Date   : Mon, 04 Oct 2004 12:14:29 +0100
From   : jgh@... (Jonathan Graham Harston)
Subject: Re: Load and execution

Andrew W <a.weston2@...> wrote:
> Did DFS require load and execution addresses for files on disc?  How
> were they stored, via a disc map?
 
DFS itself does not require load and execution addresses - it just stores
what it is given. Software that loads the files may use the load and
execution addresses. 
 
DFS Sector 0 contains the list of files on the DFS disk:
 
00-07: Disk title first 8 characters
08-0E: First filename
0F   : First filename's directory, b7=locked
10-16: Second filename
17   : Second filename's directory, b7=locked
etc.
 
DFS Sector 1 contains the files' information:
00: Disk title final 4 characters
04: Catlogue cycle (number of times disk has been written to)
05: 8*<number of files>
06: b7-b6: unused
    b5-b4: *OPT 4 value
    b3-b0: Disk size in sectors b8-b11
07: Disk size in sectors b0-b7
 
08-09: First file load address b0-b15
0A-0B: First file exec address b0-b15
0C-0D: First file length b0-b15
0E   : b7-b6: First file execute address b16-b17
       b5-b4: First file length b16-b17
       b3-b2: First file load address b16-b17
       b1-b0: First file start sector b8-b9
0F   : First file start sector b0-b7
etc.
 
Some DFSs use the unused bits to extend the catalogue, eg, HDFS to specify
subdirectories and WDFS to allow files larger than &3FFFF bytes long.
 
-- 
J.G.Harston - jgh@...                - mdfs.net/User/JGH
Badly formed email is deleted unseen as spam