I/O Systems And Case Study Description

1. Submitted To
Ms. R. Madhubala, MCA.,
By
G.Ramya Bharathi(14BIT046)

2. 1) Disk Structure
2) Disk Scheduling
3) Disk Management
4) Swap-space Management
5) Swap-space use and Location
6) Windows 2000

3.  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.  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.
 We can improve the both the access time and the bandwodth
by scheduling the servicing of disk I/O requests in a good
order.

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
If the desired disk drive and controller are
available,the requests can be serviced
immediately.

6.  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.
 Disk Formatting
 Boot Block
 Bad Blocks

7.  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).

8.  The operating system still needs to record its own
data structures on the disk.
 It does so in two steps.
 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.
 After partitioning,the second step is logical
formatting.
 In this step the operating system stores the initial
file-system data structure onto the disk.

9.  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 starts executing that code.

10.  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.

11. sector 0
sector 1
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)

12.  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.

13. 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.

14. 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.

15. 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
m
BSD text-segment swap map
...
512k 512k 512k 71k

16.  Microsoft windows 2000 operating system is a 32-
bit preemptive multitask operating system for Intel
pentium and later microprocessors.T
 he 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.

17.  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

18.  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.

19.  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.

20.  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.

21.  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 an 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.

22. .
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

23.  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.

24. 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)

25.  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 .