"Bill in Co." <not_really_here@earthlink.net> wrote in message
news:%23S8eANS4IHA.1204@TK2MSFTNGP04.phx.gbl...
> M.I.5¾ wrote:
>> "Rahul" <nospam@nospam.invalid> wrote in message
>> news:Xns9AD2D4A1AAB546650A1FC0D7811DDBC81@207.46.2 48.16...
>>> I'm always confused by DVD terminology when buying media to write on.
>>> There's DVD / DVD+R / DVD-R / DVDRW and I'm not even sure which more!
>>>
>>> Are these all really distinct technologies and formats? Or are some
>>> subsets
>>> / supersets of others? Or maybe its only backward compatibility issues?
>>> What's the best way to figure out what format my Laptop supports? Do
>>> they
>>> have varied sizes? Does it matter whether I'm writing data or movies
>>> etc.?
>>> I faintly remember there being lead-in / lead-out issues....
>>>
>>> I've never faced the problem that I bought some commercial movie etc. on
>>> a
>>> DVD and my Dell Laptop ( Inspirion E1505)'s inbuilt DVD reader /writer
>>> couldn't read it. Its a dual boot so are there any Linux-vs-Win issues
>>> too?
>>>
>>> Are these distinctions only relevant when writing disks at home as
>>> opposed
>>> to commercially stamped disks? Or maybe when reading on hardware other
>>> than
>>> "computers" (etc. DVD players etc.)
>>>
>>>
>>
>> First: the easy bit. The 'R' media is write once. The 'RW' media can be
>> erased allowing its re-use.
>>
>> A little more complex is the difference between the '-' discs and '+'
>> discs.
>> As far as you the user is concerned, except for some uses there is little
>> to
>> chose. Some older video DVD players will refuse to recognise the DVD+RW
>> discs (but will recognise DVD+R). This was the result of a deliberate
>> attempt by Toshiba to discourage the '+' format. Once rumbled they had
>> to
>> abandon it.
>>
>> For DVD-R and DVD+R, there is no practical difference other than the
>> latter
>> is written faster by some drives.
>>
>> For DVD-RW and DVD+RW there is a subtle difference in that the former is
>> eraseable at the block level only. The latter is eraseable at the word
>> level. This means that individual words can be erased and overwritten.
>> It
>> also means that if used for video, more video can be added to the end of
>> existing video and the two played through seemlessly. This cannot be
>> done
>> with the '-' format.
>>
>> If you are planning on using packet incemental format (Nero's InCD or
>> Roxio's Drag-to-disc), then DVD+RW will be much more reliable than
>> DVD-RW.
>
> Just out of curiosity, why is that? (I don't use the packet writing
> format, but am curious, and would have expected the older standard to be
> more compatible in this case, too - seems like (from a hardware viewpoint)
> it might be "simpler" to just erase the whole block, rather than the
> individual word - albeit less desireable for the user).
>

It is because the read/write head when writing a DVD-RW in the drive, can
only locate positions on the disc to within a block of data. As a result
the drive has to leave a 2 block gap between different data block to avoid
over writing previous data. It is bit hit and miss and consequently it
misses on occasions and overwrites something. If that happens to be part of
the TOC or FAT, then the disc is corrupt and unreadable.

DVD+RW is a bit more technologically advanced such that the read/write head
can locate to a word of data and accurately overwrite it. Thus the
potential for overwriting something important, whilst not entirely removed,
is vastly less likely.