Formatting “Track 0 Bad” floppy
This program is used to format those floppies which have bad sectors on their track 0 and when are formatted with DOS or windows, display error messages like “Track 0 BAD”. However you can also use it to format normal floppies.
The coding of the program has been given in the disk included with this book with the name “TTFORMAT.C”. The working logic of the program is same as the program published in PCQUEST computer magazine, in February 2003 edition.
In this program, we try to make this type of floppies reusable by formatting them. The program sounds that you can handle the floppy disk even with some bad sectors on it. However, if the first sector of the disk is bad, the floppy can not be formatted.
The program rewrites all the DBR, FAT and Root Directory information. If there are bad sectors on the surface of the disk, they are marked as bad in FAT.
In the coding of the program, the structure BPB is used to writer the BIOS Parameter Block of the DBR. The structure boot_sector is used to write the DBR of the disk. The structure address_field is used for interacting with number of cylinder, heads, and sectors per track and with the size of the sector.
Different functions used in the coding of the program and their description have been given in the table given next.
Function |
Description |
Random_VolumeID( ) |
This function provides the volume ID of the disk. (How DOS generates the serial number of the floppy has been discussed next to this table) |
mark_bad( ) |
Mark bad sector using function 04H of INT 13H to verify the sectors. |
sector_no_to_physical( ) |
This function is used to Convert the number of sectors into tracks, Heads and sectors |
format_term( ) |
To terminate the formatting and exit the program |
write_boot_info( ) |
Writes the boot sector of the disk |
set_media_type_for_format( ) |
The function is used to Set Media Type For format using function 18H of INT 13H |
volume_label( ) |
The function gets the volume label to write volume label of the disk |
format( ) |
Wipes the surface of the disk during formatting as well as handling the bad sectors count. |
get_drive_parameters( ) |
The Function uses INT 13H, Function 08H to get drive parameters. |
mark_bad( ) |
Holds the information of bad cluster to mark in FAT |
ask_for_continue( ) |
Function to confirm before formatting the disk |
check_bad( ) |
Function to check if the returned status is error code for BAD sector |
error( ) |
This function Displays Error message for Corresponding error code |
lock_volume( ) |
The function is used to lock the Drive using INT 21H, function 44H and Sub function 0DH |
unlock_volume( ) |
The function is used to unlock the Drive using INT 21H, function 44H and Sub function 0DH |
physical_to_sector_no( ) |
Function is used to Calculate number of sectors from track, head and sector number |
The Volume Serial Number of the Floppy disk is calculated by the DOS according to current date and time of the system clock.
The first part of the serial number is calculated by the sum of the time (seconds and hundredths of a second) and the date (month and day). The second part of the serial number is equal to the sum of the time (hours and minutes) and date (year).
All the calculations are performed in hexadecimal system. For example, let us assume that you formatted the floppy in DOS environment at 11:16:28:65 on 10/23/2003. Now let us calculate the serial number of the disk.
The time in (seconds and Hundredths of seconds) format is
= (28 and 65)
= (1CH and 41H)
Write it as 1C41
Similarly, date in (month and day) format is
= (10 and 23)
= (0AH and 17H)
Write it as 0A17
Similarly, time in (hours and minutes) format is,
= (11 and 16)
= (0BH and 10H)
Write it as 0B10
And the year will be
= 2003
= 07D3
Now, let us calculate the serial number of the floppy disk, according to the description given before. The first part of the serial number well be (1C41 + 0A17) = 2658 and the second part of the serial number will be (0B10 + 07D3) = 12E3.
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