M.I.5¾ wrote:
> "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.

Interesting. So if this is really true, then I expect the DVD+RW has
replaced the DVD-RWs in the stores by now, but I never use them, so I don't
know.