Tech: How fast does a CD spin?

Subject: Tech: How fast does a CD spin?
From: Cool Beans
Date: 24 Jun 06 - 06:09 PM

It's got to be more than 78rpm.

Subject: RE: Tech: How fast does a CD spin?
From: DMcG
Date: 24 Jun 06 - 06:18 PM

I don't know how reliable this is, but I quote:

A 1X CD-ROM spins 500 times, or revolutions, per minute (RPM), at its fastest (it spins quickly when the inner tracks are being read, and slows down to around 350 RPM as the outer tracks are read.) That means that a 48X drive might attempt to spin the disk at up to 24,000 RPM.

Subject: RE: Tech: How fast does a CD spin?
From: Bunnahabhain
Date: 24 Jun 06 - 07:56 PM

I vaguely remember similar numbers from somewhere. Sounds about right anyway.

Subject: RE: Tech: How fast does a CD spin?
From: Leadfingers
Date: 24 Jun 06 - 07:59 PM

They Digitals be clever little Buggers , Baint they ??

Subject: RE: Tech: How fast does a CD spin?
From: GUEST,Jon
Date: 24 Jun 06 - 08:01 PM

I haven't a clue but that sounds incredibly fast to me. I would guess this wiki article which does suggest speeds of over 10,000RPM for a 52X (but I don't think suggests anything approaching 24,000) more likely.

Subject: RE: Tech: How fast does a CD spin?
From: IvanB
Date: 24 Jun 06 - 11:20 PM

If you're asking about the speed of an audio cd during playback, the answer is that the disc spins at a rate such that the read speed is 1.21 metres per second. Since audio cd's are read from the center to the outer edge, this translates to about 462 rpm for the innermost track slowing to about 199 rpm for the outermost. In any case, significantly more than 78 rpm.

Subject: RE: Tech: How fast does a CD spin?
From: number 6
Date: 24 Jun 06 - 11:24 PM

That's gaddamned fast!!

sIx

Subject: RE: Tech: How fast does a CD spin?
From: Dave Hanson
Date: 25 Jun 06 - 02:43 AM

I can't listen that fast.

eric

Subject: RE: Tech: How fast does a CD spin?
From: George Papavgeris
Date: 25 Jun 06 - 02:58 AM

In any case, don't try to stop it with your finger on the edge.

Subject: RE: Tech: How fast does a CD spin?
From: DMcG
Date: 25 Jun 06 - 03:13 AM

I should say, Jon, that the place I took that clip from above had several caveats, hinted at by the phrase "might attempt to spin the disk at up to 24,000 RPM". The main one was that speed is for a very brief time; there is no way it would attempt to maintain it for even a second, never mind a complete minute.

Subject: RE: Tech: How fast does a CD spin?
From: JohnInKansas
Date: 25 Jun 06 - 04:32 AM

Although it's a bit higher than redline on a typical Honda tach, 24,000 is not really an extraordinary speed for small rotating machines. It is in about the right range for the separator disks in a DeLaval cream separator used on many farms in the early 1900s. They seldom exploded.

24,000 RPM is also "synchronous speed" for a (single pole) electric motor operating on 400 Hz AC power, which is quite common in aircraft, so quite a few electric motors/generators/hydraulic pumps operate at that speed, Some of those are big enough to explode impressively... but don't often do so.

I don't have detailed specs at hand, but one thing to be noted is that there are differences in methods used by various CD drive makers. My impression is that most of them claim to use a "constant linear speed" in one form or another. Rumor is that some early model CD drives used constant rotation speed, and there may still be a few of this kind around.

The CD has to spin at a very consistent and stable speed in order to be read accurately, but that speed doesn't have to be exactly at "playback speed." The disk could be spun up to some lower speed to stuff memory buffers with the bits before the play starts, and as long as reading the track finishes before the buffers are emptied the music will be continuous. Since the bit density (bits per revolution) is lowest at the start of the CD, at the inner track, the buffer stuffing can get a pretty good head start without too noticeable a delay, even if it doesn't spin at the ~500 RPM needed for "real time" data transfer. The controller can hold back on the start of playing a subsequent track until there's enough in the buffer to get to the end of that track, so in a cheap playback drive, the track delay (dead time between tracks) may be slightly longer than theoretically was "recorded silence."

