BOOTING OPERATING SYSTEM
1. Booting Process:
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The heart of a modern computer is one or more Central Processing Units.
A CPU gets its instructions from memory.
The CPU reads instruction from the BIOS and searches for the hard disks, CD
drives and other hardware.
The BIOS program looks at the first sector for boot code.
Devices that feed the initial CPU instructions are known as bootstrap media.
Booting is a process involving 2 stages:
o getting hardware up and running, and
o getting the OS and other software up and running
2. Booting a Computer:
1. Power up; computer runs POST
2. Boot sequence governed by BIOS ROM
o BIOS parameters stored in CMOS
o BIOS ROM may be password protected
3. Control passes to the MBR of the first bootable device detected
4. MBR points to boot record of selected operating system
5. Operating system takes control
3. BIOS:
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What is a BIOS?
o Basic input/output system
o Built into the PC:
 BIOS software stored permanently(*) on a ROM chip on the
motherboard
o The first code run when a PC is powered on
o Identify system devices
(*)
In modern computers BIOS chip can be rewritten, allowing BIOS software to be
upgraded.
4. POST:
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What is a POST?
o power-on self-test -- one of the first processes that a computer
undergoes when booting
o POST tests the computer to ensure that it is working as it is supposed
to.
o POST can detect some errors with the processor, motherboard, RAM
and other memory, as well as the video card.
o Most BIOS chips use a system of beep codes to indicate the POST
status to the user and each BIOS chipset uses a different code.
o The IBM PC BIOS code standard, for example, uses one short beep to
indicate a successful POST and two short beeps to indicate a POST
error while AMI BIOS uses these same beep codes to indicate a DRAM
refresh failure or parity circuit failure, respectively.
5. Plug and play BIOS:
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What is a plug and play BIOS?
o Prior to Windows 95 the BIOS was responsible for managing all
hardware devices such as the floppy and hard disk drives, serial and
parallel ports, video and network cards, the keyboard, and system
clock.
o When hardware was added to the system, the user adding the hardware
had to set a variety of parameters such as the starting address in
memory where the buffers and startup code could be found as well as
the interrupt priority level (IRQ) of the device.
o Windows 95 introduced Plug-and-Play (PnP) BIOS which automates
the process of detecting and adding hardware to a system.
o In addition to making it far easier for the user to add hardware devices
-- PnP eliminated hardware conflicts that could cripple the PC.
6. Bootstrap Illustrated:
7. First sector of a hard drive:
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The first 512 bytes on a hard drive -- aka Logical Sector Zero -- contain the
Master Boot Record (MBR).
The MBR contains the boot code and the partition table.
The partition table identifies the file system on the partitions on the disk; there
must be at least one.
The boot code processes the partition table to identity which partition is
bootable; control then transfers to the first sector, called the boot sector, of
the active partition (there can be only one). The boot sector is operating
system-specific.
8. Booting from active partition:
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Once the information in the first sector is read into memory:
o The Master Boot Record (MBR) contains the partition table and boot
code
o The boot code finds the bootable partition on this drive
o The boot code transfers control to the program on the first sector of
active partition
o The first sector of active partition is called the OS boot sector, or
Volume Boot Record (VBR)
9. Volume Boot Record:
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VBR ( OS Boot sector) contain:
o OS and volume file system-specific information.
o For example, in the FAT file system, the boot sector information
includes
 the sector size,
 cluster size,
 number of FATs,
 number of entries in the root directory,
 number of sectors in the file system,
 FAT size,
 volume serial number,
 volume label, and
 file system type.
10. Booting the OS from the MBR:
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11. Boot Code:
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The boot code in a DOS disk exists in the first 446 bytes of the first 512 byte
sector, which is the MBR.
The end of the sector contains the partition table.
Boot sector viruses insert themselves into the first 446 bytes of the MBR so
that they are executed every time the computer is booted.
The master boot record is read from the first sector of the disk, and the four
partition table entries are identified and processed.
12. Sectors beyond MBR:
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In a DOS based disk the partition table and boot code requires only one sector,
yet 63 are typically allocated for both the MBR and extended partitions
because the partitions start on a cylinder boundary.
When parts of a partition table have become corrupt, it may be necessary to
search for the extended partition tables.
To find the extended partitions, a search for 0xAA55 in the last two bytes of
a sector could be conducted.
If a sector is found to be a boot sector of a file system, a partition table may
exist 63 sectors prior to it.
13. Booting Windows XP and Server 2003:
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14. Booting Windows Vista/7:
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15. Operating System Components:
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Kernel:
OS
core
functions
Application
Program
Interface
(API):
Interface to kernel
File System and User
Interface: User/program
I/O and storage
Device
Drivers:
Interface
between
hardware and OS
Hardware
Devices:
Peripheral
devices
controllers
16. The OS and User Interface:
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OS is software that sits between the hardware and the users; this is the user
interface
o The OS also provides device drivers so that the applications can
communicate with the hardware
The kernel is the privileged central part of the OS
Well-known OS/user interfaces include
o Command line: DOS, Unix, Linux
o GUI: Windows 9x/NT/Me/2000/XP/2003/Vista, MacOS, Unix/Linux
X-Windows (Gnome, KDE)
17. Types of Operating Systems:
DOS
Windows
Single-tasking operating system
Multi-tasking, single-user. Capable of networking and resource
sharing. Used NETBEUI protocol prior to Windows 2000; largely
uses TCP/IP today
MacOS
Multi-tasking, single-user, excels at network-based resource sharing.
Used AppleTalk protocol prior to TCP/IP support; Linux-based since
OS X.
Novell
NetWare
Network operating system used for resource sharing; supports
Windows and Mac clients. Dominate NOS in the 1990s using IPX
protocol; Linux-based since NetWare v5 using TCP/IP.
Unix
Multi-tasking, single- or multi-user OS. Predominant server OS on
Internet servers; has always used TCP/IP.
Linux
Open-source, lightweight version of UNIX; many variants. Excellent
OS for resource sharing, uses TCP/IP
18. Programs and Processes:
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A program is code or executable software sitting in a file on some storage
device
o Code refers to a programming language, e.g., C++, BASIC,
VisualBASIC (VB), Perl, Java, ...
o Executable files are binary files (DOS .exe or .com) or interpreted files
(.bas, .vbs, .pl, .js, ...)
o A process (or task) is a program that is currently running
19. Application Software:
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Office applications
o Word processing, presentation graphics, spreadsheet, database
o Image, video, and sound editors
Communications software
o Web browser, e-mail, instant messaging, IRC
Entertainment
o Single-user and network-based games, music players, CD creation
20. File System:
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The file system provides the framework for storing information on disks and
other nonvolatile media (e.g., writeable CDs and tapes)
o Provides the capability to create, modify, and delete files, examine
directories, etc.
Ability to reference both the physical name and view as well as a logical name
and view
Common file systems include FAT, NTFS, ufs, ext2fs, HFS/HFS+