Talk:CD-ROM

CD sector contents

The sync pattern for Mode 1 CDs is 0xff00ffffffffffffffff00ff

Is it byte swapped? IMHO this sentance is very confusing. ECMA-130 provides following definition:

The Sync field shall consist of 12 bytes recorded in byte positions 0 to 11:
- 1 (00) byte
- 10 (FF) bytes
- 1 (00) byte

Besides it's the same for rest data modes too. And why is this line there at first place? Is it one of 2(!) main consequences extracting RAW data? Themabus (talk) 14:24, 21 December 2008 (UTC)

Optics

Why on Earth has no one mentioned the laser wavelength used to read CD-ROMs? I have added it under 'CD-ROM Drives', headed 'Laser and Optics'. Feel free to add more. —Preceding unsigned comment added by 59.91.241.35 (talk) 19:34, 21 March 2008 (UTC)

Spelling

dics are not hard to find Entry at http://www.bartleby.com/61/16/C0521600.html , and the discussion is pretty interesting.

---

FYI. Philips Electronics decided already 1972 to spell Optical Discs with a c. This was to differentiate from magnetic disks. note. the link given above is broken. Erik Schylander Kirre46 (talk) 21:12, 10 February 2014 (UTC)

Dates

Hello!! When did CDs come out? Some article...

see the compact disk page: 1982 (japan) 1983 (most other developed countries) —Preceding unsigned comment added by Jasen betts (talk • contribs) 10:01, 20 July 2008 (UTC)

I just added the year, I too was bewildered to find a page with so much detail and yet no mention of a date! CDs were introduced in 1982, CD-ROM in 1985, as far as I can tell. Playclever (talk) 23:25, 18 August 2008 (UTC)

Formats

Hi-Sierra and Joliet are top-tier formats for cd and ISO images.

Hi-Sierra and Joliet? What are they? How about the various formats of CD images, ISO, BIN etc? I am aware of these things, but not there exact meaning, so any informed addtion would be useful. Rich Farmbrough 10:04, 15 Dec 2004 (UTC)

High Serreia is the predecessor to the ISO-9660 filesystem, (there are only a few minor differences between them)!

Joliet is a Microsoft-developed an extension to the ISO-9660 filesystem which addresses filename length, directory length, and wide character (16-bit) limitations. See the following:

[1] it's so cool!

The term "ISO" generally refers to a CD-ROM image file, typically used for interim storage of CD-ROM-destined content, generally in ISO-9660 filesystem format (or one of its derivatives). ISO images are sometimes temporarily created by filesystem creation software (mkisofs on Linux), but are commonly used to transfer full CD-ROM images from computer to computer.

Other formats like Ahead Software's Nero (.nrg) formats are essentially proprietary and likely contain additional metadata and features specific to the software.

"CDROMs for the deaf?" Now thats just wrong

We need a disambuigation thing for the Recorder ID / RID, but that means that we actually need an article on the recorder ID..

(Personally, I have not heard about this attempt at big brother)

--Eptalon 22:52, 23 Mar 2005 (UTC)

Form factor

Is it just a coincidence that the CD was invented with a form factor such that their drives could be the same physical size as those of the earlier 5 1/4 floppy disks? If not, then this would mean that the inventors of the CD had it in mind all along that they might be used in PCs. Either way, there should be some discussion of this here and in the main CD article...

--4.245.5.118 23:17, 25 Apr 2005 (UTC)

It's just a happy coincidence. According to Kees A. Schouhamer Immink, the size of the CD was chosen based on the cassette tape, i.e. the CD diameter would be about the same as the cassette width. Not because there was any advantage to it, but simply because the cassette was a success. Mirror Vax 08:31, 9 May 2005 (UTC)

My understanding was that it was not just that the cassette was a success; it was a success as an in-car format. There was a requirement that it be possible to build CD players that would fit in the same space as a cassette player in a car. Jeh (talk) 09:34, 29 November 2016 (UTC)

Those magnificient bulky CD-ROMs

I see that this topic does not cover those CDROMs of yesteryears that came in special "protective" tray for each CD and could be accessed only by a special CD-ROM drive where any CD had to be inserted into a blank tray. These were initially introduced as a sturdy alternative. I just don't remember their names and can't seem to find it on the net either. So if anyone knows their name, please go ahead and include that piece of history. It's surprising that Wikipedia does not mention this and I thought most of the users around here were computer buffs.--Idleguy 14:16, July 22, 2005 (UTC)

I don't remember any CDs that had to be used with one of those drives. Rather, there were drives that required discs to be put in a "CD caddy" because they didn't have trays or regular slot loaders, and I guess some discs might have come with their own caddies. It's still a regular CD inside the caddy, though. Mr2001 16:15, 22 July 2005 (UTC)

OK. Thx. Maybe I'll add a word on that in the article. --Idleguy 05:50, July 23, 2005 (UTC)

This is interesting. I've never seen that before. Does anyone have a picture? --Mmartins 08:04, 15 August 2005 (UTC)

Simply typing cd caddy into images.google gives a view results, this one here looks nice: http://www.pc-911.com/product_images/cd_caddy.jpg

You can press the 'buttons' in the lower left and right to open it up to pickup the CD from the inside and the metal-shutter slides away like on 3.5" floppy disk, so its basically like a normal CD case crossed with a 3.5" floppy disk. Only know those things from the time where CD where single speed and a few early CD writers had them two. Heard that BluRay might use them too, however not sure about that. -- Grumbel 23:52, 18 October 2005 (UTC)

We had one of those at school in our first CDROM drive (single speed, SCSI, size of a small car, hooked up to a pizzabox 386-SX...). It seemed so awesome and futuristic :D running Encarta and having it flick into fullscreen lo-rez VGA while attempting to play the postage stamp videos. So yeah, they be real. Back in the day you wouldn't have had more than a handful of disks (Encarta was many, many times larger than the 386's hard disk, and probably rather expensive), partly because there weren't many to be had and partly because they held a comparitively large amount of info (not spamming it all away on FMV, programs that need >64mb just to load, and the like). So either quite occasionally swapping what's in your caddy, or getting two or three spares, wouldn't have been such a hardship. I remember getting our first "modern" PC, and it had a tray-load 2x drive, it seemed like a further leap into the future... what, it works just like the stereo does, it doesn't need a caddy? What's next, teleportation? Jetpacks? A modem that you can do something useful with? 193.63.174.10 (talk) 14:33, 18 November 2009 (UTC)

A quote from the article:

"...whereas caddy owners could still play loose CDs by loading them into an openable cartridge which was then inserted into the drive (this of course defeated their entire purpose and was more fiddly than loading a disc into an ordinary drive)."

