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
BSD text-segment swap map
...
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.
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 .
