DVD-RAM: Pretend like DVD-RW?


#1

Can a DVD-RAM be written in a way to fool old drives into being a DVD-RW and read the data?


#2

Nope.

Did you ever saw a RAM write surface?


#3

Yes. There are tiny squares.

But DVD+R has a different wobble frequency and is still compatible.


#4

I think the reflective grade is a bit different and maybe DVD-RAM costs additional money for license.

I used DVD-RAM for a short time because of easy use as an backup media but I was disappointed. Very slow writing speed (3x DVD-RAM = 1,3x write speed) and after short time often read or write problems.

Liteon stopped support of DVD-RAM in the actual DVD-writers and I can understand it, it´s an almost dead media.


#5

Obviously incorrect writing speed.
Faulty drive?


#6

My eTAU108 supports DVD-RAM.

There is nothing like DVD-RAM with 10000(×5)-100000(×3) rewriting cycles even BD-RE can not nearly match.

Even the ×12 DVD-RAM still has 2500 writing cycles, as far as I know.


#7

I started with DVD-RAM at 2004 because my Panasonic DVD-Recorder only supports DVD-R and DVD-RAM, no DVD-RW. It was OK for it because the recorder don´t need high speed for recording and playing,

But after a short time, I had more and more problems with DVD-RAM and I never touched 1000 cycles. Maybe you can get more if you never put the DVD-RAM out of the drive, never touch it, never made anything with it :wink:

And I had many different drives with DVD-RAM-functionality, problems with all.

DVD-RAM-drives makes a verify directly after writing, so it would write 3x and immediately read at 3x, so the speed is 3/2 = 1,5x in optimized case. DVD-RAM also have a defect management and if it kicks in it also slow down.

And if you write many small files on it it would slow down massive because of high access times


#8

I see.

What about the DVD+R and DVD+RW?.


#9

Panasonic was part of the DVD Forum/Consortium so at the time it only supported -R/-RW formats. They added RAM support because it was their own format.


#10

Not a faulty drive. Perfectly normal for DVD-RAM writing in write & verify mode; the default mode when using a formatted disc for packet writing. After each packet is written the drive goes back and reads it back for verification.

Reading DVD-RAM on drives which don’t support it will always be impossible (unless you can crossflash the drive to another model which does support it). Unlike all other types of DVD disc (also CD & Blu Ray), DVD-RAM does not use a single physical helical track. Instead it uses multiple tracks in concentric rings, as HDDs & floppy discs do.


#11

I know. I am actually glad about more accurate writing, but there should be the option to enable/disable it occasionally.

I imagined the same thing for DVD+RW, especially high speed media in physically limited notebook drives.


#12

You wouldn´t be happy if you write important data to DVD-RAM and if you want later read the data back and see, oops, some parts not readable. Replacing after that the defect sectors wouldn´t bring the data back.

I remember LG thought about the possibilty to deactivate the verify, but dunno if it happened.

Some specs (verify, defect management) would be meaningless without the verify after write. At this point you have still the possibility to write data again if some sectors were defect.


#13

Write & verify is not mandatory for DVD-RAM discs. They can also be written in streaming mode, in which case they are treated just like DVD+/-RW using a single continuous write pass. This is the mode used by video DVD-RAM recorders and computer drives when using disc authoring software such as Nero.

The write mode used is software dependent, but the only software I can recall which actually gives a choice of modes is CD-DVD Speed (for the disc write test), and possibly some versions of InCD (for packet writing back in the pre-Vista days).

Remember that verification should be considered mandatory for all optical disc types. A successfully completed write does not mean that the disc is readable, only the most severe disc problems will cause the write to be aborted. (Over the years I suspect that many of the reported cases of rapid disc failure & data loss were actually discs that were never readable in the first place, but were not verified after writing.) But it is quicker to write a large amount of data is one pass and verify with a second, rather than packet write.


#14

Yes, after write a verify is to recommend. I do it always before I erase the written data.

In the CD-R-days a successful write was a good sign, I can´t remember any disc which failed to read. On the other hand I had sometimes write errors and the burn process stopped.

Now a write error happens very rarely with DVD and BD, but still some discs unreadable


#15

Many of them use their HDD (if they have one) as writing buffer and finish writing in stand-by mode, as far as I know. (Panasonic?)


#16

It was a pure DVD-Recorder wihout HDD. For sure it had a small RAM to buffer, but maybe also a buffer-underrun-function


#17

That is needed for DVD-R and DVD-RW due to their low 140.6kHz (like CDs) wobble frequency.