I don't see the defeating-of-purpose here. Just put the CD in the caddy and leave it there forever, right? --67.172.99.160 19:44, 26 December 2005 (UTC)

Then you'd need to buy a new reusable caddy for every disc you owned...

The problem was, most people didn't buy more than the one or two caddies that came with their drive, and just swapped the disc every time. Normally, you should by a pile, and put your frequently used CD-ROMs in the caddies, leaving one or two empty caddies for all other discs. 66.114.93.6 04:03, 12 January 2007 (UTC)

I remember an early form of DVD Burner that worked like that. Seano1 18:34, 10 May 2006 (UTC)

DVD-RAM —Preceding unsigned comment added by 69.125.110.223 (talk) 21:15, 8 January 2008 (UTC)

CD-ROM size

I am confused. If 100 MB = 95.4 MiB, why is a "700MB" CD-ROM 703.1 MiB? --Byronknoll 05:39, 19 December 2005 (UTC)

I added the following text to the Capacity section: "CD capacities are always given in binary units. A "700 MB" CD has a nominal capacity of about 700 MiB. But DVD capacities are given in decimal units. A "4.7 GB" DVD has a nominal capacity of about 4.38 GiB." --Byronknoll 04:19, 30 December 2005 (UTC)

This was discussed many times in the CD-R discussion list and also on the CD-R FAQ. Actually CD-R capacity is specified not in binary units, but in time units. The first CD-R's were specified at 74 minutes of capacity, and because there are 75 frames ("sectors" if you will, but that's a different discussion) per second, a 74 minute CD-R has at least 74 x 60 x 75 = 333000 frames. There were small variations depending on the equipment used by the manufacturer (usually there was a bit more space than 333000 frames but the extra space was different between individual discs and brands). When used in mode 1, this gives 333000 x 2048 bytes = 681984000 bytes. Just like with hard disks, manufacturers like to use decimal megabyte to make the discs seem bigger so they printed "680MB" on the packaging. But in binary megabytes this is equivalent to just a little over 650MiB. Jac Goudsmit (talk) 07:14, 29 November 2016 (UTC)

For the same reason that a videotape that holds about 243 minutes of material is sold as a "four hour" one. It's easier to say/remember, and means the customer doesn't feel bilked by variations in the manufacturing process. In the early days I had a load of CDRWs of the same, cheap brand for backup purposes... QA set the various batches with permissable write speeds of 2x and 4x, and true capacities between 652~660MiB. But they were all sold as "2x, 650mb". 193.63.174.10 (talk) 14:37, 18 November 2009 (UTC)

additional: the people making the labels are both lazy, and pay poor attention to detail - i've seen all manner of sizes listed before - 680mb, 730mb, and others, all on standard 74 and 80min discs... Never mind "MiB" being pretty much something made up by wikipedia and some other people who thought the existing units (developed in an age when computer and SI terminology rarely crossed paths) were too confusing to joe average, and the best way to solve it was to make things even more complex. 77.102.101.220 (talk) 23:35, 31 January 2010 (UTC)

CD-Rom Mass Production

I often ask "How are CD-Roms made?" and people invariable answer "They are pressed!" but then cannot elaborate. Google'd the top a little but could not find much in the way of results. Can anyone add something to describe the manufacturing process?

They are more like "stamped", because the process happens pretty fast. 66.114.93.6 03:58, 12 January 2007 (UTC)

They are injection-molded polycarbonate. The mold cavity is closed, the poly is injected, and the cavity is cooled briefly before opening. In the early days, molds closed for as much as 30 seconds per disc, maybe more. Modern molding machines can spit out a disc every 3 seconds or so. [2]

cd disk

don't call it a cd-rom disk. CD already stands for compact disc

1 and 0 encoding

Regarding this sentence;

The light/dark and dark/light (pit edge) transitions are translated into 1 bits, the areas with no transitions are translated into 0 bits

Where did this come from? On what level is it supposed to be true? It might apply at the 8-14 encoding level, but it's pretty misleading in that one might read it and reasonably assume that it applied to the file information read off the disk, when in fact there are many layers of encoding between the file information and the bottom (8-14) encoding. Fourohfour 21:01, 4 April 2006 (UTC)

At the lowest level, the eight-to-fourteen modulation is based upon run length encoding of 3 to 11. No pit edges may occur closer then three clock ticks, nor greater than 11 clock ticks apart, and the channel's native frequency (4.3218MHz for CD playback at 1X speed). The EFM employs NRZI, which encodes pit-to-land and land-to-pit transitions as ones in the EFM bit pattern stream. You are correct that there are several layers of encoding and error correction on top of this foundation (CIRC, layered error correction for CD-ROM, etc).

