CD-ROM, CD-R, CD-RW, Books of Red, Blue, Purple, Beige, Orange, Scarlet…

CD-ROM, CD-R, CD-RW, Books of Red, Blue, Purple, Beige, Orange, Scarlet…

December 11, 2019 100 By Kailee Schamberger


If you look at a blank CD-R, odds are you’ll
find these two numbers. 80 minutes of audio, and 700 megabytes of
data. You may be surprised to learn that these two
numbers don’t match. See, let’s take the 80 minute figure. We know that the Compact Disc Digital Audio
standard consists of 2 16 bit streams (2 because it’s stereo audio) each consisting of 44,100 samples per second. Let’s make it a bit easier and say that
it’s one stream of 8 bit words or bytes, so by doubling 44,100 twice (once for stereo,
once again to turn 16 bits into 8), we find that it’s 176,400 bytes per second. Multiply that figure by 60 for sixty seconds
per minute, and again by 80 for our eighty minute runtime, and you get… 846,720,000 bytes. It would seem that an audio CD holds over
146 more megabytes than a data CD. What gives? We interrupt this program for a marginally
important message. In the computing world there is an unfortunate
mixing of the terms megabyte and mebibyte. You’ll almost never hear someone say mebibyte,
because it’s a silly word, but the 700 on this disc is actually referencing mebibytes. What’s the difference? A Megabyte is 1,000,000 bytes, based on powers
of 10. A mebibyte is based on powers of 2, so it
is actually 2 to the 20th bytes. So, a kibibyte is 1,024 bytes (rather than
1,000) and a mebibyte is 1,024 kibibytes. This annoying debacle has been causing problems
forever, for example hard drive manufacturers quote sizes in gigabytes or terabytes, when
your PC works in terms of gibibytes and tebibytes. So this 2 terabyte portable drive only appears
as 1.81 terabytes on my PC. But my PC is actually misrepresenting this
figure as terabytes when it is in fact tebibytes. But CDs and DVDs are quoted in mebibytes and
gibibytes, so even though this label shows MB instead of the correct M lowercase i B,
my computer does the same mislabeling, and since they’re both wrong, they agree. Anyway, all of this is to say, I’ll be using
the word Megabyte, even though sometimes it’s actually a mebibyte. Please send complaints to: It would seem that an audio CD holds over
146 more megabytes than a data CD. What gives? Well it’s actually more of a “what takes
away” as the CD-ROM standard sacrifices those bytes for more precise error correction. As discussed in this channel’s first video
on the compact disc, the CIRC error correction used in the Compact Disc Digital Audio standard
can perfectly correct errors up to 3,500 bits long. But, it can also mask errors up to 12,000
bits long through interpolation. That means that it’s essentially guessing
what the audio samples should be for errors between 3,500 bits and 12,000 bits. Now, for audio samples, that’s fine. 12,000 bits is less than one one hundredth
of a second of audio, so even though the error correction might be fudging things, you’ll
almost certainly not notice it. But for data, that’s not gonna do it. Data cannot be fudged without serious consequences. In order for the compact disc to store data
files reliably, it would either need to sacrifice durability or come up with a new error correction
scheme. And it did neither. But also yes. CD-ROMs (or would that be CDs-ROM?) use the same CIRC error correction and basic data structure of the CD-Audio disc, including
the frame structure, subcode, and all that. But more error correction was added within
the frame (which we’ve now formally decided to call a sector). Of the 2,352 bytes available in a sector on
an audio CD, 304 get sacrificed, mostly for error correction, but also for some basic
signalling, such as synchronization and distinguishing between mode 1 and mode 2. Combined with an additional layer of CIRC
error correction, the CD-ROM standard maintained the same durability with zero tolerance error
correction. We’ll get to Mode 2 later, but nearly all
CD-Data applications use Mode 1 for its complete error correction. Now that the compact disc was being used for
more than a simple linear stream of audio, a true file system needed to be standardized. Initially things were rather ad-hoc, but a
group of 12 computer hardware manufacturers met at what was then the High Sierra Hotel
and Casino in Lake Tahoe, CA, where they settled on a standard called the High Sierra Format. Eventually this would become ISO 9660, the
standard used to this day, however it has been extended and improved over the years. Now that the CD-ROM was officially a thing,
whole new multimedia experiences could be created. With the ability to store images, program
files, sounds and even video, the possibilities with CD-ROM were seemingly limitless. No longer bound by the 1.44 megabytes of a
3.5 inch floppy, elaborate games with full-on soundtracks, thousands of color images, and
more complicated structure could be produced. My greatest nostalgia factor comes from mid-nineties
educational games, like the Magic School Bus games or my personal favorite, JumpStart 3rd
grade. Seriously, this was a wicked awesome game
and it’s holding up pretty well I’d say. [In another day, the world will see the dawning
of Polly Planet.] *buzz sound* [Whoops!] [It seems there’s someone at the door.] [Let’s take a little peek!] Anyway, of course home computers weren’t
the only beneficiaries of this sort of vast data store. Video game consoles soon appeared which could
take advantage of it, in fact one of the earliest was the Philips CD-i system. It technically wasn’t using CD-ROMs, though,
