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From: jms@tardis.Tymnet.COM (Joe Smith)
Newsgroups: comp.sys.amiga
Subject: Re: wishful? I want to write an amiga disk from a sparcstation...
Summary: Possible only if sparcstation can do entire tracks at a time
Keywords: AmigaDOS, MS-DOS
Message-ID: <842@tardis.Tymnet.COM>
Date: 1 Dec 89 06:07:37 GMT
References: <4732@nigel.udel.EDU> <1058.256ea432@csc.anu.oz>
Reply-To: jms@tardis.Tymnet.COM (Joe Smith)
Organization: BT Tymnet, San Jose, CA
Lines: 57

In article <1058.256ea432@csc.anu.oz> myb100@csc.anu.oz writes:
>Thanks again to Toivo. Now a quick question in return: According to the
>documentation that comes with MTOOLS, you can modify the (provided) source
>to write *any* type of DOS disk, provided you have the useful info on how
>the disk is structured. Strikes me that all some kind soul needs to do
>(not me - too busy FTPing animations all the time :-) ) is to
>modify the format file to write AmigaDOS disks directly !

It really should have said "any MS-DOS compatible disk", not "any DOS".

>     What is needed is the following (I think)
>	FAT#1 (whatever that is)
>	FAT#2 (ditto)
>	fat_length (hmmm....)

AmigaDOS does not have a FAT.  (A bitmap is not the same as a FAT chain.)

>       cluster_size (?)
>	number_of_clusters (?)

AmigaDOS does not use clusters.

>	DIR (sector number where directory sits)
>	dir_length (and how long it is)

It's one block in the middle of the disk, 72 words long.

Question: How does AmigaDOS put all those big long file names into 1 block?
Answer: It uses hash chains instead of a linear search.
Question: What??
Answer: Instead of having the names in the directory, it has pointers to
	other blocks which have the names and pointers to more blocks.
Question: What good is that?
Answer: Check comp.sys.amiga.tech - there were several articles on this
	subject during the week of November 27th.
Question: Does that mean the directory handling routines in MTOOLS would
	have to be rewritten from scratch?
Answer: Yep

Also, AmigaDOS puts 880K on a floppy on the same floppy that MS-DOS can only
put 720K onto.  Instead of using 9 sectors per track and leaving nice
inter-sector gaps that the floppy controller needs to be able to rewrite a
single sector without disturbing the other sectors, the Amiga uses basically
one sector per track with 11 logical blocks.  Not only that, but the start
of this giant sector does not always match up with the beginning of the
track.

Most floppy disk controller chips get extremely upset at the AmigaDOS format.
I suppose the Sparcstation could process this data if the CPU gave 100% of its
attention to reading/writing the raw data bits.  The Amiga has its custom
chips to do that sort of dirtywork without burdening the CPU.

-- 
Joe Smith (408)922-6220 | SMTP: JMS@F74.TYMNET.COM or jms@gemini.tymnet.com
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San Jose, CA 95161-9019 | humorous dislaimer: "My Amiga speaks for me."