Re: Large Drive CBM DOS Mapping Proposals

On Apr 14, 8:20 pm, Jim Brain <br...@xxxxxxxxxx> wrote:
In the beginning, there were 170kB drives, with 1 head and 8 bits were
used to hold track and sector values.

Then, came 500kB disks (8050) and the rules still held.

The 8250 and SFD1001 did not break the rules.

Later, CMD HD came along and played by the same rules. 255 tracks of
256 sectors, each with 256 bytes of data. The 16MB native partition was
born. CMD HD units also used unit number to represent what we now call
a HD partition, permitting 255 partitions, raising the maximum
referenceable disk space to 4GB or so.

But, times have changed and drives now have 200GB or more on them.



VERY TRUE! I for one, would be interested in seeing a Hard Drive (or
at least something "like it") created that could utilize spaces of at
least 50 GB or more (200 would be great).



I'm reading up on IDE64 DOS commands for block level access, and have
been looking at the proposed CMD HD DOS+ solution to creating sector
addressable partitions, but I'm interested in ideas from the community.
Some questions:

IDE64 appears to forego emulating the older DOS addressing commands in
favor of new ones (B=*), while HD-DOS+ appears to add a new byte to the
existing command syntax. One offers a clean break, while the other
offers more compatibility. Does anyone care? If so, which is preferred?




Although ease of use is "extremely convenient," compatibility ends up
being the MAIN FOCUS of the vast majority of the applications that I
mess around with over here. So I vote for "compatibility." :)




Commodore drives contain 256 byte sectors, but newer drives all
standardized on 512 byte sectors. One favors compatibility, the other
favors ease of firmware development. Should a drive represent a disk in
256 byte sectors, or 512 byte ones?




Well which ever is more compatible would be my guess.




Newer ATA-based drives can access 48 bits of sectors, and each sector is
512 bytes in length. Assuming 512 byte sectors, and assuming such a
disk is split into 255 partitions, that's 40 bits or 5 bytes of data
needed to reference a location on disk. Currently, DOS commands allow
T&S&buffer pointer. Do we add 1 or 2 more bytes?

Are there other areas to consider? Someone suggested using u0>h1 and
u0>h0 to offer other ways to increase reference space.




That sounds like it may work. Has anyone actually TRIED IT on any
drives other than the 1571? If so, I am curious as to what results
they came up with in their attempts. Could you share your experiences
with us if you have tried please?




Do we really need to worry about it? Are 16MB partitions large enough?
If not, what is large enough? 4GB?



4GB? WOW! 16 MB are "sufficient" for nearly all apps that the vast
majority of us have any use for, however, for developers, engineers,
and R&D reasons, I vote that you make them at least 2.5 GB just to
make sure. ;)




Thanks for this EXCELLENT POST, Jim!!!


Charles

Jim

.

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