One more(last) question about DOS FAT. 
Author Message
 One more(last) question about DOS FAT.

 RE> The debug commands would be something like.
 RE> L 100 1 1 1
 RE> D 100 200

 RE> That would hopefully read the start of the FAT into memory and
 RE> display the start of it. Though you will have to check the syntax
 RE> as I wrote that bit from memory.

 RE> : what I'm trying to say is... do I make an array of
 RE> : words, read a word and cut the high nibble of the high byte off? or
 RE> do I : have to "extract" 12-bits? I thought is was made up of 12-bits
 RE> but I : read a sentence in a doc that said 12-bit fats don't use the
 RE> high nibble : of the high byte... that led me to belive that it is made
 RE> up as words... : I'm very confused :(

 the 12 bit fat is stored as follows:  |  byte 1 |  byte 2 |  byte 3 | etc
                                        0000 0000 0000 0000 0000 0000  etc
                                       | first entry  | second entry | etc
 Some way or another you have managed to get hold of the pointer to the
 first sector. You have to use this value for two things:

 1 -The value of the sector on disk to load (you have to translate it first!)
 2 -Use it as a pointer into the FAT, and load the 12bits located there.
    (translation is also needed here, I thought.)

    repeat the same process, with this value, until you get FF8-FFF, which
    means last sector of file. If you get FF1-FF7 it's a bad block.

 Bye! :)

 Mr. M / Infuse

... If in panic, or in doubt: Run in circles, scream and shout.
--
| Standard disclaimer: The views of this user are strictly his own.



Sun, 02 May 1999 03:00:00 GMT  
 One more(last) question about DOS FAT.

Quote:

>     repeat the same process, with this value, until you get FF8-FFF, which
>     means last sector of file. If you get FF1-FF7 it's a bad block.

No! FF1-FF6 are valid FAT entries. FF7 only is bad block.
Also, bad block cannot be in valid FAT chain, so no need
to check if it occurs. Some example how to read a file
is on zfja-gate.fuw.edu.pl in directory "boot".

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Tue, 04 May 1999 03:00:00 GMT  
 
 [ 2 post ] 

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