As play progresses to the outer areas of the CD, buffering can also be used to read stuff into the buffer at whatever bit rate the CD produces at that radius, with the buffer output regulated to the rate needed for the playback. This means that it is not necessary to have a different rotation speed at every radius where data must be read, and I've seen descriptions of "stepped speed" drives (advertised as constant linear speed) in which as few as 4 or 5 rotation speeds were used, with each speed used to read a "zone" on the CD, using the data buffer to provide constant bit-rate-out while the bit-rate-into the buffer varies somewhat across the zone.

The "innards" of drives are considered proprietary by the manufacturers, so they don't give out a lot of info on exactly how things work inside a given drive. As long as the signal at the connector meets the specs, it's a good drive and you're not supposed to need to worry about what's going on inside.

But they do definitely spin a bit faster than 78 RPM, even at 1X playback speed.

John

Subject: RE: Tech: How fast does a CD spin?
From: GUEST,Norval
Date: 25 Jun 06 - 01:18 PM

Here is a bit of useless information using the specification, from IvanB, of 1.21 metres per second while reading an audio CD. If the track on a full 74 minute CD was strung out along the highway it would cover 60 x 74 x 1.21 / 1000 = 5.372 km. (3.338 miles)

Hey, you may need this fact in a game of Trivial Pursuit.

Subject: RE: Tech: How fast does a CD spin?
From: Bunnahabhain
Date: 25 Jun 06 - 01:46 PM

Where as a LP has 50.6 meteres of infomation on each side. Well, if one's worth knowing, then the other is also...

Subject: RE: Tech: How fast does a CD spin?
From: GUEST,.gargoyle
Date: 25 Jun 06 - 11:48 PM

Id-Jets!!!

RAM (Random Access Memory) CHIPS

Buffer Size????

Sincerely,
Gargoyle

Perhaps, this question has merit. None of the replies have made a referral to existing answere.

Above and below is not enough.
American Trad and UK/B.S. is not enough.
I am now promoting an eight sided division to the MC

Through a gaunlet of queries (Id-Jets) first level....one could eventually pass into "Seventh Heaven"....of course, the eighth level being reserved for the Joe Offer Clones.

A truely Gaseous lack of Concept-Grasp like beans just emitted...would quickly send them down to possum-hell....for re-learning.

Subject: RE: Tech: How fast does a CD spin?
From: GUEST,punkfolkrocker
Date: 26 Jun 06 - 12:23 AM

.. it all depends on the bpm of the music and the amount of cider you been drinking..

last night the bedroom was spinning around my head at a gentle not too nausea inducing velocity..


so i could pin the cd player down long enought to shove a disc in


[sandy denny.. followed by manfred mann.. and stille volk.. to fall asleep to]

tonight my head is throbbing but the room is relatively still

like a playground roundabout being pushed by a weak asthmatic girl..



so at least the cd player is nearly staying still in one place in the corner

so it will let me put a disc in before it spins off around me again !!!

[heavens gate soundrack]



g'night.....

Subject: RE: Tech: How fast does a CD spin?
From: Artful Codger
Date: 26 Jun 06 - 02:54 AM

A direct comparison between the length of the paths would be misleading: the LP encoding is analog (the width of the groove corresponding directly to the wave amplitude), CD encoding is digital (a single sampled value is serialized as a stream of 1/0 bits along the track, and is stored redundantly for error correction.) Despite the much longer total length traversed, audiophiles generally assert that CDs are more "lossy" than LPs - the audio information contained is less, in a sense. (Actually, I suspect that there is sufficient storage space to do a superior job, but when the standards were adopted, we didn't yet have processors fast enough to handle good compression or smoothing algorithms.)

A higher sampling speed (e.g., 48x) doesn't necessarily mean the disk spins that proportionately faster than a 1x disk, since the drive can simply sample from multiple tracks simultaneously.

A much lower spin speed is needed for audio playback than most drives are capable of. Consider: when duplicating a CD, the entire contents of the CD can be read in just a couple minutes with a 48x or 52x drive. More important is for the drive speed to remain relatively constant during playback. Due to inertia, this requires far less energy and causes less mechanical stress than continually varying the spin speed, even if the drive ends up reading nothing a good part of the time.

Subject: RE: Tech: How fast does a CD spin?
From: Dave Hanson
Date: 26 Jun 06 - 03:49 AM

Gargoyle,..............chips   buffer size ? surely you meant buffet size.

eric

Subject: RE: Tech: How fast does a CD spin?
From: JohnInKansas
Date: 26 Jun 06 - 07:15 PM

Of interest (or not), the May-June 2002 issue of American Scientist included an article by Brian Hayes titled Terabyte Territory with some interesting (to me and who gives a s... about the rest of you) bits on Hard Drives. The magazine is online, but is accessible only to Sigma Xi members and/or paid subscribers. (Note there's another mag with the same name not assoc with Sigma Xi.)

