Hello, I made a perfectly good Master Boot Record and I'm now proceding to the 'partition boot record' (1st sector of partition). But I would need some more info about the BIOS Parameter Block. Is this always necessary? What fields does it contain? etc. I ran it through google a few types but found little or no useful info.
Thanx in advance, DR
BIOS Parameter Block
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Schol-R-LEA
RE:BIOS Parameter Block
Assuming you intend to make a FAT16 or FAT32 file system, yes (it's needed for FAT12, too, but you clearly aren't talking of a floppy disk if you are writing the MBR). Other filesystems have different types of headers, if any.
It could be noted that the BPB is that it was originally designed for 180K single-sided disks, and modified over time to support other types of media. This will explain certain of it's peculiarities, I think.
The BIOS Parameter Block is a data structure containing the information about the disk medium and sector structure necessary to find and read the FAT table and the beginning of the file data (more on this later).
The field names, sadly, are not standardized; Microsoft, who have changed the nomenclature more than once, currently list them as:
Field Offset Length
----- ------ ------
OEM ID 03 8
Bytes Per Sector 11 2
Sectors Per Cluster 13 1
Reserved Sectors 14 2
FATs 16 1
Root Entries 17 2
Small Sectors 19 2
Media Descriptor 21 1
Sectors Per FAT 22 2
Sectors Per Track 24 2
Heads 26 2
Hidden Sectors 28 4
Large Sectors 32 4
In addition to these, there is the 'Extended BPB', which contains useful but less critical information about the disk:
Field Offset Length
----- ------ ------
Physical Drive Number 36 1
Current Head 37 1
Signature 38 1
ID 39 4
Volume Label 43 11
System ID 54 8
Source: http://support.microsoft.com/default.as ... US;Q140418&
Offsets are zero-based. Note that, officially, the OEM ID not considered part of the BPB; I added it to the list for clarity's sake.
The MS page linked above gives a brief review of the fields values; for more detailed discussion, and some general advice, you might want to check out an earlier post of mine (http://204.215.248.28/board.jsp?message=1003); the links are at the bottom.
HTH. C&CW.
It could be noted that the BPB is that it was originally designed for 180K single-sided disks, and modified over time to support other types of media. This will explain certain of it's peculiarities, I think.
The BIOS Parameter Block is a data structure containing the information about the disk medium and sector structure necessary to find and read the FAT table and the beginning of the file data (more on this later).
The field names, sadly, are not standardized; Microsoft, who have changed the nomenclature more than once, currently list them as:
Field Offset Length
----- ------ ------
OEM ID 03 8
Bytes Per Sector 11 2
Sectors Per Cluster 13 1
Reserved Sectors 14 2
FATs 16 1
Root Entries 17 2
Small Sectors 19 2
Media Descriptor 21 1
Sectors Per FAT 22 2
Sectors Per Track 24 2
Heads 26 2
Hidden Sectors 28 4
Large Sectors 32 4
In addition to these, there is the 'Extended BPB', which contains useful but less critical information about the disk:
Field Offset Length
----- ------ ------
Physical Drive Number 36 1
Current Head 37 1
Signature 38 1
ID 39 4
Volume Label 43 11
System ID 54 8
Source: http://support.microsoft.com/default.as ... US;Q140418&
Offsets are zero-based. Note that, officially, the OEM ID not considered part of the BPB; I added it to the list for clarity's sake.
The MS page linked above gives a brief review of the fields values; for more detailed discussion, and some general advice, you might want to check out an earlier post of mine (http://204.215.248.28/board.jsp?message=1003); the links are at the bottom.
HTH. C&CW.