"To put the CD-ROM's storage capacity into context ... "

The whole section describing the size of a CD-ROM in terms of novels seems unencyclopedic, and does not really add any useful information to the article. Anyone wishing to contextualize the size of a CD-Rom can do so themselves with readily available data. Furthermore, the novel example is not based on actual data (such as the actual size of the average novel) but rather on mere conjecture. The section should be removed unless it can be enhanced to add value to the article in an encyclopedic manner. 199.74.100.30 17:45, 28 April 2006 (UTC)

Perhaps you are right that the figures for the novel given should be backed up a little more strongly. However, as an example, it has a purpose. Sure, people could "work out" such stuff for themselves given the information (assuming they have reasonable intelligence), but why should they have to? We could reduce and remove lots of stuff from various articles on the basis that people could derive the omitted facts from the remaining information, but how quick or easy would this be? An encyclopedia article does not have to be dry and pared down to the bare minimum to fulfil its purpose. Fourohfour 19:30, 6 May 2006 (UTC)

I agree that information like this is indeed useful in an encyclopaedia. The 14th Britannica article on protoplasm, for example, says of a creature that it is 'about the size of a shilling-piece'; ho ho.

But I'd like to tighten it up a bit - words are not 10 letters on average, and the average novel is more than a centimetre. John Wheater 11:03, 21 February 2007 (UTC)

I think it is very appropriate to tell readers in simple vivid terms how much plain-text info a CD can hold compared to ordinary plain-text books -- to very clearly make the point that the volumetric efficiency is greater by orders of magnitude, and so is the economic/materials efficiency. The details of how this comparison is made are not important -- if anyone thinks they have a better way to make this basic point, please suggest it here for everyone to consider. -69.87.204.244 14:44, 6 March 2007 (UTC)

Speed

I think there was 16x speed too, wasnt there? I dont see it on the list, maybe someone could add it...

I (still) have a 24x, which is not on the list either. It could be that the list wasn't meant to list every speed known to man? 66.114.93.6 04:08, 12 January 2007 (UTC)

The transfer speed section has a confusion between Megabits and Mebibits. I can not correct it as I do not know if the 1x speed is 150x1000 bytes/second or 150x1024 bytes/second.

The speeds are implementation-dependent, and vary from manufacturer to manufacturer, model to model. It's largely irrelevant for CD-ROM at this point, but there have been 1X, 2X, 3X, 4X, 4.5X, 6X, 8X, 10X, 12X, 16X, 20X, 24X, 32X, 48X, 52X, and probably others (including, of course, all the partial-CAV and CAV speeds). I wouldn't bother listing all the speeds.

1X (Real-time) in CD equates to 75 sectors per second; for CD-ROM Mode 1 tracks, this is 75 sectors per second * 2048 bytes user data per sector = 153,600 bytes per second.

Indeed. I have corrected it respectively on CD-ROM, CD-R and there also was some reference to it on DVD page. ArivaldH (talk) 17:28, 24 June 2008 (UTC).

Can anyone fix the Transfer rates section so that the MB and Mb are clear? I think they are being used interchangeably, which isn't right. —Preceding unsigned comment added by 97.92.67.218 (talk) 16:50, 21 October 2008 (UTC)

Further to all this, may I draw your attention to the last part of the "Standard" section, from which I quote:

"12x drives were common in April 1997. Above 12x speed, there are problems with vibration and heat. Constant angular velocity (CAV) drives give speeds up to 20x but due to the nature of CAV the actual throughput increase over 12x is less than 20/12."

Why the heck are we still using an info statement - probably pulled verbatim from elsewhere - that appears to date from TWELVE AND A HALF YEARS AGO? When it's a fairly mainline article about a major type of media, which has undergone massive redevelopment in the intervening years? Heck, even by sometime in '98, 24x drives (aka 10-24 speed, as they baselined at 10x) had been around long enough and were common enough that I had a _spare_ one lying around, that I was able to put into a largely-salvaged P166 system in my school's upper form common room. Most systems you'll find these days will be able to break 48x, or 24 in portable drives.

I'm laying off the "being bold" in this case in case there's some _good_ reason for not updating this, but I can't think what it is unless there's been an abject failure to find any notable document that can be linked as source for the newer info. (In which case, let me put it onto a general-CD-info page on my newly upgraded-with-domain-name geocities site, and someone else can quote from and link to it ;). Does it still count as O.R. when it's easily demonstratable by anyone with a common or garden PC and a stopwatch? 193.63.174.10 (talk) 15:59, 18 November 2009 (UTC)

First computer CD-ROM

I've read in some portuguese articles that the first computer in the world to have a CD-ROM was an MSX home-computer made by Philips. This information would be very important to this article provided it is true. Could someone find more information about it? Regards Loudenvier 16:51, 12 September 2006 (UTC)

I can't answer your question - but I CAN give you some other history that you might find interesting.

I actually worked on the team at Philips Research Labs (in Redhill, Surrey UK) who produced the first ever working CD-ROM.

We took a very early Philips audio CD drive and modified it to connect up to a 68000-based 'home computer' research prototype called 'C.H.R.I.S' which we'd designed and built in-house. The first ever CD-ROM disk was pressed on the Philips audio disk production line and just 50 of them were made. The huge capacity of the CD-ROM was a bit of a challenge for us because our biggest hard drives were only 20Mbytes and the CD-ROM could hold 600Mbytes or so. We quite simply had no way to author 600Mbytes of data. Data went to the audio disk factory on VAX-formatted 9 track magnetic tape - but we needed random-access to stand a chance of getting this together. We decided that a good application to try would be a dictionary - but we quickly realised that this would be a massive data-gathering exercise - so for research purposes we decided to do just one letter (we chose 'O' - for reasons now lost to history)...it was still an insane amount of work. The idea was to have word definitions (including links much like Wikipedia's), synonyms and antonyms, images (where apppropriate) and audio samples for pronunciation.

My job as a junior engineer was to write a paint program for an artist to use to paint the pictures. Remember, this was in an era before you could buy paint software (except in specialised systems for TV production houses) - this was also before the invention of the mouse. My paint program used a digitizing tablet but I believe the demonstration system for the CD-ROM used a touch-screen.

