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Establishing the Maximum Speed of a CD-ROM Drive
UnknownSoldier writes "Ever wondered how fast CD-ROM drives can spin their CDs before the CD will self destruct due to centrifugal force? This person was too, and has his results. (So much for those 100x drives)."
Contrary to popular belief, plastic doesn't last forever.
And since CD is made up of two layers of clear plastic, sandwitching a thin wafer of metal media inside, the more the CD is aged, the weaker the plastics of the CD become.
And so, the maximum spinning speed for a CD depends on how old the CD is.
I do have some pretty old CDs from the early 80's, and I will NOT put them in my 52X CDROM drive. Unless of course, I want to scrap bits and pieces out of my machine.
Muchas Gracias, Señor Edward Snowden !
That is old technology, trying to mimic an LP and it needs to be changed!
Instead of spinning the disk, just have one laser suspended above the CD with a splitter that alters the direction of the beam, like maybe similar in concept to a cathode ray beam. Have the "read" sensor at the focal point of a parabolic mirror covering the top of the cdrom case and fire the laser at whatever angle it takes to hit position X. The beam will bounce off the pit and either scatter or reflect back up into the mirror striking the focal point, with seek times limited only by the speed of light! Forget 100X, if you did it this way you'd be looking at 100,000,000x speeds from CDs that don't even move an inch!
"Your superior intellect is no match for our puny weapons!"
Who would want a 100x drive? I think I've sustained permenant hearing loss from the whine of my 32x drive.
The biggest problem with these sort of drives is seek time. A modern drive can read the whole CD in under 2 minutes, but it will take a good fraction of a second to jump from one part of a drive to another. This doesn't improve alot no matter how fast you spin the CD.
A far better solution would be to build a CD with a 640 MB Cache, and have it just read the whole thing into RAM.
Given the price of RAM over the next few years, this sort of technology should available soon.
Alternatively, it could be written into the OS itself. The only problem with this could be with some copy protection systems perhaps.
Michael
There is no cryptographic solution to the problem where the intended receiver and the attacker are the same entity.
The spin rate seems like it is turning into a consumer numbers game, like CPU speed is/was doing for a while. People who don't know any better compare the raw CPU frequency rates.
It seems at the higher CD speed it takes too long spin the thing up to reading speed anyhow. If it did not need to spin so fast, then it may be able to get smaller chunks of information sooner.
Most don't seem to be able to read until full speed is reached. Why can't they read during the spin-up time also? Too hard to calculate?
Is there a way to set the speed of CD readers slower if one wants this? I have not seen any setting options, but each vendor may be different.
Table-ized A.I.
Interesting idea. What would the max spin be on the laser tho? and would stablizing the laser in its spin be difficult or even worth the added read speeds? More importantly, would this cost more than the whole cache-approach? Hell, you could probably afford cheap RAM for the cache for around what a harddrive would cost for the job, resulting in unreasonable drive speeds. Imagine a Red Hat installation in 10 seconds.
Question
http://www.ironfroggy.com/
Basically, you hold the CD still in a little bracket, and spin a tiny little curved mirror around at the center. Since the laser will bounce erratically off the surface of the CD, you would read from the disk by placing a thin glass or plastic cover over the CD with a few photosensors sensors around its edge. The returning laser (carrying the data) could strike the cover at any pount, and the internal reflection of the cover would get enough of it to the photosensors to read the data. The laser will zip all over the place, so you'd use timing to ignore the data from non-contiguous parts of the disk. The mirror could be as small as the diameter of the laser, so you could spin it much, much faster than the CD iself could withstand.
The only problem I counld think of for such a device is that I don't think normal optical media will work as expected if you read it at a low angle.
Clearly, since no one seems to have done it, it's not that great of an idea. There's probably something wrong with it that I didn't think about at the time. Oh well - I was 12, and I just wanted to listen to Paul Simon without having to worry about bumping the desk while I was doing my cursed multiplication tables.
In spite of the suggestions and all the tests that I have made, I have not cavato a spider from the hole.
In fact it's basically possible to get instant loads - it only depends on how creative you get.
Just like the bandwidth vs latency issue in network connections, all we need to do is add more data paths.
Can't spin the disc at 100x? Well, spin it at 50X and use 2 lasers (I know the first 50x drives did something like this, they were just REALLY buggy at the time). Can't spin at 200X? Use 4 lasers. Can't fit any more lasers in? Take a picture!
I'm really amazed that we don't have these already actually - we'll need em sooner or later, unless we change to all solid state electronics...
This is a good way to get a fast CDROM drive:
This is based on these rough figures:
Assuming that the scanner is faster than the firewire (400Mbps) and 10% overhead for the data transfer, each cd image will be approx. 7.3 billion bits, taking just over 20 seconds to transfer. This device is a 2,466x speed CDROM "drive". Put that in your Pentium and smoke it! Scanner and algorithm design left as an excercise for the reader.
The Kenwood 72x drive is quite fast.
What it does is to spin the drive slower, but read 7 tracks in parallel. Now if they could get two read heads like this, it would be a 142x drive without having to spin the cd any faster.
Here's the info.
This is actually what happens with Linux; it's called the buffer cache and page cache. One's (disk-)block oriented and the other's (memory-)page oriented. They work (well) with other media, too. I'll stay scarce on the details since a) I don't know them and b) it's probably changing in 2.5
Lots of SCSI disks, controllers, and (yes) cdroms have their own ram cache. Just not 640MB worth.
A friend of mine worked at CompUSA for a couple of months. He said that people would frequently return certain brands of CDRWs because the discs would shatter in their drives. I forgot which brand exactly, but I think it was some of those cool looking black CDs.
-- dan.sherman