Hi, everybody!
>>You are wrong: the cluster feature is available in all the versions of
>>MS-DOS, and of course also MSX-DOS, not only the higher than 4 versions.
>
>Indeed cluster have been used since the first DOS release. But for some
>reason MS-DOS introduced >32Mb partitions in version 4.0. Does anybody know
>why?
The reason is of same origin that we have on MSX: originally MSDOS could
work with 16-bit sector numbers. 65536 sectors give us this magic 32M for a
partition size.
>>SCSI, IDE, and all the MSX disk controllers uses MSX-DOS (2) for handling
>>the file system. And MSX-DOS (2) is prepared for handle only 12 bit FAT and
>>16 bit sector numbers. It is only a software problem!
>
>Yes, it's only a software problem. But a bigger software problem than you
>might think.
>Going from FAT12 to FAT16 can be done by modifying only DOS2. But that
>alone doesn't break the 32Mb partition limit. You need more bits to specify
>the sector number.
>The problem is that the current way of communicating with the hard disk
>interface is using a CALL that expects the sector number as a 16 bit value.
>So to allow >32Mb partitions, you need a new way of CALLing the hard disk
>interface. Hard disk interfaces should then be equipped with a new ROM that
>implements the new CALLing standard.
I already implemented such modifications as a draft standard. The idea is to
leave disk-io routines interface as it was, but if user gives 0xFFFF as a sector
number, read the correct 4-byte sector number from a location in the memory.
the beginning of SLTWRK in the system area is a good idea, because SLOT-0
(the main BIOS) never uses them. My hard-disk ROM implements them (I also beta-test
16bit FAT patches, but there are some DOS2 related problems).
>This is what I mentioned a few paragraphs ago. Note that this change will
>only work when hard disk inferface ROMs are changed as well.
>
>>>* the way of reading the FAT itself
>>
>>Yes, this is the main problem. Is for this that I request for information
>>about the DOS 2 internals!
>
>Hard disk interfaces exist that have DOS2 internally. Maybe the
>manufacturers of those interfaces have a source code of DOS2?
I doubt. But they probably could reverse-engineer it.
On the other hand, MISIX4 (which I believe will be finaly finished
this year) will be able to handle both >32Mb partitions and 16-bit FAT.
-- EV
==========================================================================
Egor G. Voznessenski: tubed audiophile, MSX maniac & Pendorian wannabe
Internet: [EMAIL PROTECTED]
Homepage: http://www.glasnet.ru/~msxegor
Fido: 2:5020/1385.6
****
MSX Mailinglist. To unsubscribe, send an email to [EMAIL PROTECTED] and put
in the body (not subject) "unsubscribe msx [EMAIL PROTECTED]" (without the
quotes :-) Problems? contact [EMAIL PROTECTED] (www.stack.nl/~wiebe/mailinglist/)
****