We employed a contract artist (who'd never sat in front of a computer in his life) come in and learn how to draw using my software. He painted an Oaf (our favorite image), and Oak apple, an Oak leaf and an Oak tree...and a bunch of other things beginning with 'O'...and much, much later...an Oyster. Our office secretary (who had a very nice speaking voice and a 'posh' English accent) read out all of the words (it took her a LONG time!) and the entire team took turns to type in the text (which took FOREVER). 100% of the software was custom-written for the demo - the entire C.H.R.I.S operating system - everything. I recall that David Penna wrote the bulk of the demo software - including some nice features like antialiased fonts which were way ahead of their time. Everything was written in C.

As I recall, most of the 50 disks we pressed worked - and 50 more were later pressed with more pictures, etc. As far as I know, none of those original disks survived (what I wouldn't give to have one of those!). The system was taken to a variety of trade shows and shown off to visitors to the research labs on dozens of occasions. Eventually, the team moved on to look into 3D graphics (my part) and into CD-ROM standards and authoring tools. Originally, we anticipated software on CD-ROM being interpreted from some kind of intermediate code rather than being raw machine-code because we believed that CD-ROM 'players' would be stand-alone machines connected to TV sets that would contain a variety of CPU types. This never really took off because the PC revolution hit us and pretty much all of the cool standards we drew up were blown away in favor of the (lame) "just like an MS-DOS file system" that we're stuck with to this day.

Whilst the audio CD was a joint effort between Philips and Sony - I don't recall who put the first CD-ROM drive into a production computer. We certainly made a variety of home computers - and we did make an MSX machine - so your suggestion is quite plausible. But I really don't know for sure.

SteveBaker 20:53, 29 September 2006 (UTC)

Steve, could you add a date to this information, which I'd like to see in an article. John Wheater 10:49, 21 February 2007 (UTC)

You mean a date to when the work was done? I'm not sure precisely. We started on it before the first Philips audio CD player hit the market - but not long before - so it would have had to be 1981 or 1982 or so - but I'm not 100% sure. However, I don't think you should write an article based solely on what a fellow Wikipedian says in a Talk area. You need references that other people can check - and frankly, I don't have any or I would have written the article myself. SteveBaker 13:51, 21 February 2007 (UTC)

I too don't think I should write this article! Indeed it never crossed my mind to do so. But, ahem, I think maybe you should, some time in the next forty years or so. The thing is, your narrative is what historians call a primary source. When Niels Bohr wrote his article on the atom for the 14th Britannica, he spoke from his own knowledge; CD-ROM history is less important, but worth having on record. And firsts are an important element of history. Maybe what is needed is not an article, but a history section in this article, as a third-person detached narrative, naming those involved, citing 'personal knowledge of Steve Baker' as the reference - the sole reference if there really is nothing else, though surely the Philips records must show something. And then someone would chip in a bit of Sony history, and so we'd wiki on into the sunset... John Wheater 16:28, 21 February 2007 (UTC)

Longevity

I think it would real nice if some info about the longevity of CD-ROM for long term archiving is included in the article : Jebrennan 03:27, 7 December 2006 (UTC)

It's a fairly controversial subject. Some CD's (not really CD-ROMs necessarily) were made with some kind of cheaper aluminium layer. If there was even the tiniest pinhole in the layer of aluminium, it would slowly grow by a weird process something akin to surface-tension in liquids) until it covered enough area to cause a mis-read. If there were sufficiently few of them, the CD's error correction processing would repair the data stream - but this only works if the hole doesn't grow too big - if the holes are not positioned fortuitously - and if there are not also too many surface scratches. Eventually there are too many errors and the error correction system would be overwhelmed.

But it's hard to place a definite lifetime on the CD because so much depends on where the holes are - how old the disk is - and how much usage it has had. I've had disks from that era fail in less than a year. Once the problem became really well known, most of the fabrication plants tweaked their processes to eliminate the problem - so I doubt that modern CD's suffer from the problem. Aside from that issue, a CD that's left in storage in a dark place - propped up on it's side and supported by the center hole - should have an enormously long shelf life. I don't think an upper limit has ever been established. The very first audio CDs I ever bought still play just fine (Dire Straits "Brothers in Arms", some Glen Miller and some Bach fugues), Those were bought on the first day that consumer CD players and disks went on sale - only to Philips employees and only in our "Staff Shop"). Those are probably amongst the oldest mass-produced consumer-grade CD's in existance and they still play just fine.

Recordable disks are a different matter - they work totally differently from mass-produced disks - I have no idea how long they might be expected to last.

SteveBaker 23:36, 28 January 2007 (UTC)

Personal account: It's highly variable and dependent both on manufacturing and storage. I have been tooling about with disc burning for neeeearly 10 years now (first burner Xmas '99). My first ever disk, on the quite high quality sample disk included with the burner (yes - it was THAT novel at the time, that they had to include samples in case you couldn't buy blanks straight away or were just THAT eager to try it... like I was!) still survives. Other disks burnt at various points in between show a mix of survival, failure, and heading towards it. Even some that are only a couple months old have poor readability if burnt badly, on cheap media, or left in the sun. I try to only use good quality blanks these days as I write far less disks that I used to. It's not worth the risk. A great many MP3 backups that I wrote over the years - overburnt out to 713mb on cheap media, because I couldn't afford to upgrade my hard disk - have serious amounts of unreadable files. Being kept 2-up in slim cases, themselves 2-up, in an open rack facing a window that catches the morning sun hasn't helped, either. The "archival quality" claims of the expensive types, if they are burnt at low speed, and kept in a dark, constant moderate-to-low temperature, low humidity environment in sympathetic cases, are probably closer to truth than lie (though who's going to sue if they don't meet the "200 year" claim?). Everyday use of optical media - particularly affordable optical media - rarely meets these standards, however.

