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00:00:00,070 --> 00:00:04,100
If you look at a blank CD-R, odds are you’ll
find these two numbers.

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00:00:04,100 --> 00:00:07,710
80 minutes of audio, and 700 megabytes of
data.

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00:00:07,710 --> 00:00:11,600
You may be surprised to learn that these two
numbers don’t match.

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00:00:11,600 --> 00:00:13,460
See, let’s take the 80 minute figure.

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00:00:13,469 --> 00:00:18,460
We know that the Compact Disc Digital Audio
standard consists of 2 16 bit streams

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00:00:18,460 --> 00:00:20,260
(2 because it’s stereo audio)

7
00:00:20,260 --> 00:00:23,890
each consisting of 44,100 samples per second.

8
00:00:23,890 --> 00:00:28,449
Let’s make it a bit easier and say that
it’s one stream of 8 bit words or bytes,

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00:00:28,449 --> 00:00:31,200
so by doubling 44,100 twice

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00:00:31,200 --> 00:00:34,500
(once for stereo,
once again to turn 16 bits into 8),

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00:00:34,500 --> 00:00:38,630
we find that it’s 176,400 bytes per second.

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00:00:38,630 --> 00:00:41,340
Multiply that figure by 60 for sixty seconds
per minute,

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00:00:41,340 --> 00:00:44,960
and again by 80 for our eighty minute runtime, and you get…

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00:00:44,960 --> 00:00:48,620
846,720,000 bytes.

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00:00:48,620 --> 00:00:54,340
It would seem that an audio CD holds over
146 more megabytes than a data CD.

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00:00:54,340 --> 00:00:55,300
What gives?

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00:00:55,300 --> 00:00:58,620
We interrupt this program for a marginally
important message.

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00:00:58,620 --> 00:01:03,260
In the computing world there is an unfortunate
mixing of the terms megabyte and mebibyte.

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You’ll almost never hear someone say mebibyte,
because it’s a silly word, but the 700 on

20
00:01:08,160 --> 00:01:10,540
this disc is actually referencing mebibytes.

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00:01:10,540 --> 00:01:12,010
What’s the difference?

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00:01:12,010 --> 00:01:15,470
A Megabyte is 1,000,000 bytes, based on powers
of 10.

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A mebibyte is based on powers of 2, so it
is actually 2 to the 20th bytes.

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00:01:20,670 --> 00:01:28,300
So, a kibibyte is 1,024 bytes (rather than
1,000) and a mebibyte is 1,024 kibibytes.

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This annoying debacle has been causing problems
forever, for example hard drive manufacturers

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quote sizes in gigabytes or terabytes, when
your PC works in terms of gibibytes and tebibytes.

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So this 2 terabyte portable drive only appears
as 1.81 terabytes on my PC.

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00:01:43,420 --> 00:01:48,760
But my PC is actually misrepresenting this
figure as terabytes when it is in fact tebibytes.

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00:01:48,760 --> 00:01:53,100
But CDs and DVDs are quoted in mebibytes and
gibibytes, so even though this label shows

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MB instead of the correct M lowercase i B,
my computer does the same mislabeling, and

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since they’re both wrong, they agree.

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00:02:00,950 --> 00:02:05,420
Anyway, all of this is to say, I’ll be using
the word Megabyte, even though sometimes it’s

33
00:02:05,420 --> 00:02:07,360
actually a mebibyte.

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00:02:07,360 --> 00:02:09,380
Please send complaints to:

35
00:02:15,020 --> 00:02:20,860
It would seem that an audio CD holds over
146 more megabytes than a data CD.

36
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What gives?

37
00:02:21,680 --> 00:02:26,720
Well it’s actually more of a “what takes
away” as the CD-ROM standard sacrifices

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those bytes for more precise error correction.

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00:02:30,020 --> 00:02:34,000
As discussed in this channel’s first video
on the compact disc, the CIRC error correction

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used in the Compact Disc Digital Audio standard
can perfectly correct errors up to 3,500 bits long.

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But, it can also mask errors up to 12,000
bits long through interpolation.

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That means that it’s essentially guessing
what the audio samples should be for errors

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between 3,500 bits and 12,000 bits.

44
00:02:53,470 --> 00:02:55,510
Now, for audio samples, that’s fine.

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12,000 bits is less than one one hundredth
of a second of audio, so even though the error

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00:03:00,510 --> 00:03:05,010
correction might be fudging things, you’ll
almost certainly not notice it.

47
00:03:05,010 --> 00:03:07,830
But for data, that’s not gonna do it.

