I've came across this tutorial purpotedly claiming to allow a CD ROM drive to read DVDs by changing the track pitch of the laser head on the drive;
http://www.haklabs.com/2007/modify-your-cd-rom-to-watch-dvd-movies/
Wikipedia states: "DVD uses 650 nm wavelength laser diode light as opposed to 780 nm for CD. This permits a smaller pit to be etched on the media surface compared to CDs (0.74 µm for DVD versus 1.6 µm for CD), allowing in part for DVD's increased storage capacity.", which does share some resemblance to the explanation given in the tutorial linked above, only the numbers are of by a significant margin.
en.wikipedia.org/wiki/DVD
Then, an Anandtech user claims hogwash;
http://forums.anandtech.com/showthread.php?t=1378104
So, what's the conclusion on this?
Answer
Short:
What do you think of it so far?
It's Rubbish!!! (although there is some wheat amongst the chaff).
The "mod" was published in 2007. Even if it worked there would be no economic justification for doing it. If it worked it would be only worthwhile for the sheer fun of it. If any. If it worked.
The chances that it does work seems very very low indeed. Why anyone would go to the effort of publishing what appears to be blatant rubbish I know not - but such things certainly happen all the time.
Without getting into LASER frequency specs, format differences etc, lets see what can be established just from what is said here.
(1) He claims that the CD drive spins too fast - that 32X or 40X is too fast when a DVD wants to be 4X and that it must be slowed down. This is a confusion between 2 different meanings of speed rating - but lets ignore that and examine his method.
To slow the drive he proposes removing the 12V feed and using just the existing 5V feed. The drive motor speed is electronically controlled using a brushless DC motor (see motors question of today). The motor does need a certain voltage to get enough energy to meet the applied load but the speed is in no way proportional to applied voltage. If there was so little voltage used that the applied load could not be met then the motor may run slow but the electronic controller would be desperately fighting to maintain the original speed if at all possible. This is NOT how things are done.
IF one wished to run the motor on 5V it would be very very desirable, at least [tm], to connect the DVD's yellow 12V input lead to the red 5V supply lead. Just cutting the wire kneecaps (technical term) the feed to the motor. it MAY get power feed by spurious unintended pathways, or not, but that's no way to get power feed and results would vary between brands and models.
All the above tells us that this is a load of garbage.
Need we go on? No. But lets.
(2) He claims that thee data capacity is increased by a 2:1 track spacing gain and an 0.843/0.293 = 2.877:1 pit size ratio gain. So total data capacity gain would be about 2 x 2.9 =~ 5.8:1. But CD capacity = 600 kB so new capacity would be 0.6 x 5.9 = 3.5 GB. The actual capacity of a single sided DVD is about 4.5 GB so we have another discrepancy.
(3) Now let's cheat and get Wikipedia's comment on CD and DVD speeds
This rather blows away any already non-remaining shred of credibility
- Modern Compact Discs support a writing speed of 52X and higher, and some modern DVDs support writing at 16X or higher. It is important to note that the speed of 1X in CD writing is not the same as the speed of 1X when writing to a DVD. When writing to a DVD at 1X, the data is transferred at 1,385 kB/s (1,385,000 bytes per second);[2] in contrast, a CD at 1X is written at 150 KiB (153,600 bytes) of data (CD-ROM Mode 1) per second (KiB/s).[3] Thus, in brief, one X in DVD writing speeds is about 9 times more than one X in CD writing speeds. However, these speeds are not constant, and depend on the type of data written to the disc.
Based on the above 9:1 ratio a 36X CD would have the same speed as an ~= 4X DVD = no speed change needed at all, so his speed reduction prognostications are further shown to be rubbish. But, we already knew that.
Here's an interesting Wikipedia DVD format page which gives some information.
Of relevance is this comment on pit sizes and wavelengths
- DVD uses 650 nm wavelength laser diode light as opposed to 780 nm for CD. This permits a smaller pit to be etched on the media surface compared to CDs (0.74 µm for DVD versus 1.6 µm for CD), allowing in part for DVD's increased storage capacity.
This gives a 2.16:1 pit size ratio - down from the 2.87:1 he suggests. FWIW.
So, we see that there is some approximately factual material; scattered amongst what he said, but not too much. Th largest question would be "why would anyone make up such an elaborate piece of rubbish?". It's hard to know, but people do it all the time. Caveat Emptor !!!
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