The worst examples I've seen of disk degradation, however, match with the example above. It's literal "disk rot". Many cheap CDRWs I bought as multiple-generation rolling backup media eventually succumbed to it... probably because they had dull grey Alumin(i)um backing to their phase-change layer. At some point, a little pinhole appears... and poof... your data at (and largely after, as they were "image" backups) that point has gone. At one time I had piles of these things, each with a little marker-pen note saying whether it was "all OK", or to what capacity it could be safely written, ie where the hole was. They seemed to get slowly worse over time, so the holes must have been growing. I've also got a few pressed audio CDs that are succumbing to rather bad examples of rot from the outside edges in (poor sealing). They are all mid 80s or early 90s releases - oddly, two by Bon Jovi (and another by Aerosmith). Therefore it's going to be a while before they become unplayable, as they were transferred from LP and only about 2/3rds of the maximum capacity is used.

An interesting case of CDR fade in action though is a pair of some pale green (or at least, they're NOW pale green) generic type I burnt a double compilation of music onto. A CDROM drive and PC disk will just start throwing CRC errors and you won't get much idea of what's going on other than it's broken. These ones however... they really send the audio error correction hardware into overdrive. Very little skipping, but, oh, the noise level and the crackling. It fades in and out, and at times sounds like a poorly tuned AM station that's somehow in stereo. The pretend pit / land record must be literally fading away to the point where it can't be detected at all in places, and the hifi has to fudge the signal to cover it (amazing it was still able to track, in fact). Imagine that happening to your data - and to it's error correction code, too. There's only so much fuzz that can be tuned out by ECC. And this after only... I think it was something like 7 years? I've got audio cassettes and VHS tapes 3 or even 4 times older than that which still work fine (indeed, a hard disk that's almost 3x that still works), and vinyls that are much much older still that sound good. The disks weren't abused, they may have lain in the sun once or twice, but... they had full labelling over the top edge, and tended to live in a black-backed mini case (one each) with an opaque inlay over them, limiting their exposure. It's just not a reliable medium, if you don't invest in top notch disks.

(OTOH some really cheap crappy ones have survived a-ok, and one or two major-seeming brands - that i won't touch any more - die quickly. The moving and shaking behind the scenes in disk-fab-land is a murky business. All you can really do is try to improve your chances, rather than getting a guarantee. Best you can do is print your archival stuff with carbon pigment onto acid-free paper and put it in a fire safe. Buried inside the tip of everest.) 193.63.174.10 (talk) 15:44, 18 November 2009 (UTC)

I'm glad to find some information about lifespan in this Talk section, but how come it doesn't seem to have any mention in the main article? From my own (poor) attempt in trying to research how to find out how to back up my computer, it sounds like HDDs, DVDs, and CDs all are extremely failure-prone and that you can't actually ever back anything up without printing it out to paper. The DVD and Hard disk failure articles both mention different numbers and sources for lifespans, and I'm just really confused if it's even possible to rely on technology at all for things like family photos (at least without having to spend a lot of money to make dozens of copies over and over again)...I hope the reliability of storage can actually catch up to the fast-increasing capacity and that some research organization will find some definite numbers on which consumers can rely. Zeniff 21:47, 14 May 2010 (UTC) —Preceding unsigned comment added by ZeniffMartineau (talk • contribs)

File Name Length

When burning a CD, the CD format seems to limit the length of file names. If someone knows the rules, it would be great to have it here. Also, there seems to be a limit to the number of characters in the title of a CD too. Thanks. Jebrennan 03:27, 7 December 2006 (UTC)

No need to clutter up the CD-ROM article with that kind of information, while it is available in the correct articles: Universal Disk Format, ISO 9660, Joliet (file system). Note that there's no such thing as a "CD format", but in fact more than one CD-ROM file system.

On a personal note, if you feel the file naming is too limited for your purposes, I'd suggest you use a better CD/DVD authoring software that supports UDF (IMHO, ISO9660 and Joliet are outdated and should only be used when you have to -> on old players or operating system.)--87.122.52.27 16:43, 23 January 2007 (UTC)

When was the first cd rom produced? What about the history of adoption of the format?

Trollderella 08:13, 14 December 2006 (UTC)

Scroll up a bit and read my comments under "First computer CD-ROM" - I actually worked in the group who produced the first ever CD-ROM. Sadly, I can't write about it for the article because that would be OR. SteveBaker 23:11, 28 January 2007 (UTC)

Read-only "media"

Resolved

 – Removed

“ It is also debated whether the correct terminology is read-only memory or media. It is generally accepted that, in technical terms, media is the correct terminology. However, due to the widespread use of ROM to refer to other devices such as EEPROM and Flash-ROM (where memory is the correct terminology) most people define CD-ROM as also being memory as it sounds like the abbreviation is from the same origin. ”

I have removed this unreferenced and rather weaselly and spurious assertion (and other mentions of it) from the article. Plugging the term "compact disc read-only media" into Google returns a piffling 72 unique results, compared to 232,000 for "...memory". This suggests the "media" interpretation of the acronym is far from "generally accepted". FOLDOC, OED and Webster's all agree "memory" is the correct term. ~Matticus ^T_C 20:16, 28 January 2007 (UTC)

(As I've said previously - I worked on the team that made the first CD-ROM). The term 'ROM' - meaning "Read Only Memory" was in common use a decade before we came up with the CD-ROM. There were already lots of kinds of ROM - 'PROM', 'EPROM', etc. The name 'CD-ROM' came about in the obvious way - from taking the name of the audio disk "CD" and tacking on "ROM". So it's definitely 'Memory' and not 'Media'. SteveBaker 23:18, 28 January 2007 (UTC)

