Do CDs spin when registering or playing ? If not, why don’t they make square disks ? It would add burning space in the corners 
They spin.
Errrr…it’d reduce disc space, because the diagonal would have to be the same size as the diameter of an ordinary disc.
Yes, they do spin, very fast. A square disc would be more prone to disintegrating due to small defects. FWIW, I do remember seeing occassional novelty shaped-CDs many years ago, but this was before the days of highspeed CD drives.
The only “non-round” CDs I see are “business card” CDs. They are basically mini-CDs with two sides cut off so the whole thing is like a business card with rounded ends. Note that the usable data area of the disc is quite small since it’s limited to the smaller diameter.
Businesses use them for promo materials. They can fit some web pages, product lists, a little video and sound, etc. on them. I tried looking at them a couple times. They aren’t all that stable in a CD-drive. So I chucked those and refuse to take any more.
They were cool for about a month 5 years ago.
I’ve got a Laurel and Hardy CD in the shape of Oliver Hardy’s head, though my Marantz CD player warns me against playing such things as an eccentric centre of gravity on an asymmetric CD puts more stress on the spindle bearings.
All CDs have the data tracks in one tightly packed spiral, like the groove in a vinyl record.
The German company of Phantom released a CD shaped like the mask with three tracks on it. There’s a warning about not putting it in car CD-players.
The German company of CATS issued a triangular CD with the CATS logo on it, ditto.
A regular (audio) CD drive spins the disc at 200-500 RPM. Data drives run much faster - a 52x drive will be spinning at up to around 10,000 RPM.
That Laurel and Hardy shaped CD should be fine in an audio player, but I’d expect it to have severe problems in a CD-ROM drive. At best, it would vibrate like mad, make an awful racket, and the drive would sense trouble and slow down. At worst, it would break apart and possibly damage the drive, possibly ejecting small sharp bits into the room.
The warning about putting anything other than round 5.25" CDs into car players is based on the high probability that they’ll jam in the slot-loading mechanism, more than thoughts that they’d break at high speed.
The fact that they are round is a clue that they rotate. The engineers who design them know about space in the corners of a square object.
Reading a square object would require a mechanism that is much more complex than that needed to rotate and read a round one. Making square CD’s (and the machinery to burn and read them) causes many more problems than it solves.
Aye, indeed. There’s a large amount of energy in a CD spinning at 52X (a DVD at 16X is about the same rotational speed), and when they let go they really do some damage.
CD 1X is fairly leisurely, and all good tray-loading or spindle-loading players should have no problem playing wobbly shaped CDs, though the life of the spindle bearings would be reduced if it only played asymmetric discs.
I’ve never seen any DVDs that weren’t circular, probably because 1X DVD is much faster than 1X CD, and the mechs wouldn’t be reliable enough.
People, we’re missing the obvious, here: if they were square, we couldn’t call them discs. We’d have to change all those logos and everything.
If they were the same width as ordinary CDs but square, the drives would need to be wider to allow room for the corners to clear as they spun. If they were square and measured the same as a regular CD on the diagonal, they would just contain less space for data (that would just be like cutting an ordinary CD to a square shape - which can actually be done and since - unlike vinyl records - the discs are read from the centre outwards undamaged tracks would still be readable, but this venture is only likely to end in tears)
I never understood the spinning part. A vinyl record spins and transmits tiny vibrations to the needle, where they are translated into sound on an analog basis. But a CD is a digital medium, or so I thought. Accordingly I’d have expected a CD to rotate with glacial slowness, as the optical reader slowly read off the digital contents of the disk–but that’s not how they work. It seems like a basic design flaw, in that a rapidly moving part prone to breakage should have been avoided, but I’m sure the designers had a good reason for it. I’m certainly in no position to judge.
The reason that they spin so fast is so that the data can be read quickly. CDs work very much like records–except that CDs are digital. Basically, the CD is covered with microscopic bumps and valleys. Each bump stands for a 1, and each valley stands for a 0. Each 1 or 0, or bit, is read by the laser, based upon how the light reflects off of the bump or valley. If we take the average CD, which holds 700Mb of data, multiply that by 1,000,000, we get 700,000,000 bytes, or 5,600,000,000 bumps and valleys. That’s a lot. I won’t post the math for a DVD, but I think we can agree that the bumps and valleys are REALLY SMALL.
The average mp3 file is about 4Mb, or 32,000,000 bits. The laser can only read one at a time, so I’d think you’d want the CD to spin as quickly as possible. If the CD spun slowly, it would take forever for the laser to read the bits at a usable speed. That’s why faster spinning drives can read the data more quickly.
Another interesting note: the data track for CDs starts at the center of the disc and travels outward, which is the reverse of a record. The CD drive must spin faster to read the data at the center of the disc, which is why you will notice a CD drive making a lot more noise at first when reading a disc and it quieting down when it starts reading the outside of the disc.
–FCOD
icsd?
Welcome to the Straight Dope Message Boards, ratfarious! You should probably note that the thread to which you’re replying is 17 years old, and the posters may not be around any longer to respond.
That was a rather thorough reply. So I don’t know how much to add to that other than we don’t have to have the media spin anymore it’s the thing that reads it
‘Georgie’ Denbrough: Do they spin?
Pennywise: Oh, yes… They spin, Georgie…
They spin… and when you’re down here with me…
YOU’LL SPIN TOO!
Not a zombie movie, but what ya’ gonna do…
And today, you can have the same effect much more easily with an ordinary paper-based card that has a QR code on it linking to an online resource.
I’d seen a few, especially the business card cd. But the variety of novelty shapes is crazy. Everything from hearts and stars to Australia, Shania Twain, or the Millennium Falcon.