems ,such as UNIX,allow the use of
multiple swap spaces.These swap spaces are
usually put on separate disks ,so the load placed on
the I/O system by paging and swapping can be
spread over the system’s I/O devices.

13. .
Swap-space Location:
A swap can reside in two places:Swap space can
be carved out of the normal file system,or it can be in
a separate disk partition.Navigating the directory
structure and the disk-allocation data structures
takes time and extra disk
accesses.Alternatively,swap space can be created in
a separate disk partition.This approach creates a
fixed amount of swap space during disk partitioning.

14. .Swap-space Management:An Example
• Swap space is allocated to a process when the
process is started.
• Enough space is set aside to hold the
program,known as the text pages or the text
segment,and the data segment of the process.
• Two process swap maps are used by the kernal to
track swap space use. map
mmmmmmmmmm
m
...
512k
512k 512k
71k

15. Windows 2000:
Microsoft windows 2000 operating system is a
32-bit preemptive multitask operating system for Intel
pentium and later microprocessors.The success
windows NT operating system,it was previously
named windows version 5.0.
History:
In 1980’s Microsoft and IBM cooperated to
develop the os/2 operating system.Thus portability
now refers to portability Intel architecture systems.

16. Design principles:
Extensibility refers to the capacity of an
operating system to keep advances in computing
technology.Among them environmental
subsystems that can different operating
systems.An operating system is portable if it can
be moved from one hardware to another with
relatively few changes.All processor –dependent
code is isolated in a link library called the
Hardware-abstraction layer(HAL).It provides
source level compatibility to application that a
IEEE 1003.1

17. System Components:
The user-mode subsystem are in two
categories.The environmental subsystem
emulates different operating systems that was
subsystems provide security function.
Hardware –Abstraction Layer:
HAL is the layer of software that hides
hardware differences from of the operating
system,to help make windows 2000 portable.For
performance reasons,I/O drivers can access the
hardware directly.

18. Kernel:
The kernel of windows 2000 provides the
foundation for the executive and subsystems.The
kernel is never paged out of memory,and its
execution preempted.An object type in windows
2000 is a subsystem data type that has a set of
attributes and a set of operations.The thread
object is the entity that is run kernel and is
associated with a process object.Timer objects
are used to keep track of the time and to signal
timeouts when operations take and need to be
interrupted.

19. Virtual-Memory Manager:
The virtual memory operation of the windows
2000 executive is the Virtual memory
manager.The VM manager windows 2000 uses a
page-based management scheme with a page
size of the data that are assigned to a process
but are not in physical memory stored in the
paging file on disk.Windows provides an
alternative ,called a section object,to present a
block of memory.

20. I/O Manager:
I/O manager is responsible for file
systems,cache management,device and network
drivers.The I/O Manager converts the requests it
receives into a standard called I/O request
packet(IRP).Eack cache block is described a
virtual-address control block(VACB)that stores the
virtual address and offset for that view,as well as
the number of processes that are using that
manager.

21. ..
Disk driver
File system
Process
Cache manager
VM Manager
Cached I/O
data copy
Page fault
I/O
I/O manager
noncached
I/O
File I/O

22. MS-DOS Environment:
The MS-DOS environment does not have the
complexity of the other 2000 environmental
subsystems.It is provide by a win32 application
the virtual DOS machine(VDM).
File system:
Historically,MS-DOS systems have used the
file allocation table.The 16-bit FAT file system has
several shortcomings,including fragmentation,a
size limitation of 2 GB,and a access protection.

23. Volume management&Tolerance:
In windows 2000 volume called a volume
set,which can consist of up to 32 physical parts.
LCNS 0-128000
LCNS 128001-
783361
Disk C:(FAT)
logical drive D
disk
1(2.5GB)
Disk 2(2.5
GB)

24. Protocols:
The several message-block(SMB) protocol
was first introduced .The system uses the
protocol to send I/O request over the network
SMB protocol has four message types.Windows
2000 uses the data-link control(DLC) protocol to
access IBM frames and HP printers that are
connected directly to the network.The AppleTalk
protocol was designed as a low-cost connectivity
.

25. .