[quote:]

The first disk drive was built in 1956 by IBM, as part of a business machine called RAMAC (for Random Access Method of Accounting and Control). The RAMAC drive was housed in a cabinet the size of a refrigerator and powered by a motor that could have run a small cement mixer. The core of the device was a stack of 50 aluminum platters coated on both sides with a brown film of iron oxide. The disks were two feet in diameter and turned at 1,200 rpm. A pair of pneumatically controlled read-write heads would ratchet up and down to reach a specific disk, as in a juke box; then the heads moved radially to access information at a designated position on the selected disk. Each side of each disk had 100 circular data tracks, each of which could hold 500 characters. Thus the entire drive unit had a capacity of five megabytes—barely enough nowadays for a couple of MP3 tunes.
RAMAC was designed in a small laboratory in San Jose, California, headed by Reynold B. Johnson, who has told some stories about the early days of the project. The magnetic coating on the disks was made by mixing powdered iron oxide into paint, Johnson says; it was essentially the same paint used on the Golden Gate Bridge. To produce a smooth layer, the paint was filtered through a silk stocking and then poured onto the spinning disk from a Dixie cup.

[end quote]

So DIYers - now you know how.

John

Subject: RE: Tech: How fast does a CD spin?
From: GUEST,Jon
Date: 26 Jun 06 - 07:21 PM

Amazing...

Subject: RE: Tech: How fast does a CD spin?
From: JohnInKansas
Date: 26 Jun 06 - 07:48 PM

Jon -

In the 2002 article he predicted the 1TB drive "in about 5 years." It's here now, from any of a handful of sellers, for under 1K$.

He also predicts the 120 TB drive (1,000x the 120GB one he had in hand at the time of the article) by 2012, and asks the interesting question "What .... are you gonna put on it." and "How are you going to find what's there if you do fill one up."

"You might start by copying over everything on your present disk—all the software and documents you've been accumulating over the years—your digital universe. Okay. Now what will you do with the other 119.9 terabytes?"
"If you read one book a day, every day of your life, for 80 years, your personal library will amount to less than 30 gigabytes, which still leaves you with more than 119 terabytes of empty space. To fill any appreciable fraction of the drive with text, you'll need to acquire a major research library. The Library of Congress would be a good candidate. It is said to hold 24 million volumes, which would take up a fifth of your disk"

His estimate is for plain text storage, and only for the text, but that's still a mind-wiggler.

John

Subject: RE: Tech: How fast does a CD spin?
From: GUEST,Jon
Date: 26 Jun 06 - 08:26 PM

It's funny John, the extract did get me wondering where things were going. At the moment, the most I've got in a PC is 2 x 160GB and I can't even think what I will ever use all that for let alone trying to think in terms of 120TB!

I bought the second BTW as I wanted to go dual boot with each O/S on its own disk and when I looked at prices I couldn't see any point in my getting anything smaller - it wasn't a case of need.

Of course we don't know what machines of the future may be capable of and what sort of storage whatever they can do will require...

Subject: RE: Tech: How fast does a CD spin?
From: JohnInKansas
Date: 26 Jun 06 - 09:40 PM

Jon -

The article is probably too lengthy to post, and as noted it may not be accessible for many. I scanned and OCRd it from the magazine, and haven't bothered to register my membership with the magazine, so I can't be certain it's there.

Random notes include that at the current "cost per byte" we've recently crossed the line where HD storage is cheaper than paper. He offers the opinion, without much to substantiate it, that any time the "value of the data" exceeds the "cost of the medium" an economically unstable condition exists that can't be sustained. Although he doesn't offer much argument, the premise sounds like it might be worth considering in your market investments.

"With a T1 connection, running steadily at top speed, it would take nearly 20 years to fill up 120 terabytes." He estimates "MP3 audio files run a megabyte a minute, more or less. At that rate, a lifetime of listening—24 hours a day, 7 days a week for 80 years—-would consume 42 terabytes of disk space." About the only medium currently existing that could press the capacity of a 120 TB drive would be DVD, for which: "In the format used on DVDs, the data rate is about 2 gigabytes per hour. Thus the 120-terabyte disk will hold some 60,000 hours worth of movies; if you want to watch them all day and all night without a break for popcorn, they will last somewhat less than seven years."

And note that if there's enough data freely available to fill a 120 TB drive by downloading, "you don't really need to download it." (?) The problem will be, whether the data is on your machine or elsewhere, "how do you find what you need?" He suggests that maybe the data should be free, and the "Table of Contents" is what costs you to subscribe to.

DRM is gonna be a real mess, but you can easily see why "searching and indexing" is booming.

John

Subject: RE: Tech: How fast does a CD spin?
From: Artful Codger
Date: 26 Jun 06 - 10:13 PM

Don't worry, Microsoft will find ways to max out your 120Tb drive. The OS will probably take up half the disk, cloning itself every 15 minutes for recovery (though it will still crash with annoying regularity, for compatibility with earlier versions) and a Word document will contain a Babelfish translation into every known language, along with a full-length feature movie of an animated paper clip.

Subject: RE: Tech: How fast does a CD spin?
From: GUEST,Jacqued
Date: 27 Jun 06 - 03:43 PM

Will someone please stop this cd so I can get off?????????????

Subject: RE: Tech: How fast does a CD spin?
From: The Fooles Troupe
Date: 27 Jun 06 - 05:50 PM

I thought it was spinning so fast that you have to hang on - just let go and you will be thrown off!!!

Anybody remember the old Carnival Rides that used centrifugal/centripetal force?

Subject: RE: Tech: How fast does a CD spin?
From: GUEST,GT2008
Date: 03 May 08 - 03:19 PM

AN ACCURATE WAY TO CHECK RPM OR CD SPEED WOULD BE TO USE A STROBE LIGHT THAT IS MADE TO DETECT RPM. THESE DEVICES CAN BE PURCHASED AT VARIOUS PLACES. :D

Subject: RE: Tech: How fast does a CD spin?
From: GUEST,The Mole catcher's unplugged Apprentice
Date: 03 May 08 - 03:45 PM

I remember that carnival ride. Actually there was one at a carnival that passed through this way last year., which begs the question; What would the RPM be of a CD if it was played on one of those rides while you were riding on it? Just asking *LOL*

Charlotte R

Subject: RE: Tech: How fast does a CD spin?
From: JohnInKansas
Date: 03 May 08 - 05:18 PM

The Wiki article linked by Jon way up at the toppish end of the thread my have been updated since anyone was interested in the thread (two years ago), but now includes a 1x CD spin rate:

Of course the implication of CLV, as opposed to CAV, is that disc angular velocity is no longer constant, and spindle motor need to be designed to vary speed between 200 RPM on the outer rim and 500 RPM on the inner rim.

Those probably are "round number" values, and shouldn't be taken as exact, but for a 24x disk (fairly common now) that would mean 4,800 RPM to 12,000 RPM.

McUA: Angular velocities are vectorish, so a CD on a carnival ride would spin at the same CD RPM plus/minus the ride RPM, if axes are aligned (parallel). The RPM required for the carnival ride depends on the diameter of the cage, and must be high enough to always produce a positive outward force. If the wheel rotates up to a horizontal axis, a centrifugal force of at least 0.2g is typical at the top of the cycle and produces a "feeling of weightlessness" but still keeps the idiots safely pressed into their spot on the wheel. That automatically means an apparent 2.2g at the low point. A ride that varies from 1g at top to 3g at bottom feels "much safer" and most of the rides I've seen can be run up to this level for "wimpish" riders.

Most rides I've seen of a size requiring around 20 to 60 rpm, which would make little difference to the CD with parallel axes of rotation for the ride and for the CD, as long as the ride speed is fairly constant or varies slowl enough.

If the axes are not parallel, Mr. Coriolis might disassemble (or at least render unusable) the CD and/or CD drive, just as moving it around very aggressively by hand (i.e. tipping the computer) on your desktop while it's running can do.

Since hard drives in desktop computers are fairly typically running at 12,000 RPM now all the time they're in use, the common 3.5 inch drives are very susceptible to destructive effects of movement while spinning. Most 2.5 inch drives, used largely in laptops, remain at 7,000 RPM or lower (with some exceptions) to lessen the effect of Coriolis forces/torques and other bumps and jiggles, which is one of the several reasons why laptop drives are typically about one-tenth as fast at moving data as "modern" desktop drives.

John

Subject: RE: Tech: How fast does a CD spin?
From: The Fooles Troupe
Date: 04 May 08 - 02:08 AM

"typically about one-tenth as fart"

That explains a lot about Old MudCatters... :-P

Subject: RE: Tech: How fast does a CD spin?
From: JohnInKansas
Date: 04 May 08 - 04:25 AM

Foolestroupe -

Do you need to set a more legible font on your browser?

Or are you just using that weird character set you use to talk to the little people with the big eyes that come to visit you in their shiny obloid tin can?

Or are you just blind drunk again?

Good to hear from you anyway.

John

Subject: RE: Tech: How fast does a CD spin?
From: The Fooles Troupe
Date: 04 May 08 - 04:34 AM

John,

It's our old Friend, "The One Eyed, One Horned, Flying Purple People Eater"... :-P

Subject: RE: Tech: How fast does a CD spin?
From: The Fooles Troupe
Date: 04 May 08 - 05:04 AM

"Do you need to set a more legible font on your browser?"

Me eyes ain't what they used ta be - they used ta be me ears! :-P

Subject: RE: Tech: How fast does a CD spin?
From: Tootler
Date: 04 May 08 - 05:57 PM

My father told me that during WWII, he once saw an aircraft gyroscope come off its mountings and punch a hole in several inches of concrete during a test run.

So; you have been warned [*grin*]

Subject: RE: Tech: How fast does a CD spin?
From: GUEST,hello
Date: 28 May 08 - 06:38 PM

it changes so u will never get a deffinete answer

Subject: RE: Tech: How fast does a CD spin?
From: Gurney
Date: 28 May 08 - 07:42 PM

I seem to remember 'Mythbusters' testing disks to destruction, some time ago, because of reports of disks disintegrating in drives. I wasn't paying much attention, but I think that you wouldn't want to be nearby when it happened.
They had to go faster than normal drives before they got results, if I remember correctly, using compressed-air equipment, but it did happen.

Subject: RE: Tech: How fast does a CD spin?
From: The Fooles Troupe
Date: 29 May 08 - 01:45 AM

They used a high power - power drill motor.

Subject: RE: Tech: How fast does a CD spin?
From: Joe_F
Date: 29 May 08 - 09:00 PM

Annals of cluelessness: Until fairly recently I did not know that CDs spun. I thought they stayed put and clever optics caused the laser beam to chase around them.

Reminds me of Tennyson's "ringing grooves of time". A footnote to "Locksley Hall" explains that he had recently taken his first train trip & had not noticed the rails. He was under the impression that the wheels ran in grooves.

Subject: RE: Tech: How fast does a CD spin?
From: GUEST,Bob L
Date: 30 May 08 - 11:44 AM

That may not be as dumb as it seems nowadays: the technology was still fairly young at the time, even if it had passed its infancy - and some (very) early railways did actually run in a grooved track.

Subject: RE: Tech: How fast does a CD spin?
From: Bernard
Date: 30 May 08 - 11:55 AM

Hmmm... anything that rotates will break up if you spin it fast enough, methinks!

As for grooves rather than rails, many tramways run in grooves because they run on city roads. Rails would be a bit of a problem for other road vehicles.

Subject: RE: Tech: How fast does a CD spin?
From: JohnInKansas
Date: 31 May 08 - 05:17 AM

The usual arrangement for tramways that I've seen is pretty much the same as at many road crossings. The "train" still runs on the top surface of a track, but the "roadway" is brought up level with the top of the rail to minimize the bump when other vehicles cross. The "groove" is just enough of a slot for the flange of the wheel to run in, but the train/tram load is still carried by the top surface of a steel rail.

There could be variants that I haven't seen; but the impression that the tram runs in a groove is a bit off from my experience.

The requirement for the flange on the railroad wheel will be quite obvious to anyone who's tried riding a bicycle down a rail - as kids in my neighborhood tried to do quite a lot (with little success, although a few kids got so they could make it 50 yards or so on a good day). [Note: modern kids aren't generally permitted such entertainment, but in case you find one trying they should be sternly warned to never try it if the track or the bicycle tire is even slightly damp. - - voice of experience!]

John

Subject: RE: Tech: How fast does a CD spin?
From: The Fooles Troupe
Date: 31 May 08 - 09:25 AM

I can definitely say that Aussie tramways WERE made with a groove - I know cause I once slid down such rails on a wet day in my car... BOOM Crunch!

Mainly only Melbourne runs any trams now - there are a couple in Adelaide, but I can't vouch for the rail shape there - it is more of light rail than a tram as I understand - but it IS a tramway. I once handled such a scrap of metal myself in a junk yard.