1. Contents Of Boot Sector
2
3
4
1
6 5
7
11
8
10
9
12
13 14 15
16
17
18
Boot Parameters
Disk Bootstrap
Program
SSiiddee 00,, TTrraacckk 00

2. Description
Boot Parameters
Jump Instruction 3
360
Kb
1.2
Mb
1.44
Mb
No.
of
bytes
EB3490
MSDOS5.0
System ID 8
No. of bytes/sector 2 512 512 512
No. of sectors/cluster 1 2 1 1
No. of sectors in reserved area 2 1 1 1
No. of copies of FAT 1 2 2 2
Max. no. of root dir. entries 2 112 224 224
Total no. of sectors 2 720 2400 2880
Media descriptor 1 FD F9 F0
No. of sectors/FAT 2 2 7 9
No. of sectors/track 2 9 15 18
No. of sides 2 2 2 2
No. of hidden sectors 2 0 0 0

3. Reading Boot Sector
No. of
Description bytes
Jump Instruction
System ID
Bytes/sector
Sectors/cluster
Sectors in
reserved area
Copies of FAT
Max. root dir. entries
Total no. of
sectors Media
descriptor
Sectors/FAT
Sectors/track
Sides
3821212212222
main( )
{
struct boot
{
char jump[ 3 ] ;
char sysid[ 8 ] ;
int bps ;
c .h. ar spc ;
char rest[ 482 ] ;
} ;
struct boot b ;
printf ( ”Insert disk,
Press any key ) ;
getch( ) ;
.a b. sread ( 0, 1, 0, &b ) ;
}
BBPP
DDBBPP
Side 0,
Trk 0,
Sec1
Side 0,
Trk 0,
Sec1

4. # include ”dos.h”
main( )
{
struct boot
{
char jump[ 3 ] ;
char sysid[ 8 ] ;
int bps ;
char spc ;
. .
} ;
struct boot b ;
absread ( 0, 1, 0, &b ) ;
for ( i = 0 ; i <= 2 ; i++ )
printf ( ”%X”, ) ;
b.jump[ i ]
for ( i = 0 ; i <= 7 ; i++ )
printf ( ”%c”, b.sysid[ i ]
) ;
printf ( ”Bytes/sector = %d”, b.bps ) ;
printf ( ”Sectors/cluster = %d”, b.spc ) ;
}
int i ;
......CCoonntt

5. In General
absread (drive no., no. of sectors to read,
sector from where reading should begin, buffer )
absread ( 0, 1, 0, &b ) ; ;
ROM - BIOS DOS
S0, T0, S1
Every sector referred using
side, track, sector
Drive A - 0
Drive B - 1
Drive C - 128
D. r i v e D . - 1 2 9. . . .
LSN 0
LSN 36
Every sector referred using
LSN
Drive A - 0
Drive B - 1
Drive C - 2
D. r i v e D . - 3. . . .
S0, T1, S1

6. What Is
It? Description
1.44 Mb Disk
Jump Instruction
System ID
Bytes/sector
Sectors/cluster
Sectors in
reserved area
Copies of FAT
Max. root dir. entries
Total no. of
sectors Media
descriptor
Sectors/FAT
Sectors/track
Sides
Obtained
Values
Typical
Values
EB3490
IBM 3.3
512
1
1
2
224
2880
F0
9
18
2
0
102
….
20480
0
1
-24
0
2048
7
-2
0
0
8
BP
DBS
Virus

7. BBPP
DDBBSS
Anti-Viral
LLSSNN 5500
# include ”dos.h”
char a[ 512 ] ;
printf ( ”Insert infected disk, Press any key” ) ;
absread ( 0, 1, 50, a ) ;
0, 1, 0, a ) ;
}
((V ( (
main( )
{
getch( ) ;
abswrite (

8. Better...
#include ”dos.h”
main( )
{
char a[ 512 ] ; char ch = ’y’ ;
char *names[ ] = { ”O Jerusalem”, ”Yankee Doodle”,
”Robinson Cruso”, ”Eddie Murphy”, ... } ;
printf ( ”Insert uninfected disk, Press any key” ) ;
getch( ) ;
absread ( 0, 1, 0, a ) ;
while ( ch = = ’y’ )
{
printf ( ”Insert infected disk, Press any key” ) ;
getch( ) ;
abswrite ( 0, 1, 0, a ) ;
printf ( ”Another disk y/n” ) ;
} ch = getche( ) ;
}

9. Directory Sector
DDiirreeccttoorryy
SSeevveerraall eennttrriieess,, eeaacchh ooff 3322--bbyytteess
Description Size
Filename
Extension
Attribute
Reserved for Future use
Time
Date
Starting Cluster number
Size
8 bytes
3 bytes
1 byte
10 bytes
2 bytes
2 bytes
2 bytes
4 bytes
( (

10. # include ”dos.h”
main( )
{
Printing Directory
struct entry
{
char n[ 8 ] ; char ext[ 3 ] ;
char unused[ 17 ] ;
} ; long int size ;
struct entry e[ 1 6 ] ;
printf ( ”Insert disk, Press any key” ) ; getch( ) ;
absread ( 0, 1, 19, e ) ;
for ( i = 0 ; i <= 15 ; i++ )
{
for ( j = 0 ; j <= 7 ; j++ )
printf ( ”%c”, e[ i ].n[ j ] ) ;
for ( j = 0 ; j <= 2 ; j++ )
printf ( ”%c”, e[ i ].ext[ j ] ) ;
}
}
printf ( ”%ld”, e[ i ].size ) ;