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Data cannot be fudged without serious consequences.

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00:03:11,480 --> 00:03:16,270
In order for the compact disc to store data
files reliably, it would either need to sacrifice

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durability or come up with a new error correction
scheme.

51
00:03:19,900 --> 00:03:21,060
And it did neither.

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But also yes.

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CD-ROMs

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00:03:23,840 --> 00:03:26,100
(or would that be CDs-ROM?)

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use the same CIRC error correction and basic data

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structure of the CD-Audio disc, including
the frame structure, subcode, and all that.

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But more error correction was added within
the frame (which we’ve now formally decided

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to call a sector).

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Of the 2,352 bytes available in a sector on
an audio CD, 304 get sacrificed, mostly for

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error correction, but also for some basic
signalling, such as synchronization and distinguishing

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between mode 1 and mode 2.

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Combined with an additional layer of CIRC
error correction, the CD-ROM standard maintained

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the same durability with zero tolerance error
correction.

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We’ll get to Mode 2 later, but nearly all
CD-Data applications use Mode 1 for its complete

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error correction.

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Now that the compact disc was being used for
more than a simple linear stream of audio,

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a true file system needed to be standardized.

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Initially things were rather ad-hoc, but a
group of 12 computer hardware manufacturers

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met at what was then the High Sierra Hotel
and Casino in Lake Tahoe, CA, where they settled

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on a standard called the High Sierra Format.

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Eventually this would become ISO 9660, the
standard used to this day, however it has

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been extended and improved over the years.

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Now that the CD-ROM was officially a thing,
whole new multimedia experiences could be created.

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With the ability to store images, program
files, sounds and even video, the possibilities

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with CD-ROM were seemingly limitless.

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No longer bound by the 1.44 megabytes of a
3.5 inch floppy, elaborate games with full-on

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soundtracks, thousands of color images, and
more complicated structure could be produced.

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00:05:01,320 --> 00:05:06,700
My greatest nostalgia factor comes from mid-nineties
educational games, like the Magic School Bus

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games or my personal favorite, JumpStart 3rd
grade.

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Seriously, this was a wicked awesome game
and it’s holding up pretty well I’d say.

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[In another day, the world will see the dawning
of Polly Planet.]

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00:05:19,600 --> 00:05:20,600
*buzz sound*

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00:05:21,940 --> 00:05:22,800
[Whoops!]

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00:05:22,800 --> 00:05:24,920
[It seems there’s someone at the door.]

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00:05:24,920 --> 00:05:26,240
[Let’s take a little peek!]

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Anyway, of course home computers weren’t
the only beneficiaries of this sort of vast

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data store.

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Video game consoles soon appeared which could
take advantage of it, in fact one of the earliest

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was the Philips CD-i system.

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It technically wasn’t using CD-ROMs, though,
as CD-i discs were in fact their very own

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category, published in the Green Book.

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But unless you’re either very young or were
living under a rock through the 1990’s and

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early 2000’s, I’m sure you already knew
what CD-ROMs could do.

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But the OM, in that CD-ROM, man that’s a
bummer.

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Sure, having 700 megabytes at your disposal
is fantastic, but no one has a CD manufacturing

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00:06:03,090 --> 00:06:05,500
and duplication facility just at home.

97
00:06:05,500 --> 00:06:07,050
But wait, they do!

98
00:06:07,050 --> 00:06:11,670
The development of the CD-R, for Compact Disc
Recordable, meant that no longer would you

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be forced to write up a contract with a commercial
CD pressing facility for at least 10,000 discs

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just to make a mixtape, instead all you needed
was a $35,000 machine and a computer!

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It would take until the mid-to-late 90’s
for CD burners to come down in price, and

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even then there were annoyances, but now we're really talking.

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A CD-R, which incidentally is a pirate’s
favorite kind of CD, is constructed much the

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same as a normal CD, but with two important
changes.

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First, the pits and lands molded into the
polycarbonate layer are replaced with a continuous

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spiral pregroove.

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This spiral will guide the laser of a drive
writing to a disc, and it also contains the

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ATIP which tells the drive the properties
of the disc, such as its maximum write speed.

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Right on top of the pregroove is a thin layer
of an organic dye.

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That’s why CD-Rs are sometimes a strange
color, or even just a little bit off from

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the normal silver.

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Then on top of the dye, a partially transparent
thin layer of metal, usually aluminum, is placed.

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This allows the laser light to be reflected
back while still being influenced by the dye.

