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From: phillip@cbmvax.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: Making a custom Filing System
Message-ID: <1899@cbmvax.cbmvax.cbm.UUCP>
Date: Tue, 19-May-87 14:08:13 EDT
Article-I.D.: cbmvax.1899
Posted: Tue May 19 14:08:13 1987
Date-Received: Thu, 21-May-87 00:55:51 EDT
References: <8705151922.AA05483@cory.Berkeley.EDU>
Organization: Commodore Technology, West Chester, PA
Lines: 31

in article <8705151922.AA05483@cory.Berkeley.EDU>, dillon@CORY.BERKELEY.EDU (Matt Dillon) says:
> 
> 
> 	I've been able to figure out the entire filing system disk format
> (apart from some space wastage, it is quite elegant) except for the format of
> the BITMAP blocks.  Anybody know what their format is ????  Also, how does
> one take over a drive (just point me in the right direction).
A disk BitMap looks like this:
(LONG) [CheckSum] [127 longwords of bitmap.]
	The high order bits refer to high blocks respectively.
bit representation:
		0 == ALLOCATED (USED)
		1 == FREE

The first bitmap block looks like this:
[CHECKSUM][ blocks: 2 - 33 ][ blocks: 34-65] etc...
            33-18 / 17-2<------------------High order word refers to
						blocks 18-33.
					   High order byte refers to
						blocks 26-33.
					   High order nibble refers to
						....:-)

At what level do you want to take over the drive?

-phil
==============================================================================
Phillip (Flip) Lindsay - Commodore Business Machines - Amiga Technical Support
  UUCP: {ihnp4|seismo|caip}!cbmvax!phillip      - Phone: (215) 431-9180
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