Like many things, popular acceptance has asserted one over the other, so the number of links on Google isn't really a valid measure of 'correctness' in this sense (especially as the Google algorithm will naturally lean towards the currently indexed pages). I do however accept Steve Baker's comment and defer to his closer knowledge on this subject. Having said that, I worked in PC hardware when the CD-ROM was released and had an intimate knowledge of the market and the coverage in press. Whilst most of those paper-based arcticles have no on-line archives going back that many years (there is no call for them), I do not think it valid to ignore the large number of people who, at the time, believed (rightly or wrongly) that 'media' was the more correct definition. I did endeavour to reference my original statement, but as already pointed out, widespread use of the 'memory' acronym has rendered the 'media' use somewhat outdated. As you will notice, Steve also agrees with my statement that the reason the 'memory' was chosen/accepted was because of the widespread existing use of other 'ROMs'. My proposal is to rewrite my original statement in a more 'neutral' manner indicating that the debate is now somewhat moot because of the general acceptance of 'memory'. This should ensure it is not open to being interpreted as weaselly. Please enter comments on the subject here and I will endeavour to post at some point in the next few days. DanMatthewsUK 12:48, 16 February 2007 (UTC)

Duly amended as per my statement above. DanMatthewsUK

I was about to bring that up when I saw this. I can still see problems with it. For a start it is entirely unsourced - just who says that precisely? Secondly it does not strike me as even being correct. If you were going to argue along this line the correct term would be compact disc read-only medium - i.e. the singular term. However even then I doubt its validity. Historically memory has always referred a broad spectrum of devices, not merely random-access technologies - if that was not the case the very term "RAM" would be superflous. In the absence of a reliable cite I suggest that entire point should be snipped since it strikes me as someone with an axe to grind rather than a real point. CrispMuncher (talk) 19:18, 26 January 2010 (UTC)

I was about to say exactly the same thing on reading that paragraph. "Memory" can refer to any storage device - modern usage to refer to main memory (RAM) does not alter that. Since it is obviously still problematic and still has no source backing it up I'll remove that paragraph completely. Minority Carrier (talk) 16:05, 31 August 2010 (UTC)

I don't understand the line of argument for not having the "media-section" included. First of all, I see Wikipedia as a source of knowledge. A section about this discussion, that is short, consise, and does not interfere with the rest of the article, will only add to the knowledge provided, not confuse it! Even if the term is wrong, it has still been used, or at least suggested. Secondly, it is argued that memory may refer to "any storage device", thus also a CD-RO?. Yet, you don't buy a computer with 4 GB of random-access-memory and 500 GB of harddrive-memory. Likewise, I've never heard anybody state that they have a bookshelf full of book-roms, each with 500 pages of memory, although that could be a technically correct term. In computing, storage and "memory" are usually considered different entities, even if a general definition of memory may cover them both. I see CD-ROMs as storage MEDIA, and consequently don't think the term "memory" is appropriate, as in the case of "harddrive-memory", or plain old fashioned book-roms.

Judging from Steve Baker's comment, the term was coined more as a "catch-phrase" in a time where many types of ROM were widely used (Regular ROM's, PROM's, EPROM's, and later, I guess, EEPROM's). Since this is the case, I fully accept that "Compact-Disc Read-Only-Memory" is the original, intended, and in that sense correct term. But I don't see any reason to neglect the fact, that in "common computer language" the term is misleading, which has caused debate of the CD-ROM acronym. This brings me back to the first argument, that wikipedia is a source of knowledge, which should be restricted by personal preferences! Jacobmelgaard (talk) 06:38, 11 October 2010 (UTC)

The naming section would have some traction if there was any source for it. This has been under discussion for over three years and none has been forthcoming. Without that is it little more than a rant by a random editor of the opinion that the acronym is somehow inaccurate. The argument about book-roms etc is nothing more than a straw man - the meanign is clear from context. Yes, early hard drives were referred to as memories: it is onyl with mdoern usage that the term has fallen out of favour. That does not make it any less correct. Minority Carrier (talk) 04:47, 16 October 2010 (UTC)

How is the rate of 150 kB/s calculated?

How is the 1x rate of 150 kilobytes pre second calculated? Is the unit SI base 1,000 or base 1,024? —Dispenser 01:18, 19 February 2007 (UTC)

It is 150 KiB per second. It is described on Red Book standard page and on CD-ROM page (yes. As of Today (24 Jun 2008) it is. ArivaldH (talk) 17:26, 24 June 2008 (UTC)

If so, the article has many errors in it. —Preceding unsigned comment added by 71.167.65.179 (talk) 03:17, 14 October 2009 (UTC)

"By comparison, the bit rate of a "1x" data CD is defined as 2048 bytes per sector × 75 sectors per second = 150 KiB/s, or approximately 9.2 million bytes per minute."

To clarify - it's exactly 153,600 mode-2 user bytes per second. 176,400 for audio, 175,200 for mode-1, and 183,750 overall system bytes when you consider the error correction (or mode-1, audio...), subcode, etc. Convert these to your chosen units as you will. 77.102.101.220 (talk) 23:47, 31 January 2010 (UTC)

recording at high speed

"Recording data CDs at very high speed (40x) can be done without losing information. However, if done the same with PlayStation or Audio CD it will result in an unreadable PlayStation disc or an audio CD with lots of clicks because there are no error correction codes and the errors are more likely to occur at high speed recording."

After the first sentence, this paragraph from the current article sounds kind of stupid. It should be deleted or re-written by someone who knows what they are talking about and knows how to write well. -69.87.204.244 14:31, 6 March 2007 (UTC)

slot loading drives and 80mm discs

The article states that slot loading drives have troble accepting 80mm CD-ROMs and that the Nintendo Wii has overcome this problem however recently on my Imac G3 slot loading (2001) I was recently able to use an 80mm disc in it perfectly.