as CD-i discs were in fact their very own category, published in the Green Book. But unless you’re either very young or were
living under a rock through the 1990’s and early 2000’s, I’m sure you already knew
what CD-ROMs could do. But the OM, in that CD-ROM, man that’s a
bummer. Sure, having 700 megabytes at your disposal
is fantastic, but no one has a CD manufacturing and duplication facility just at home. But wait, they do! The development of the CD-R, for Compact Disc
Recordable, meant that no longer would you be forced to write up a contract with a commercial
CD pressing facility for at least 10,000 discs just to make a mixtape, instead all you needed
was a $35,000 machine and a computer! It would take until the mid-to-late 90’s
for CD burners to come down in price, and even then there were annoyances, but now we’re really talking. A CD-R, which incidentally is a pirate’s
favorite kind of CD, is constructed much the same as a normal CD, but with two important
changes. First, the pits and lands molded into the
polycarbonate layer are replaced with a continuous spiral pregroove. This spiral will guide the laser of a drive
writing to a disc, and it also contains the ATIP which tells the drive the properties
of the disc, such as its maximum write speed. Right on top of the pregroove is a thin layer
of an organic dye. That’s why CD-Rs are sometimes a strange
color, or even just a little bit off from the normal silver. Then on top of the dye, a partially transparent
thin layer of metal, usually aluminum, is placed. This allows the laser light to be reflected
back while still being influenced by the dye. To burn data on the disc, the laser switches
from it’s everyday gentle glow to an all-out LIGHT CANNON of FIRE LASER, and the high intensity
heats up the dye so much that its optical properties change. That’s right, CD burners are literally burning
the equivalent of pits onto the disc. Once it’s been written, almost any CD drive,
going back to the earliest CD players, can read these discs. The parts of the dye that were made into a
“pit” by the writing laser will dim the reading laser’s reflection, which is much
the same as how real pits cause destructive interference. So long as the CD reader can tell the difference
between a burned spot and an untouched spot, it will read the data just fine. Being able to store data files onto a compact
disc at home meant that just one of these guys could replace hundreds of floppy disks. But now we had a new problem. Remember how in a normal CD, there are three
parts? The Lead-in, program area, and lead-out? Well, if we stuck to this limitation for the
CD-R, then if you were to write as little as a Word document on a blank CD, you’ll
have written the lead-out, and now the disc is done. The Orange Book introduced the standard of
multi-session writing. Now, after the lead-out of the disc, another
lead-in can be made. Each time a new session is made, the lead-in
is updated to include the location of all the files. On a multi-session disc, the drive will look
for all of the lead-ins, and once it finds the last one, it basically just ignores the
rest. This is also how a file can be “deleted”
from a CD-R, as the latest lead-in may simply not include it in the table of contents. But the data is still physically there, and
there are ways of getting to it. Of course, the central limitation to the CD-R
is that is a write-once, read many format. In fact, its original name was going to be
CD-Write Once, which I really wish had been stuck with because we could have called them
CD-WOs! Woah! But, we wouldn’t be stuck with write-only
for long. Interestingly, the Orange Book detailed a
rewritable CD based on magneto-optical technology in 1990 (the technology behind the MiniDisc). This never made it to commercial production,
but the CD-MO would have been the perfect companion to the CD-WO. Instead, we got the CD-RW in 1997. This is functionally identical to a CD-R,
but the organic dye layer is replaced with a Silver-Indium-Antimony-Tellurium alloy,
also called by at least one person AgInSbTe. This alloy has a unique property which alters
its reflectivity based on phase changes. In an unburned disc, the alloy is in a polycrystalline
structure. But when the laser heats it to somewhere in
the neighborhood of 500-700 degrees C, it melts it. And when it solidifies, it no longer has the
same crystalline structure, and thus it reflects light about 15-25% less intensely than the crystalline
parts. So, spots that are melted by the laser turn
into sorta pits, and spots that aren’t remain sorta lands. What allows the disc to be re-written is that
when the alloy is heated to around 200 degrees C, it doesn’t melt, but any parts that have
lost their polycrystalline structure will actually reform. This effectively erases all of the burned
pits, and allows the disc to be written again. CD-RWs have several severe limitations, though. Unlike a CD-R, these discs generally cannot
be read in standard drives. Because the change in reflectivity between
a pit and land is so slight, a CD reader needs to be much more sensitive to pick up the data. After the introduction of the CD-RW, many
standard CD readers were made more sensitive to accommodate them, sometimes branded as
Multi-Read, but it certainly wasn’t universal. Another big problem of the CD-RW was that
the discs weren’t always backwards compatible. Because of that phase-changing alloy, there
is actually a minimum speed to write the disc. This basic 1-4X disc will work in pretty much
any drive, so long as you can force it to burn slowly, but later, higher-speed discs
might need a minimum speed of 8x or more, so if you only had a 4x drive, you’re SOL. And before we put the CD to rest, let’s
