Re: MD: Making MP3/CD equivalent to Minidisc

[Eric Woudenberg, Minidisc.org Editor]

"David W. Tamkin" <[EMAIL PROTECTED]> writes:

> Rick wrote,
> 
> | So the MP3/CD players
> | would have to start handling UDF filesystems, or some other filesystem
> | that supported random read/write access to the media.
> 
> At least one of the players to which Michael has posted a link already
> supports UDF, and several can read CDRWs.
> 
> | Does anyone know what the minimum
> | write/overwrite size is [for UDF]? On Minidisc it's one "cluster"
> | (36 sectors == 2 seconds of SP mode stereo audio [1 sector == 2332
> | bytes]). This would define how much waste there is during editing and
> | re-recording.
> 
> Another factor is how small a contiguous space UDF will use.  MD will not
> write into an open space smaller than six clusters.

But that is just a convention that was established to accomodate the
(longish) seek times of MD gear, only the one cluster minimum write
size is an actual requirement of the MD media's physical interface
(see http://www.minidisc.org/minidisc_faq.html#fragmentation).

Actually I looked at the UDF 2.0 spec and answered my own question:
Apparently the minimum physical write size is large (it depends upon
the packet size set at format time), since there is 14KB wasted for
every packet. But the spec (see
http://www.osta.org/specs/pdf/udf201.pdf, pp. 136-137) says:

    o The packet length shall be set when the disc is formatted. The
      packet length shall be 32 sectors (64 KB).

    o The host shall perform read/modify/write to enable the apparent
      writing of single 2K sectors.

and

    6.10.2.5 Read Modify Write Operation 

     CD-RW media requires large writable units, as each unit
     incurs a 14KB overhead. The file system requires a 2KB
     writable unit. The difference in write sizes is handled
     by a read-modify-write operation by the host. An entire
     packet is read, the appropriate portions are modified,
     and the entire packet written to the CD.  Note that
     packets may not be aligned to 32 sector boundaries.

So, CD-RW using UDF has an effective 2KB overwrite unit. This is fine
and allows for an even greater granularity of write access than
MD. I don't know how robust read modify write will be in the face of
field conditions (vibration, low battery power), but it should be
possible to accomplish it none-the-less.

Michael Hoffman writes:

> Just as the cassette didn't make sense in the digital age, the
> merely "Mini" CD doesn't make sense in today's micro-sized world.
> With DataPlAy you talk of a core engine, the minimal physical
> housing into which the disk is inserted -- it's so small that you
> can flexibly shape the product user interface packaging in any shape
> around the engine, while keeping a small case.

So Michael, it seems you've now moved on to DataPlay and DVD density
discs as the thing to rest your heart upon. After you find out how
little access the recording industry will be giving you to your data
when stored in these formats, come on back and we can pick up this
discussion again. :-)

Rick


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