CD-ROM SIZE RELEASE DATES

http://en.wikipedia.org/wiki/Floppy_disk

FLOPPY DISKS PAGE TELLS THE YEAR FOR EACH SIZE FLOPPY DISK THAT CAME OUT. WHY NOT CDS? —Preceding unsigned comment added by 24.188.17.249 (talk) 22:28, 28 September 2007 (UTC)

POSSIBLY BECAUSE CDS ONL... ahem, excuse me. Because CDs only come in one main size, and there's probably no clear data on when the 8cm ones (which are essentially just part-recorded 12cm discs, cut down) arrived. By contrast each different type of floppy was basically an entirely new kind of media, from the perspective of formatting, having to have entirely new case designs, and moreover new drives built in order to be able to use them. The difference between a consumer-level 3.5" DSHD 1.4mb floppy and the original 90-ish kb, 8" type made by IBM for its mainframes is immense, and it's only by happy accident you'd ever find a way to read an 8" in a home PC (it can be done, but it's a right bodge and needs particular chipsets, plus a salvaged minicomputer/early micro drive). Whereas the differences between a 210mb 8cm CD, a 12cm one that's merely been burnt to 210mb, or full-up 12cms of 530, 650, 703 and 790mb capacity (63, 74, 80, 90 minute) is trifling and mostly one of trivial set-up detail. Even the difference between a 63 min CD and a DL DVD can be likened to that between a single sided, single/double density drive and a double sided high density one of the same size (5.25 or 3.5")... but in that case, we have release dates for "CD" and "DVD" as discrete classes of 12cm optical disk, and there were no in-between formats such as SSDD/DSDD. The newer drive in both cases will read the disks originally made for the older one, too... The jump from, say, 5.25 inch to 3.5 inch is more like going from CD to Hi-MD. 193.63.174.10 (talk) 15:03, 18 November 2009 (UTC)

DVD to CD size

4.38 / (700/1024) = 6.4

Not that difficult... —Preceding unsigned comment added by Craigblock (talk • contribs) 19:54, 15 January 2008 (UTC)

It says 4.4 GiB, not GB. That is gibibits, not gigabytes. A CD holds 747 MiB (mibibits) or 700 MB (megabytes). 4.4 GiB / 747 MiB = 5.89 (or roughly 6). You are correct, it isn't that difficult, but only if you use the right terms. There are other mistakes in the article where it shows 700 MiB that need fixing as well. I reverted back. Pharmboy (talk) 20:07, 15 January 2008 (UTC)

There's a error on that, which might explain the under 6 result. 700 MB is 734,003,200 bytes (700*1024*1024). And secondly, MiB should be mibibytes, not bits. 85.217.14.225 (talk) 10:00, 3 November 2010 (UTC)

A CD holds 700 * 1024^2 bytes. A DVD holds around 4485 * 1024^2 bytes. 4485/700 = 6.4. A DVD holds 6.4 times the amount of checksummed data as a CD. —Preceding unsigned comment added by Craigblock (talk • contribs) 23:14, 15 January 2008 (UTC)

What the hell, people. Let me break this down for you before we get hung up on mebi-bibble-bytes and whatever. Using the same units for both...

Large type of DVD recordable ("minus") vs 74 minute CD: 4488 "MiB" vs 652. 6.88x larger.

Smaller type of DVD recordable ("plus") vs 80 minute CD: 4483 vs 703. 6.37x larger.

Figures arrived at by empirical means, I'm afraid, but I think O.R. is probably acceptable for reasons of discussion?

I don't know the hard limit for storage on a single-layer pressed DVD but we can probably assume it to be similar. Somewhere between 6.3 (rounding down because overburning is entirely usable on a CD but a bad idea for DVD - i've found 710 and ~4400 MiB to be acceptable limits of reliability) and 6.9x that of a CD, depending which particular varieties of apple and orange you're choosing to compare. Call it 6.6x if you want a single easy figure. Was that so hard?

Personally if splitting archive files for portability I'll bring down the axe at 640 MiB, which is a bit of a waste with 80-minute CDRs but means you can also put 7 of them onto a DVDR at once (4480 MiB, fitting pretty much any blank out there... bit of a risk of errors in the last 80mb, but if it's for short term file transfer use and burnt at 8x or less the data usually survives).

Dual layer disks and DVD-RAMs are an entirely different matter. The only DLs I've used were 8152MiB (not quiiiiite 8.0GiB, probably for filesystem reasons as much as anything). Giving us 11.6 to 12.5x that of a CDR. You'll likely want to settle for 12x (and 12x 640 MiB, at that) though, given how goddamn unreliable they are. RAMs, I have no idea, it's officially "3.8gb", which probably equates to ~3624 MiB in practice, or ~5.3x CD. (Or 6.5x a 63-minute mastering CD).

That good enough for you? 193.63.174.10 (talk) 15:16, 18 November 2009 (UTC)

technical specs

Removed the following from the Bit article, in the "storage" section:

“On storage devices like 1,200,000 nm-thick CD-ROMs, a bit is mechanically etched by intensive laser beam as a pit about 168 nm deep and 670 nm wide of variable length (depending on data type) on concentric tracks spaced 1,600nm apart. The total length of the track in a 650 MB disk thus may span several kilometres. The light of the reading laser is reflected back into the laser, which then picks up that light with a sensor. The transition between a pit and a ground means a 1, and a short period of time on the same level is a 0. No more than 11 consequent zeros may occur, because the laser receives no state change during consequent zeros and has to rely on a timer to know the amount of zeros, whose accuracy is limited. CD-Rs work on the same theory, except that they use dyes instead of pits and ground.”

Notice how the numbers differ from those in Compact Disc#Physical details. This stuff here may be of interest.
--Jerome Potts (talk) 04:46, 4 October 2008 (UTC)

References

Untitled text moved from above table of contents

15:25, 4 October 2009 (UTC) Will someone please tell me if you can create a 'read only' CD which then allows the next used of the CD to be kept from changing anything on the original CD? Like if there is a letter copied onto the first CD, can it be entered and changed by someone else later if it is supposed to be 'read only??' thanks! oct 4, 2009. —Preceding unsigned comment added by 76.190.253.227 (talk) 15:25, 4 October 2009 (UTC)

Weeeelllll you've got a few options. First one, if you can stand the massive inconvenience and cost of not being able to change ANYTHING on your 10-cent disc after making it, is just to put the files onto a vanilla, write-once CDR... nothing short of actually damaging the disc will then be able to alter anything, and said alteration is better described as "destruction". If for some wierd reason this isn't possible you could just try making the file itself have "read only" properties (though this is generally only a minor irritation to human users, who can hit the "are you sure" button or turn the attribute off - it's only really effective against programs) either before or after th burn depending on whether you're doing CDRW/multisession CDR or using a packetCD. More effectively you could look into some digital signature/encryption/etc software that will properly secure the file against unauthorised changes, or even reading/access. This will likely cost you quite a bit more than a few extra throwaway CDRs, however. As a final note, I see you can now buy a drive which has built-in data protection and security features... this might be of interest also. Good luck. 193.63.174.10 (talk) 14:13, 18 November 2009 (UTC)

DDDUUUUUUHHHHHHHHH

you guys should atlest mention who made it DDDDDDDDDUUUUUUUUUUHHHHHHHHHHHHHHH... IN THE FIRST PARAGRAPH. AND ACTUALLY SAY THE CD ROM WAS CREATED BY.... BECAUSE NOBODY EVER SAYS WHO —Preceding unsigned comment added by 209.26.59.205 (talk) 16:23, 24 January 2009 (UTC)

== كنت عايزاعرف الفرق بين السى دى روم والسى دى ريتر

==

'''Bold text'''

محمود    mhmoud_202016@yahoo.com

You guys are awesome, without true genuine winners like yourself, civilization would simply fall apart. I believe there's a personal account somewhere up above from one of the guys on the original Phillips CDROM prototype team? 193.63.174.10 (talk) 15:21, 18 November 2009 (UTC)

OK to be more fair to Mahmoud there... looks like you're after the difference between cdrom and cd writer... well... maybe you're having as much difficulty getting hold of an understandable arabic version as I am an english translation of what you said (one significant word remains obscure). So, let's try to put it in simple language. CD ROM = disc is made in a factory, the data is chosen by someone else and cannot be changed. CD writer is a device you use to create your own CDR and CDRW discs. Alright? :) 77.102.101.220 (talk) 00:02, 1 February 2010 (UTC)

Transfer rate section is in disarray

The section on transfer rate is pretty messed up. I'm not even sure it's self-consistent. Here is my understanding: A 1x transfer rate corresponds to a track speed of 1.2 m/s at all positions on the disc, which corresponds to an angular velocity of 500 rpm at the inner diameter and 200 rpm at the outer diameter. These numbers scale for speeds up to about 12x, I think. Above 12x, drives typically operate in a constant angular velocity mode (constant rpm) so that the drive isn't forced to ramp the motor speed up and down as the head seeks to different positions. In CAV mode, the "x" value refers only to the transfer rate at the outer edge of the disc. At the inner edge the transfer rate is about 2.5 times lower. Thus, a 52x drive spins at 52x200rpm = 10400rpm. Period. Not "up to 26000" as the article now states. And the track speed at the OD is 52*1.2m/s = 63m/s. Period. Not "65 to 163 m/s". I don't have references handy; unless someone gets to it first, I'll at least remove the unreferenced stuff that I know to be wrong. Spiel496 (talk) 05:02, 21 March 2010 (UTC)

Mode 2 Form 1/2 is missing

It would be nice if the 2 different sector formats are described here, incl. why Mode 1 is more common today than Mode 2 Form 1. --RokerHRO (talk) 20:24, 23 January 2012 (UTC)

Unclear scope / overlap with Compact disc and other related articles

The scope of this article is unclear. It sometimes goes beyond the CD-ROM, properly speaking. In particular, this can be seen in the Transfer rates and Copyright issues sections. The CD-ROM is just one of the CD types discussed in these. These sections discuss all types of data CDs.

It seems we don't have a consistent scope in the article. The scope may be CD-ROM-s everywhere, but in different senses. Sometimes in the strict sense, sometimes in the sense of data CD, read-only or not. It is understandable that this article discusses data CDs, as the CD-ROM was the first form of (general) data CD, but I'm thinking it's probably best to move most discussion on data CDs in general to Compact disc. Otherwise, if we keep using "CD-ROM" in the sense of data CD, we need to make that sense clear in the lead. --Chealer (talk) 15:10, 9 March 2013 (UTC)

512 byte sector size for older Sun and DEC machines

Should the article mention that early CD-ROM drives for Sun and DEC machines (and maybe other Unix flavour machines) used a 512 byte sector rather than the PC / MSDOS 2048byte sector. This required special versions of the CD-ROM drives (typically with SCSI interface), see:

http://sites.inka.de/pcde/help/dec-cdrom-list.txt http://www.pimpworks.org/sun/backgrnd.html

John a s (talk) 19:08, 22 April 2014 (UTC)

What format is the address given in? I've got lots of questions on this.

Does it specify the byte number of the first byte of the sector, or the mm:ss:ff time code? Does it specify the address at the start of the header of that sector (the first byte of the sync pattern of the header of the sector), or does it specify the address at the start of the data section of the sector, or does it specify the address of the first byte of the address field (in other words, the address field specifies its own address)? Is it a big-endian number, or a little-endian number? — Preceding unsigned comment added by Benhut1 (talk • contribs) 00:44, 3 May 2014 (UTC)

3234 Bytes?

Sorry, but isn't a sector 3234 Bytes? Why can't I find that number on the whole page? — Preceding unsigned comment added by 93.232.209.201 (talk) 18:08, 16 May 2017 (UTC)

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Speed Table

It would be helpful is there was an additional column specifying when drives of the various speeds were made available. I came to this article looking for exactly this.

I also own both an NEC 3x and 6x speed drives, which aren't represented in the able, at all. Valgrus Thunderaxe (talk) 01:21, 3 August 2022 (UTC)