look at some of the other stuff that those crafty engineers at Sony and Philips jammed
into here. Remember the subcode channels R through W? Eventually these would get used. CD+G, for CD Graphics, was used in karaoke
machines. The first CD+G discs were released in 1985. This was further refined into the CD+EG, standing
for Extended Graphics. In what seems backwards, it would take 11
years for Sony to introduce the CD Text format, in 1996. Also using the R through W subcode channels,
this was essentially a way to add metadata such as track titles, artists, album, and
all that jazz. Oddly, I can’t find references to it being
used for lyrics, which seems a wasted opportunity as there definitely is room. Remember the Mode 2 in CD-ROM I talked about
earlier? That’s right, I’m putting it in the same
video this time. CD-ROM Mode 2 sacrificed some of the error
correction of mode 1 for a larger data capacity, about 800 megabytes. You wouldn’t want a computer program or
documents stored in Mode 2, but for things like video files or large collections of images
where a small error will simply result in a glitch or artifact, it was OK to use. Video CDs, defined in the White book, used
Mode 2, and now that I know that, VCDs make a lot more sense to me. The video compression of VCD is ridiculous,
but knowing that it’s actually playing with 800 megabytes makes it seem a little less
crazy. And there were other odds and ends. The delightful beige book defined a standard
for photo CDs in 1992. The standard was a little ahead of its time
though, as in 1992 CD-ROM drives really weren’t that common yet, and it also stored photos
in a proprietary format. Kodak developed the Photo CD in a time when
digital cameras weren’t really a thing at all for consumers, so in a sense it was a
very clever product. Get your film developed and receive a disc
with very high-resolution scans for future use. But by the time CD-ROM drives became widespread,
digital cameras were starting to appear. And, once CD burners came down in price, well
you could just burn JPEGs onto a CD (which, you might recall, many DVD players can show
as a slideshow on your TV). You look back at Kodak’s history and you
just can’t help but feel sorry for them. And to round out the rainbow, the Blue Book
of 1995 defined the Enhanced CD, which functioned both as an Audio CD and a CD-ROM, with two
sessions on a stamped disc. This was kinda neat, as a CD player would
treat it as a normal audio CD, but you could store photos or interactive material in the
data portion which a computer could access. The Scarlet book of 1999 defined the standards
of the Super Audio CD, a high-res audio format, which is pretty much just a DVD but with audio
only. It also had significantly different audio
encoding, which I won’t go into right now, and multi-channel support. And the last of the rainbow books was the
Purple Book of 2000, which if you thought the Super Audio CD was obscure, well you haven’t
read the Purple Book. All this was was a reduction in pit size and
narrower spacing to double the data capacity of a CD. And, it was only for use as data storage,
not audio. But, when DVDs already existed, what was the
point? That’s pretty much what everyone asked,
and it was practically dead on arrival. But an interesting thing about the purple
book. In a way, it had been implemented (although
much more subtly) long before it was published. See, the original Compact Disc standard was
74 minutes or 650 megabytes of data. But, the vast majority of CD-Rs and CD-RWs
you can buy are 80 minutes, 700 megabytes. It was discovered not long into the life of
the CD that the tolerances were generous enough to space the tracks just a little bit tighter
together without violating the Red Book specs. The purple book just did that to a much more
radical extent, but many years too late. And finally, one thing you should know about
pretty much all writable optical media. The dyes and alloys aren’t terribly stable. Many of the earliest CD-Rs are failing, as
the dye is degrading or the disc is delaminating. If you have any precious data stored on optical
media, you might want to back that up pretty soon. Thanks for watching, I hope you enjoyed the
video! This just about wraps up the saga on the Compact
Disc. I think I hit all the bases, but I certainly
didn’t go into detail on everything. If there’s something more specific you’d
like me to look into, let me know in the comments and I’ll see what I can do! As always, thank you to everyone who supports
this channel on Patreon. I say this every time, but seriously. Thank you. Your support makes this channel possible,
and you are awesome for it. If you would like to join the Patreon crew
to support the channel as well as get perks like early video access, some occasional behind
the scenes stuff, and the inside scoop on the latest projects, please check out my Patreon
page. Thanks for your consideration, and I’ll
see you next time! ♪ exceptionally smooth jazz ♪ So long as the CD reader can tell the difference
between a burned spot and an untouched spot, it will read the data just fine. I need to record that line because I screwed
it up. The development of the CD-R, for Compact Disc
Recordable, meant that no longer… wait… … No that was right. [clears throat] Let’s try again! …was replaced with a silver, indium, antinomy… antiMOny, right? It’s Antimony? Yeah. Antimony Cricket! And it also stored photos in a proprietary
format Kodak developed…. AHH! It technically wasn’t using CD-ROMs, though,
as CD-i discs were in fact their very own category, published… … …in the green
book.