DVD+R/+RW has a high wobble frequency (817.4kHz).


#18

Dunno, why the wobble-frequence should need it? If you record data via TV-tuner the data-rate could be very low, so the drive have to wait for new data, this would not work without buffer-underrun-protection.

But my first 12x CD-writer in year 2000 had a buffer-underrun-protection, so all DVD-writers should it have also.


#19

The higher wobble frequency doesn’t negate the need for buffer underrun recovery (suspend & resume writing at any time), indeed I can’t see how it could realistically affect buffer underruns at all.

The wobble frequency (of the pre-groove spiral moulded into the disc platter) on CD-R/RW is modulated to: A) Synchronise the rotational speed of the drive when reading/writing and B) Encode information about the blank disc, via a timecode reference (the ATIP information), primarily so the drive can use the correct settings when writing the disc.

On DVD-R/RW the wobble is the same frequency as CD-R/RW, but it is unmodulated. The additional data about the disc (MID code etc.) is instead encoded in additional pits (land pre-pit) alongside the groove.

[As far as I can see in this case the wobble frequency can still be used to synchronise the rotational speed of the drive, but I cannot see how it can aid addressing the desired location on the disc when seeking at random - so designed with sequential reading in mind (e.g. video playback) and not as well suited for data discs. But by the time the DVD-R specification was finalised DVD-RAM had already been on the market for 4-5 years and was much better suited for that, having been specifically designed as a random access computer data storage medium.]

DVD+R/RW was beaten to market by Pioneer and DVD-R, but it was much better designed and technically far superior to DVD-R/RW. Not because the wobble frequency is higher, but because of how it is used. As with DVD-R/RW the wobble frequency is constant, but by using bi-phase modulation (periodically inverting the phase of the signal) the exact location along the spiral track is encoded into the pre-groove wobble signal. This is called Address in Pre-groove and allows the drive to navigate precisely to any location on the disc, which is not possible with CD-R/RW or DVD-R/RW.

At the time DVD-R/RW and DVD+R/RW were launched, packet writing to CD-RW was very popular and for this Address in Pregroove gave DVD+RW a definite advantage. Furthermore the DVD+RW specification included bad sector management similar to a HDD (identify, mark as bad and rewrite data to a good sector), which DVD-RW lacked. (Indeed the first DVD+ drives were +RW only - second generation +R/RW capable drives only arrived some months later.) But by the time DVD writing became a mainstream activity the performance of the drives themselves had greatly improved and, with the arrival of USB flash drives, packet writing had fallen out of favour. So the advantages of Address in Pregroove were less apparent. And dual-format DVD writers the norm the format war had been settled, so the technical differences between + & - were irrelevant for most users and could safely be ignored.

It is interesting to consider what the outcome of the format war actually was. One could argue that as far as the hardware goes DVD+R/RW won. Because it is the more technically advanced it would reasonably require more advanced hardware. And as the differences between +R/RW & -R/RW are accommodated by the differences between between +R/RW & CD-R/RW (which +R/RW writers were designed to handle anyway), one can argue that a +R/RW drive can be made compatible with -R/RW by essentially ‘underclocking’ & tweaking some parameters in firmware. However the opposite would not be true - the microcontroller of a -R/RW drive designed only to accommodate a 140.6 kHz signal used for basic speed synchronisation purposes would not be capable of decoding & processing the 817.4 kHz signal with encoded address data of +R/RW, so a significant hardware redesign would be required.

So a win for the DVD+RW Alliance and DVD+R/RW? Not really. By 2007 triple-format ‘SuperMulti’ DVD writers became virtually universal (the few exceptions being disabled in firmware for cost/licensing reasons), and DVD-RAM was an official format of the DVD Forum alongside DVD-R/RW.

As far as blank media goes I would call it a win for DVD+R/RW. Dual-layer DVD-R discs were not a success. And I get the impression that +R blank discs outsold -R in Europe and throughout most of the world (although I cannot find any statistics to back this up). But DVD-R/RW would certainly have survived as it has always been the dominant format in Japan (indeed DVD+R/RW discs have always been virtually unobtainable there), thanks to widespread early adoption of video DVD recorders in the '90s and imposition of the CPRM copy management system, which requires the use of DVD-R/RW.


#20

Very interesting and informative!
Thanks.
Can you also explain this?: