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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)."
Who would want a 100x drive? I think I've sustained permenant hearing loss from the whine of my 32x drive.
The best way to accelerate a windows box is at 9.8 meters per second square.
Will the next computer snake oilish product be 'cd glue' to prevent you cds from falling apart, citing this paper? :)
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you could spin *both* the disc and the reading head (in opposite directions).
...with more lasers.
~shiny
WILL HACK FOR $$$
- 6 replies here and the site already is slashdotted.
Anyway, I think you can make cd drives that spin 4000x if you want, because it might be possible to put the cd in braces to hold it together, and/or to rotate the laser instead. Or how about using multiple lasers?
It's just like silicon transistors: There's always somebody saying there is a final physical limit we'll reach within the five years...
Often, we(they)'ll find a way around the limitation.
--- Hindsight is 20/20, but walking backwards is not the answer.
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!"
It's too bad the site is /.'ed, because I wanted to see if this lab had any job openings ...
I realize there are technical hurdles with this idea, but I think they are possible to overcome: use varying luminosity bits.
Right now what they use is On-Reflective Off-Non Reflective. If the laser was able to detect that some of the bits were at 50% reflectivity, then you'd have 2 bits of data for every bit of reflectivity on the surface.
If one were to get fancier, they could use multi-colored bits. Using 2 lasers instead of one, then one laser would read a different value than the other depending on how the surface reacted to the light. They may already be doing that today with DVD's, I'm not really sure. It's been a while since I read up on it.
I guess the real point to what I'm saying is that increasing the density of the data and the spin of the disk aren't the only two options.
"Derp de derp."
This one has no broken images.
And I quote...
The motor power required, some 300 watts, would impose a rather heavy loading on the computer's power supply, though.
I don't think I'd be comfortable with something spinning that quickly in my machine. If I tapped it accidentally, would it rip through the plastic and come flying out of my computer? Perhaps maiming bystanders? Hmmm...
The answer is not to spin the disks faster, but rather to read more of the disk in one shot. But that would increase the cost incrementally with each reading device added.
Generally, people use CDs as a one-shot deal, install to hard disk once and then never use the CD again. Though people would like to read from their CDs faster they don't want to pay 4-10 times as much for a CD Player with the mechanics to read multiple sectors at once.
Sweat
It breaks my pluginses, my precious!
I got to thinking about the problems associated with mechanical drives, and it occured to me that there may be an alternative method that has no moving parts. Ever read about how your monitor works?
The way I understand it, a burst of energy (Proton?) is fired from a gun and electro-magentically guided to hit a phosphor on the screen, causing it to light up. The electro-magentic fields are timed to cause the energy to scan across the screen so fast your brain can't see the flicker.
Imagine if somebody invented a card that worked like that. It'd look like a credit card with a grid like surface on it. You side it in to a reader, and it uses a similar technique to set bits on the surface of the card. Then another beam is used to read data back off of it.
If this is possible, the advantage to it is that there are no moving parts, so it could easily last for years. If it's a read only medium like CD, then it is *not* succeptable to scratches or wear and tear.
Whatcha think, sirs?
"Derp de derp."
Then how do they achieve those 52x drives... isn't it dangerous close to that level? (not to mention making a hell of a lot of noise -- linear velocity is on the order of 600 km/h!) Or do they use other tricks (multiple laser heads perhaps, or just very aggressive read-ahead caching?)
There's 10 types of people in this world, those who understand binary and those who don't.
Once upon a time a client of mine bought a then-SOTA Toshiba CDROM (I think it was a 32x). When it first fired up, the noise was so loud it didn't register as coming from the computer -- I kid you not, we all ran to the window to see what the neighbour was blowing up on his backyard hotrod. Needless to say, that one went back to the store.
Conversely, I have a 50x Acer that is almost silent -- it's not as loud as the case fans (which aren't too bad in that machine).
I'd made a guess a while back that 50x was probably nearing the practical limit for a CDROM drive of current technology, and seems I wasn't too far off.
~REZ~ #43301. Who'd fake being me anyway?
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.
You can Do This Yourself with a commonly available Dremel tool like I did; however, I only found the outer tracks would skew at the rated 30,000. Note that the CD hole almost fits the collett of the drill. A little electrical tape fills the gap. A few wraps and there you go. Wear eye protection and do not put anything valuable in the spinning direction, such as your body.
Was it really 30,000 rpm? I don't know, but I had the 30,000rpm dremel "overclocked" on an inverter at a much higher voltage and frequency. The speed was indeed higher than off 120VAC 60Hz current. Those cheap 300 watt inverters you can get at Walmart can be tweaked with a potentiometer and capacitor on its oscillator circuit. The circuit board layout is very modular and can be quickly seen for modifications. Maximum voltage is around 180 and frequency is around 400Hz before the slew rate overheats the transistors.
Perhaps I will try again to the point of destructon tonight.
Most (all?) CD-ROM drives over 32X already use multiple lasers to read multiple tracks at once. They usually say "multi-read" on the boxes if they use this technology. Zen research (http://www.zenresearch.com/) invented this technique, and holds patents relating to it.
Afreey and Infineon already have a 100x (TrueX) CD-Rom drive (25x DVD)", it came out in 2001...
This is the future (but who cares, we'll go solid state before it gets popular).
Imperium et libertas
Autocracy and freedom
Background
The Audio CD Standard was set sometime back in the 70's. Then, it was decided that the record should rotate with different speeds, depending on where on the record the data was read, to get a constant data transfer rate. The method is named CLV (Constant Linear Velocity), or constant transfer rate. The transfer rate of an audio CD is a mere 176 kB/s, and to reach this rate the record only has to spin with 530 rpm when reading the innermost track, and 200 rpm for the outer track.
CAV is for Whimps
To be able to publish ever increasing spin ratios, many manufacturers have resorted to CAV (Constant Angular Velocity), a method whereby the record is not rotated faster when reading inner tracks. Thus they can specify impressive spin ratios for outer tracks and sell more, but in reality the spin ratio for the inner tracks is only 37.7% of this value.
CLV is for the Tough Boys
A 64x drive using CLV would have to rotate the disc with 33,920 rpm when reading an inner track, exposing the hub of the disk to a tangential force of some 45 N/mm2. A point on the periphery of the disc will be moving with 213 metres per second, slightly more than half the speed of sound. Can the disc take that?
The answer is no. A powerful no.
At about 52x, i.e. 27,500 rpm, most manufacturer's CDs blew up in a rain of plastic particles, leaving their marks on the premises. The result was a pile of shimmering plastic chips.
He also tried Kevlar reinforcement
In our efforts of reaching ever increasing speeds, we tried to reinforce a disc with Kevlar wires. [...] It turned out our motor didn't have enough power to spin up the disc enough to explode it in one try, because the Kevlar wires consumed several hundred watts of motor power for aerobreaking. [photo] After an extended period of time (about 20 seconds) at close to 28,000 rpm, the disc blew up with a loud bang anyway, with the wires remaining on the hub, as shown in the picture. It can be clearly seen that the wires remains pointing radially from the hub. The Kevlar wires had been stretched radially and performed as intended. What made the disc explode, was the creepage of the plastic material, i.e. its stretching over time, subjected to the high g forces.
"It is a greater offense to steal men's labor, than their clothes"
well.... 2/3 is slightly more than 1/2...
If Mr. Edison had thought smarter he wouldn't sweat as much. --Nikola Tesla
You said:
"You probably already know this, but just for the record -- unless you have a defective CD
drive, it shouldn't ever try to spin an audio disc up to full speed unless you're doing digital
audio extraction. If you're merely listening to your CD, it will spin at 1X, just like any
standard CD audio player."
My experience with my CDROM and CDRW drive (Samsung 52X CDROM drive and Sony 16X/10X/40X CDRW drive) is that whenever I put a disk into it, during the SEARCH, the drives will SPIN VERY FAST - I can even hear the whrrrrrlllll sound ! - then it'll slow down, if the drive finds out that the disk is an Audio CD.
What matters is that my OLD audio CDs may NOT even survive the FAST spin during the SEARCH routine.
Muchas Gracias, Señor Edward Snowden !
Comment: None of the discs reached more than 180 m/s, but on the other hand that's about 650 km/h, the cruising speed of a jet airliner.
The cruising speed of jet airliners is 800 km/h to 900 km/h, business jets being a bit faster. Today's fast turboprops reach 500 km/h.
What they need to do is put miniature black holes in the center of the spindle to cancel out some of the centrifugal force. Also, you could let the black hole out of the CD-ROM drive when you weren't using it and it would clean your room for you!
and put the CD on the true north pole and read it from a...
never mind. that's retarded.
In spite of the suggestions and all the tests that I have made, I have not cavato a spider from the hole.
Sorry to be a physics geek here, but there's no such thing as "centrifugal" force, unless you're talking about the force caused by a centrifuge dropped from a height.
There IS "centripetal" force, that refers to the force on an object travelling in a circle, which pushes outward from the axis of said circle on an object while it's travelling about the radius. Say you're spinning a ball on a string around over your head. Your work is translated into acceleration around the axis of the circle as the ball spins around your head, but the force is perpendicular to the path of the ball at any one moment, radiating from the axis. This is proven visually by noting that as you put in more work, spinning the ball faster, the angle from vertical of the string the ball's attached to increases toward 90 degrees. See? Force pushing outward, ball moving in circle. When the string is released though (or the CD breaks up) the ball moves in a straight line matching that along which it was travelling at the moment of release -- momentum then is in action.
To repeat, no centrifugal force. For all our computer learnin', it's surprising that so few paid attention in physics 101.
The only tool you've got against psychosis is experience.
Don't spin the disk at all! Move the laser beam around, and sense pits and lands by reflectivity. You could have a spinning mirror or porro-prism, or you could have a holographic optical element, or a combination of the two to move the beam around. Since the laser beam is massless, this is a much easier solution.
Dog is my co-pilot.
http://www.qedata.se/e_js_n-cdrom.htm
I've still got a 4x CDROM on my work machine, and for installing software or playing games that run from a CD, it's plenty good enough. Only time speed becomes an issue is if I want to copy a lot of data from a CD, and then mainly because it has no cache.
~REZ~ #43301. Who'd fake being me anyway?
The focal point of the mirror would have to be far enough away from the surface of the CD so that the angle of incidence is low enough that the laser doesn't bounce off the surface of the plastic. This would make the size of the no-moving-parts CD-ROM drive pretty big.
This device would also be MORE vulnerable to physical shock then current designs due to the difficulty of aiming at that range. Current designs put the lens of the laser within a few mm of the surface, but with a big mirror it'd be more like 10-20cm. It isn't important that the accuracy of the aiming be high, but the precision does need to be so that no tracks are skipped.
This device would be useful for recovery of data from damaged disks, but not for everyday use.
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...
without having to alter existing cd fabrication technologies you could reach much higher speeds if you rotate the cd near its maximum and then rotate the laser in an opposing direction at or near its maximum. Now you can add the two maximums together and you have a MUCH faster cdrom drive.
Much louder too, of course. But getting cdreaders quiet is easy... its just that manufacturers prefer to make cheap drives instead of quiet ones.
Ever need an online dictionary?
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.
Heh, I figured I'd get either funny or off-topic, wasn't expecting to get 'informative' points.
:) *Watches his Karma roller-coaster*
I honestly meant that as a joke. Seems like every time an article like this shows up on Slashdot, there's always somebody ready to say "whats the point?"
Oh well.
"Derp de derp."
A use for all those AOL CD's that I have.
Cause after a while you have enough coasters.
-THIS SPACE FOR RENT!
I think it has something to do with JS Bach and his organ.
Uncle.
Consider me educated about centrifugal force being a fictitious force in changing frames of reference. Glad there are some smarties here to set us right.
The only tool you've got against psychosis is experience.
no comment
MSBPodcast.com The opinions expressed here are my own. If you don't like 'em... Think up your own stuff.
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.
There was a noise from the next office like toast popping, and Steve the senior consultant yelled in terror. "Has your toast popped?" I shouted? "Someone just tried to shoot me!" he replied. I walked into his office to see the occupants crowded around an open CD-ROM drive with the shattered remains of about half a CD in it. As we watched, the drive attempted to shut itself, made it about half way, and then opened again. It repeated this process about twice a minute, shutting a little more completely each time. Eventually it fully closed itself, though it is still opening and shutting regularly. We didn't find the other half of the CD (at least some of it is presumably still in the drive and is what was preventing it from closing) but we did find the front flap of the CD-ROM drive under Steve's desk, where it had fallen having been blown clear across the room, past his head, and colliding with his notice-board.
Some points:-Yarn - Rio Karma: Excellent
Seems to me that this would be an excellent way to ensure that your data is permenantly deleted...
*Condense fact from the vapor of nuance*
Did anyone notice that all the disks they destroyed except two were Corel products? Mostly CorelDRAW.
Now I've used CorelDRAW and I must say it's painful to use. So I fully understand wanting to destroy it.
But remember, Corel was an early Linux supporter, so I wonder if we should support such elaborate (one might say obsessive) distructive impulses directed against them!
I teach Physics 100A. The best way to think about Centripital "force" is: it is whatever force holds the object in circular motion. (Thus it must be directed towards the center of the circular motion). For example, the earth is held in a (nearly) circular orbit around the sun by gravity. Your car can go around a curve, and locally travel in "circular" motion and it is held in the turn by friction (unless the turn is "banked" - you know, like highway turns, then gravity assists you, also).
What is called "centrifugal" force does not exist. What is most commonly cited as a "centrifugal" force is a force which pushes things out from the center of circular motion. In fact, there is no magical force pushing things away from the center of circular motion. What you feel is called inertia: the tendancy for objects to go in a straight line unless acted on by an outside force. This is not a force, it is Newton's first law.
The expression which is *not* a force is mass times speed squared divided by radius. It is a mass times acceleration, which belongs on the "right" hand side of Newton's second law, which says: the sum of all forces equals mass times acceleration. There is an expression for centripital acceleration because by stating the object is traveling in circular motion, you are saying something about what acceleration it is experiencing: namely that the acceleration is directed inward and has magnitude equal to speed squared divided by radius. (What is called "uniform" circular motion adds an additional requirement: that the speed does not change. (The velocity is a vector, so it sure does change in circular motion!) In the case of uniform circular motion, the only acceleration is centripital (center seeking), whereas in general you can also have tangential acceleration as well which changes the speed). There are magnetic, electric, and frictional forces. There are no equations for magnetic, electric, and frictional accelerations. The live on the left hand side of Newton's second law. Each can cause circular motion, and thus can be what is refered to as a "centripital" force. In general, there may be many forces acting to hold an object in circular motion.
By the way, floW is actually right about Newton's laws not holding in accelerating frames of reference. However, we don't invoke centrifugal forces to deal with this "problem". Perhaps the author was refering to the coriolis force, which *is* a fictional force.
We use the coriolis force because the effect is rather small on Earth and it is more intuitive to view Earth as a non-accelerating system, rather than one which is rotating. You may have hear about the coriolis force in physics 101 but you likely did not compute it. To do so you need the vector product (or cross product) which generally is not used in into physics books like Giancoli, Serway or Haladay and Resnik. The coriolis force effects: storm systems, water swirling down a drain, the Foucault pendulum (in fact any pendulum, but the giant pendulums in museums which knock over dominoes or trace out lines in sand are designed with coriolis in mind and called "Foucalut's" - it has to do with velocity that the pendulum achieves), and actually is used in firing Naval guns. See, for example:
some physics stuff
There is quite a bit of confusion as to what the force is that is holding the disc in circular motion. Most forces cited are actually what will cause the disc to either speed up, or slow down. The force holding the disc in circular motion is actually the atomic forces. This is why the disc does not fly apart (each part traveling in a staight line).
By the way, I actually searched for a few minuets trying to find a decent explanation of all this on the web, but most have mistakes. I am sorry to say the only way to really learn this seems to be to get a published book like Giancoli, Serway or Haladay's books (all titled Physics or something like that).
This is actually a rather delicate issue which I don't think most physics 100 students *ever* grasp. In fact, even after careful re-reading, I may have made mistakes. Heck, I get paid to explain this stuff to people, (which is a great joy) so I hope someone gets something out of this, even if it is inexact.
Gregory G. Wood
a war on terrorism? How can we end a war on a method?
You know the fact that you can go out and buy a CD rom drive for $30 is somewhat of a modern manufacturing miracle. The optical requirements for reading CDs are very very tight, and in fact if you were to come up with a design to read a CD from scratch you'd probably end up with loads of equipment on an optics table. What really took CD's off the 'nice idea but not practical' shelf was the development of laser diodes and the floating optical head. The laser itself is adjusted via a feedback circuit that detects when the pits are starting to move out of range (since the CD's a spiral you need to slowly move out as you progress). The whole reason a CD spins is because its too hard to trace this line by moving the optics and the optics behind scanning a stationary CD with a stationary laser wouldn't fit into a bay in your computer.
Just so you know.. the laser coming out of most CDs isn't good for your eyes so if you're playing around with your CDRom drive with the case off, dont look at the laser during startup for too long.
Interesting!
However, if the CD's back layer is really 100% reflective, how come when I bring one to my eye I can see it's semi-transparent? Are you sure that all CDs work the way you said?
-- B.
This sig does in fact not have the property it claims not to have.
Make all discs out of Kevlar, the we can go out and buy 32767x drives. And be cut in half by flying CD every now and then.
Reading multiple times at the same go helps to multiply the reading spead nicely, here's a review of their product:
:/ It would have been nice to get a version with adjustable speed from 1x to 52x with their multibeam technology.
kenwood 72x drive
But it seems that Kenwood has discontinued the product
What cd-roms really need is an eject button which doesnt write home to it's manufacturer (at book rates) for permission to eject a damned disc!
How frustrating it is to push an eject button and watch a device deliberate for several seconds over SOMETHING before ejecting it's cargo!
Basically, that button means "Your work here is done", so give me the disc, OK??
Considering the fact that most software isn't exactly requiring anything higher than 4x again... is anything greater than 32x even necessary... I have a cheap 48/52/56x (can never seem to figure it out) drive that came out of an emachine i got last year (i needed a cheap 1st pc) that I slapped into my current home-made box... Not sure why, but the thing seems to like to load a lot of data off the cd, spin down for a sec or two, then spin back up and continue loading more... A very annoying pattern indeed... Leading me to question whether its the drive, or if the data is being cached somewhere in my system faster than it can be written to my HD... Anyways, with larger hard-drives, most games that would use the CD-drive to play stuff like movies and music are now copying those files straight to the hard drive... Essentially the CD-Drive is now being relegated to a massive floppy drive, install and forget! As for testing max speeds.... I heard some story about down at work (WPI PC Shop) about testing this with a drill motor or something.... Essentially the disc that was tested with pretty much disintegrated if the story is true...
Insert Sig Here
I cannot get to the story. I think it has been /.
However, I have seen 3 CD's auto-destruct in the 52X Creative CD-R in the last few months. It always happens during the spin up. The machines are sitting on a level surface, so the CD "should not" be hitting anything to cause the explosion. Judging by the posts, I assume that the limit proposed in the story is 57X, and I would agree with it.
The CD's in question are all SCO UNIX install CD's
True.
It was known as the "Williams Tube", designed by Freddie Williams and Tom Kilburn in the 1940s
One on each side.
If a laser head spins centrivical force would have to be taken into account in regards to the laser tracking action.
Having 2 laser pickups would be the go.
It makes me wonder why HDDs don't have 2 magnetic heads. That way you wouldn't need the complicated hardware/software raid setups to be able to read 'n write to the HDD at the same time.
Think a turntable with 2 stylus arms, opposite the axis from each other, & both having to track across the grooves independently from each other (of course not possible one a record but you know what I mean).
The expression which is *not* a force is mass times speed squared divided by radius.
Technically correct, however if an object is rotating around a circular path with constant speed, the force required to maintain that is mv^2/r.
For most people Force is what you feel, acceleration is what you see. Saying that there is no force there is something they just won't accept, because they KNOW there is a force there.
They also don't believe there is acceleration there, the ball on a string or disk is just turning at the same speed, it isn't accelerating.
Most people never grasp this, and for most people it doesn't matter.
This is what trained professionals are for.
Under & ontop of each platter.
I'm talking about having 2 arms, so each platter has 4 lasers reading & writing to it.
Because the pickups that are under & ontop of each platter & always lined up together, which limits what both can read at the same time to data on exactly the same spot under & ontop of the platter.
Having 2 completely seperate arms mounted 180d apart from each other arround the platter means that they could track independently in & out from each other. Of course in such a drive, each arm would still read to both the bottom & top of all the platters. So in effect there would be 4 heads per platter rather than 2.
Unfortunately it would be too much to ask of the American public...
.sig involves *dropping* it. Like I should really need to explain this to a slashdot reader?
Oh, and to the clueless: the
/Brian
Broadband is nice.
Broadband is nice but expensive. What would you rather pay, $60 for a CD-ROM drive plus an install set, or $200,000 for a house in an area served by broadband?
I rarely use my CD-ROM to install software, since 'apt-get' directly off HTTP is almost as fast
"Rarely" meaning "only for games," right? Most PC games are non-free because artists, musicians, and level designers have a tougher time accepting the free software or open source philosophy than coders do. Because they sell their product at retail, they have 700 MB (capacity of a CD) to work in rather than 20 MB (the maximum attention span of a user behind 56K). (The fact that PC games are available primarily for Windows is beside my point, partly because Wine can run the vast majority of 2D Windows games.)
Will I retire or break 10K?
...although there is fragmentation of CD-ROMs as they are spun faster and faster...
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
I had a cd that had a small crack in the plastic extending from the hole about 1 centimeter into the disc, but not extending into the silver foil.
I inserted this into a 52x cdrom drive and within 10 seconds I heard a very loud sound. I ejected the drive to find that the cd had shattered into several hundred tiny pieces.
I ended up having to shake the drive upside down (with the tray out) to remove the debris.
Amazing magic tricks
I had 2 MS Flight Sim 2000 CD's blow up in 2 different drives.
The first one was put off as a fluke, and CD and drive were replaced. When the second cd blew up and a 4" long fragment shot out and stuck into the side of a 2 year old girl walking around the computer, the fluke escalated to a real problem.
I contacted the manufacterer of the 50x drive and Microsoft to find answers, and someone to pay the medical bill, but since I'm not a lawyer, and none of the attorneys around me wanted to touch the case with a 50' pole, no answer was ever found other than "you must have put the CD in wrong" from both the drive maker and Microsoft. As if there is a way to put a CD in the drive incorrectly, and still have it read. The bill for the second explosion totaled almost $10k because of some small internal injuries needing patched to the child's intestines.
.
In your last sentence, you forgot to put "matters," "that," "survive" and "during" in all caps.
With lowering memory prices, and the fact that last years PC memory goes into next years [insert crap product here] why isn't part of the solution smarter drives?
What would be wrong with a CD-ROM which reads ahead during idle and records it's information into memory? Sometimes you wouldn't even need to spin the disk [er, disc] at all.
I've got 384 MB in my desktop and that cost about the same of a no-name CD-ROM. Offer a CD-ROM which advertises "UP TO!" a speed.
Of course you would need a gigabyte of RAM to cover most discs [some do go up to 99 Minute!] at 'on the fly' reading would be limited to the 52x. But while playing audio, mp3s, games, movies, etc there could be an awsome read ahead.
But then again my solution to computer limits is almost always making components 'smarter'. My question can fit here: "Why not use Pentium I's in CD-ROMS?"
Videocards have gotten that market attention that they have processors which are half my CPU's speed - why not have 10 components which use 350MHZ chips and let them do the work?
Modular...
Get your Unix fortune now!
That's it. I'm no longer part of Team Sanity.
Happened to an engineer at a firm in Hawaii where I was doing tech support. I was up on a ladder pulling cable when it happened and I nearly fell off, it sounded like a gunshot. I ran into his office where he was prying his 40X CDROM drive open with a leatherman. He gets it open, and there's 5/8 of a CD sitting there. The other 3/8 was at the back of the drive amidst a tangle of shattered parts. The funniest part: it was a cheapo knockoff RedHat CD from the back of some book he'd bought after I'd convinced him how cool Linux was.
- None can love freedom heartily, but good men; the rest love not freedom, but license. -- John Milton
I look at it this way: internal hard drives are now up to ATA/133. The fastest hard drives out there are hard pressed to saturate an ATA/33 pipe. The net result is that hardware manufacturers are building the Big Dig when all they need is Storrow Drive*.
The only bottlenecks that matter right now are memory and graphics speed; networking issues really lie outside the box, and even a bottom-of-the-line Celeron or Duron has more processing power than 99% of us are ever going to need. Someone tells me they're running a Clawhammer with prototype DDR400 memory, that's interesting. But it's hard for me to get excited once I realize that that SATA/150 hard drive that their prototype box includes can't saturate its own pipe to the motherboard, even with a huge cache.
/Brian
*a rather scenic 4-lane that runs along the south bank of the Charles River in Boston
Yup... they don't do it now, but they did it 12 years ago!
I saw dual-armed hard drives at Las Vegas Comdex in 1990. There was a set of heads on each side of the spindle (180 opposed). I don't remember if one set was the read heads and the others were for writing, or if each arm held both heads, or... ( I don't remember the manufacturer, either. )
The demo was neat -- a drive in a glass case with the heads flying back and forth. It was the first time I'd seen the innards of a drive while it was operating, so that image has rather vividly stuck in my mind.
"...America's great minds of today, teaching America's great minds of tomorrow. Poor bastards." -- A Beautiful Min
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.
The reflected beam will bounce off at 90 degrees to the incident beam; it will not return to your spinning mirror for neat and efficient collection.
The pits pressed onto a CD are exactly 1/4 of the wavelength of the IR light which reads them. The light is generated by a laser. The requirement for a laser is based on the fact that laser light occupies a very narrow spectrum, tighter than an LED, and certainly more so than any conventional light source with a filter.
Now, if you think about what happens to the light which falls into a 1/4 wavelength deep pit and gets reflected back out, you'll see why both wavelength and incident angles are extremely critical to the proper operating of an optical drive.
Hint for the clueless: think of degrees of a sinewave; 1/4 wavelength = 90 degrees. 2*(1/4) = 1/2 wavelength = 180 degrees. Draw two sinewaves of equal magnitude at 180 degrees to each other. For each value of x, add y1 and y2. Whaddaya get?
All the same, that was a hell of a nice effort for a 12-year-old. At the time, I wasn't inventing, I was just tearing apart old color TV sets I'd find in the garbage. Times tables suck, I agree. Calculus is fun, though, since the whole thing (first principles of differentiation) is a really cool dodge around the silly problem of not being able to divide by zero.
By the way, the lands are not binary ones and the pits are not binary zeros, as you might think intuitively. The *transition* from a pit to a land or from a land to a pit represents one value; the lack of a transition represents the other.
Fire and Meat. Yummy.
This is what I remember from Physics 101. However, I may be wrong, seeing as you are the one claiming to be the "physics geek". In any case, however, your definition is contrary to standard, correct English usage.
Actually, he's right, and you're right. The centripetal force is the force acting towards the center, which has to counteract the object's tendency to continue forward in a straight line at a given speed. The centrifugal force, of course, is the apparent push outward from the center. In actual fact, the object wishes to go 90 degrees to the radius of its circle.
Fire and Meat. Yummy.
I bought a HP ScanJet recently -- the 7400 series that has 2400 DPI optical resolution. While it scans things relatively fast at 200 - 300 DPI, if you set it higher it gets VERY slow. I even skipped using USB and plugged it into an Adaptec 2940 SCSI card... not that it scans things any quicker.
High resolutions (I'll use 1200 DPI occasionally) are leave-and-get-a-cup-of-coffee slow. If its performance is any indication, a 40,000 DPI (read on!) scan -- even a 5 inch one -- would take days.
Now, about the math here... God, it's UGLY! (There are storage and bandwidth considerations, too.)
- Area of a circle: Pi times Radius squared.
- CDs are actually 4.72 inches (12 CM) in diameter.
- The unused area in the center measures approximately 1.75 inches diameter. (Delorme Street Atlas Deluxe data disc)
- 3.14 x (2.36 x 2.36) = 17.49
- 3.14 x (.875 x
.875) = 2.40
Useful Area of a CD = 15.09 square inches650 MB is the CD standard. Let's assume perfect data integrity (HA!!), and spread those 5.452 billion bits evenly throughout the surface. Further, assume that the circular nature of the tracks isn't going to screw with these particular calculations.
- 5,452,595,200 / 15.09 = 361,338,316.766 (bits in every square inch)
- Square Root of 361,338,316.766 = 19,008.9 (minimum optical resolution of the scanner, if perfectly aligned)
CD data is packed on there at nearly 20,000 DPI! Unfortunately, it looks like the AC's right here... 10,000 DPI won't resolve the pits sufficiently. 40,000 is likely the functional minimum, and that scan's going to generate one hell of a huge image!Since we aren't doing any kind of alignment, or following any track, assume we have to scan the whole surface at full resolution.
(40,000 x 40,000) x 15.09 x 8 = 193,152,000,000 bits
193,152,000,000 / 8 (bits in a byte) / 2^30 (bytes in a GB) = ...
22.48 Gigabytes (!!!) Congratulations, the image is almost 35 times the size of the data you're trying to access! FireWire will take -- assuming that's the only thing going and you actually do get 400 Mb/sec -- just over 8 minutes to actually transfer the file. Now you have to store it on your HD, page it in and out of memory, analyze it, etc...
Ouch.
"Scanner and algorithm design left as an exercise for the reader" indeed! I don't think you'd want me involved in this project -- I'd tell you to go buy a Plextor and forget it.
"...America's great minds of today, teaching America's great minds of tomorrow. Poor bastards." -- A Beautiful Min