1. OS Boot Sequence and File System
CS 314 Operating Systems
OS Boot Sequence and File System
(implication to “Boot Sector Viruses”)
Department of Computer Science
Southern Illinois University Edwardsville
Fall, 2019
Dr. Hiroshi Fujinoki
OS-Boot/000

2. CS 314 Operating Systems
OS-Boot/000

3. (Disk I/O Subroutines)
CS 314 Operating Systems
OS Boot Sequence Step 1: Boot ROM
I/O Device
(e.g., HDD)
Mother Board
Processor
Are you there?
Are you there?
Are you there?
BIOS Codes
(Disk I/O Subroutines)
Boot ROM
POST
Device polling
OS-Boot/001

4. CS 314 Operating Systems
OS Boot Sequence Step 1: Boot ROM
OS-Boot/002

5. CS 314 Operating Systems
OS Boot Sequence Step 1: Boot ROM
OS-Boot/003

6. CS 314 Operating Systems OS Boot Sequence Step 2: Load & Execute MBR
Mother Board
Memory
Processor
Bootable
Device
BIOS Codes
(Disk I/O Subroutines)
Boot ROM
Track
MBR (Master Boot Record)
The very first physical sector
of this physical drive (disk #0, surface #0, truck #0,
sector #0)
Drive spindle hole
Sector

7. CS 314 Operating Systems OS Boot Sequence Step 2: Load & Execute MBR
Scan the partition table
Program Code Area
Find which partition has OS
Jump to the OS (OS boot sector)
(Boot Strap Loader)
Partition Information
Partition table
The type of partition (OS bootable?)
Where in this drive this partition starts
Partition Information
Where in this drive this partition starts
The type of partition (OS bootable?)
OS-Boot/005

8. Source: https://www.computerhope.com/fdiskhlp.htm

9. CS 314 Operating Systems
OS-Boot/006

10. CS 314 Operating Systems OS Boot Sequence Step 2: Load & Execute MBR

11. CS 314 Operating Systems
OS Boot Sequence Step 3: Load & Execute OS Boot Loader
Mother Board
Memory
Processor
Bootable
Device
BIOS Codes
(Disk I/O Subroutines)
Boot ROM
Track
OS Boot Sector
MBR (Master Boot Record)
The very first physical sector
of this physical drive
OS-Boot/008

12. CS 314 Operating Systems
OS Boot Sequence Step 3: Load & Execute OS Boot Loader
OS-Boot/010

13. CS 314 Operating Systems File System Implementation
Disk (Disk Platter)
 Structure of a file system
Physical Drive Capacity
OS-Boot/011

14. Jump to the first bootable partition
CS 314 Operating Systems
File System Implementation
 Structure of a file system
Physical Drive Capacity
MBR
Code
Partition
Table
Partition #1
Partition #N
  
“BOOT-strap Loader”
Logical Drive
Logical Drive
Size of a partition
The first sector for a partition
The last sector for a partition
Type of file system used for this partition
Jump to the first bootable partition
Information if a partition is “bootable”
OS-Boot/012

15. IPL: Initial Program Loader
CS 314 Operating Systems
File System Implementation
IPL: Initial Program Loader
(“Boot Strap”)
 Structure of a file system
Physical Drive Capacity
Partition
Table
MBR
Partition #1
  
Partition #N
Logical Drive
Boot
Block
Super
Block
Free Space
Management
File Allocation
Information
The Root
Directory
Other files &
directories
Logical Drive
Read (load) drive parameters
Load OS kernel files & execute them
OS-Boot/013

16. CS 314 Operating Systems
OS Boot Sequence Step 3: Load & Execute OS Boot Loader
XXXX
0000
Initial Program Loader (IPL)
“JUMP XXXX” instruction
File system type
IPL Parameters
Size of the root directory
Number of sectors available
Other information
- Cluster size
OS Loader
Load OS to memory
Initialize OS
Start the OS
(IPL Codes)
OS-Boot/009

17. (= start loading OS system files & drives)
CS 314 Operating Systems
System Boot Sequence
 You turn on power
 CPU jumps to the beginning of BIOS ROM
 CPU executes POST and initializes hardware
- Memory access latency, initialize video card, etc.
 CPU executes BIOS routine to load MBR
 CPU jumps to the routine in MBR
 MBR contains a routine (“Boot Strap Loader”) to check the partition table
- Find out which logical drive is the system boot drive
Load the boot block (“Boot Strap”) of the boot drive
and CPU jumps to it
- The boot block contains a routine to start OS
(= start loading OS system files & drives)
OS-Boot/014

18. CS 314 Operating Systems    File System Implementation
 Structure of a file system
Power-On
Physical Drive Capacity
Partition
Table
MBR
Partition #1
  
Partition #N
Logical Drive
Boot
Block
Super
Block
Free Space
Management
File Allocation
Information
The Root
Directory
Other files &
directories
Logical Drive
OS-Boot/015

19. (Disk I/O Subroutines)
CS 314 Operating Systems
Boot-Sector Viruses & Its Significance
Mother Board
Memory
Processor
Bootable
Device
BIOS Codes
(Disk I/O Subroutines)
Boot ROM
Track
Boot-Sector
Viruses
Applications OS
Loader
MBR
OS (& drivers)
Boot Strap
OS Disk
I/O library
Drive spindle hole
BIOS
Sector

20. Modify virus-detection program
CS 314 Operating Systems
Boot-Sector Viruses & Its Significance
0000
Initial Program Loader (IPL)
“JUMP YYYY” instruction
“JUMP XXXX” instruction
File system type
Initial Program Loader Parameters
Size of the root directory
Number of sectors available
Other information
- Cluster size
XXXX
Load OS to memory
Initialize OS
Start the OS
Initial Program Loader Codes
YYYY
Virus Code
Disable firewall
“JUMP XXXX” instruction
Modify virus-detection program
Modify OS system calls
OS-Boot/017

21. CS 314 Operating Systems Boot-Sector Viruses & Its Significance
OS-Boot/018

22. CS 314 Operating Systems
Tools for troubleshooting booting sequence (for MBR)
(those that let you to fix problems in MBR)
OS-Boot/019

23. CS 314 Operating Systems
Tools for troubleshooting booting sequence (for IPL)
(those that let you to fix problems in IPL)
OS-Boot/020

24. CS 314 Operating Systems
Tools for troubleshooting booting sequence (file systems)
(those that let you to fix problems in “file systems”)
OS-Boot/021

25. CS 314 Operating Systems
Tools for troubleshooting booting sequence (BIOS)
OS-Boot/022

27. CS 314 Operating Systems
OS-Boot/000