Hi!
>
> The problem of writing a new disk system might be not such a huge
> problem as it might seem, and this is why:
>
> With the transition from DOS1 -> DOS2 there's been plenty of time to
> find out what programs used less known DOS1 features (documented or
> not). When you would make a list of some system variables, and go
> over this, most of you will agree that with a bit of cooperation,
> it's either possible to tell what it's for, what it does, and whether
> it's needed for compatibility somehow, or (if no-one knows anything
> about it) it's so unknown, that you can count programs that use it on
> the fingers of one hand.
Let me say more. As a writer of "non-traditional" OS for MSX i _know_
that there is a _very_limited_ number of programs that use anything
beyond F23D, F2E1, F347 and some other system variables - even in
Russia, where almost everyone was writing programs with direct access
to hardware. Most of such programs are unusable on HD anyway - they
assume that "disk" is always a 720K floppy and do many other nasty
things. For compatability it's enough to coorectly support all DOS calls
and have about a dozen of system variables on correct places.
> For instance directory/FAT sector buffers: some
> DOS1 versions keep less in the BASIC memory than other versions, DOS2
> puts most of this in the mapper -> apparantly it's okay to move MOST
> of this wherever you like, and you could surely think up a new way
> for this in a new system, without too much trouble.
During experiments i found out the necessary number of buffers
in the system area of main RAM. There are two: one FAT buffer (at leat 1
sector,
but 3 sectors for better compatability, however see my note above) and
a temporary buffer which is pointed by F34B variable. This one seems
to be used pretty heavy by applications. Sector buffer(s) for directory
and file operations can be moved elsewhere.
[...]
> Having done quite some debugging and hard thinking myself in the
> past, I think most of what should stay, is pretty well defined by
> DOS2 reference documentation, together with some system variables
> which didn't change from DOS1. Would it be so hard, to fill in some
> of the blanks together? I don't think so.
>
> Why not simply DEFINE a new disk system together, and start writing
> some of the parts already, in 'pseudo-code'?
I am joining to this project with my MISIX4 system.
[...]
> For sectornumbers: I don't like adding small pieces, if you change
> something because it became too small, make it a whole lot bigger
> right away, don't mess with a few bits extra.
I think 24 bits are enough, but let it be 32 bits.
> Frankly, I find the maximum number of drives not really a problem, I
> have no more than 5 drives in my PC as well:
> A: floppy drive
> B: virtual second floppy drive (what's it do anyway, I never use it)
> C: 1 Gig. HDD
> D: another HDD
> E: CD-ROM
> I wouldn't like messing with 20 drives on a MSX, to allow direct
> access to bigger sizes. So the problem is not this number of drives,
> but the maximum size per drive.
Correct, there is no great need for more than 5-6 physical drives
(let's be realistic - nobody will ever use 8 Gig drives on MSX),
but we may need more drive letters for ASSIGNing - to use some old
good DOS1 programs. In any case, 16 drives seem to be enough.
> FAT16 support would be nice, but it's really useless without access
> to bigger drives, so shall we figure that out first?
I also think so. FAT16 on 32 Mbyte partition will create an awfully
fragmented disk - and will do it fast.
> I have one question here: can anyone make it clear what exactly
>thoseX-Mozilla-Status: 0009 cluster numbers (FFx for FAT12, and ??? for FAT16)
> are, and what they mean?
FF7 and FFF7 means "defective sectors in cluster"
FF8 thru FFF and FFF8 thru FFFF mean "last cluster in chain"
Actualy FFF and FFFF are used but let us stick to the standard.
-- EV
[MSX Maniac][Pendorian Wannabe][Tubed Audiophile]
[email:[EMAIL PROTECTED]] [www.glasnet.ru/~msxegor]
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