[BBC-Micro] Disc formats -- DFS/ADFS and the Master Welcome Disc

Philip Pemberton philpem at philpem.me.uk
Fri Jan 22 01:35:05 GMT 2010

Jonathan Graham Harston wrote:
> Track 0 is in the same physical place whether the drive is set to
> step 80 tracks or 40 tracks. It is formatted as a usual DFS track 0
> with the usual first 10 DFS sectors in it. 

[ADFS references]
> RISC OS PRMs p2-195 onwards. I'll type something up sometime.

One of my friends just said the same thing to me in an instant-messaging 
chat: "Phil, don't you have a copy of the PRM CD for RISC OS? And ADFS 
is the RISC OS standard format, isn't it?"


> Essentially all ADFSs - prior to long-filename ADFSs - are the
> same, the physical layout of the disk is different.

Out of curiosity, how do the LFN ADFSs differ (besides the obvious "they 
can have long filenames")?
My PRMs don't seem to cover that extension to ADFS... (these are the 
PRMs on the RISC OS Ltd "RISC OS PRMs CD" from a few years ago, not the 
PRMs on the Castle Technology Acorn C/C++ CD)

> ADFS-L 16 sectors of  256 bytes, old map, 47-entry directories
> ADFS-D  5 sectors of 1024 bytes, old map, 77-entry directories
> ADFS-E  5 sectors of 1024 bytes, new map, 77-entry directories
> ADFS-F 10 sectors of 1024 bytes, new map, 77-entry directories
> ADFS-L is sequential (all up one side, then all up the other),
> other ADFSs are interleaved (top, bottom, top, bottom, etc.)

You mean like this?
ADFS-L sector addresses --
   LBA 0 -- t00h0s1
   LBA 1 -- t00h0s2
   LBA 2 -- t00h0s3

Other sector addresses --
   LBA 0 -- t00h0s1
   LBA 1 -- t00h1s1
   LBA 2 -- t00h0s2
   LBA 2 -- t00h1s2

(notation: LBA <logical sector number> -- t<TRACK>h<HEAD>s<SECTOR>)

philpem at philpem.me.uk

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