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To burn data on the disc, the laser switches
from it’s everyday gentle glow

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to an all-out LIGHT CANNON

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of FIRE LASER,

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and the high intensity
heats up the dye so much that its optical

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properties change.

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That’s right, CD burners are literally burning
the equivalent of pits onto the disc.

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Once it’s been written, almost any CD drive,
going back to the earliest CD players, can

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read these discs.

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The parts of the dye that were made into a
“pit” by the writing laser will dim the

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reading laser’s reflection, which is much
the same as how real pits cause destructive

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interference.

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So long as the CD reader can tell the difference
between a burned spot and an untouched spot,

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it will read the data just fine.

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Being able to store data files onto a compact
disc at home meant that just one of these

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guys could replace hundreds of floppy disks.

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But now we had a new problem.

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Remember how in a normal CD, there are three
parts?

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The Lead-in, program area, and lead-out?

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Well, if we stuck to this limitation for the
CD-R, then if you were to write as little

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as a Word document on a blank CD,

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you’ll
have written the lead-out,

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and now the disc is done.

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00:08:19,620 --> 00:08:23,120
The Orange Book introduced the standard of
multi-session writing.

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Now, after the lead-out of the disc, another
lead-in can be made.

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Each time a new session is made, the lead-in
is updated to include the location of all

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the files.

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00:08:32,800 --> 00:08:36,730
On a multi-session disc, the drive will look
for all of the lead-ins, and once it finds

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the last one, it basically just ignores the
rest.

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This is also how a file can be “deleted”
from a CD-R, as the latest lead-in may simply

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not include it in the table of contents.

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But the data is still physically there, and
there are ways of getting to it.

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Of course, the central limitation to the CD-R
is that is a write-once, read many format.

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00:08:58,010 --> 00:09:02,420
In fact, its original name was going to be
CD-Write Once, which I really wish had been

147
00:09:02,420 --> 00:09:05,560
stuck with because we could have called them
CD-WOs!

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00:09:05,600 --> 00:09:07,040
Woah!

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00:09:07,040 --> 00:09:09,560
But, we wouldn’t be stuck with write-only
for long.

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00:09:09,570 --> 00:09:13,930
Interestingly, the Orange Book detailed a
rewritable CD based on magneto-optical technology

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00:09:13,930 --> 00:09:17,580
in 1990 (the technology behind the MiniDisc).

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This never made it to commercial production,
but the CD-MO would have been the perfect

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companion to the CD-WO.

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00:09:24,030 --> 00:09:28,029
Instead, we got the CD-RW in 1997.

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This is functionally identical to a CD-R,
but the organic dye layer is replaced with

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a Silver-Indium-Antimony-Tellurium alloy,
also called by at least one person

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00:09:37,840 --> 00:09:39,370
AgInSbTe.

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This alloy has a unique property which alters
its reflectivity based on phase changes.

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In an unburned disc, the alloy is in a polycrystalline
structure.

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00:09:48,260 --> 00:09:52,871
But when the laser heats it to somewhere in
the neighborhood of 500-700 degrees C, it

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melts it.

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00:09:54,050 --> 00:09:58,580
And when it solidifies, it no longer has the
same crystalline structure, and thus it reflects

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light about 15-25% less intensely than the crystalline
parts.

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00:10:03,430 --> 00:10:09,270
So, spots that are melted by the laser turn
into sorta pits, and spots that aren’t remain

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sorta lands.

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00:10:10,320 --> 00:10:15,470
What allows the disc to be re-written is that
when the alloy is heated to around 200 degrees C,

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it doesn’t melt, but any parts that have
lost their polycrystalline structure will

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actually reform.

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This effectively erases all of the burned
pits, and allows the disc to be written again.

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CD-RWs have several severe limitations, though.

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Unlike a CD-R, these discs generally cannot
be read in standard drives.

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Because the change in reflectivity between
a pit and land is so slight, a CD reader needs

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to be much more sensitive to pick up the data.

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After the introduction of the CD-RW, many
standard CD readers were made more sensitive

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to accommodate them, sometimes branded as
Multi-Read, but it certainly wasn’t universal.

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Another big problem of the CD-RW was that
the discs weren’t always backwards compatible.

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Because of that phase-changing alloy, there
is actually a minimum speed to write the disc.

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This basic 1-4X disc will work in pretty much
any drive, so long as you can force it to

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burn slowly, but later, higher-speed discs
might need a minimum speed of 8x or more,

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00:11:15,980 --> 00:11:19,800
so if you only had a 4x drive, you’re SOL.

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00:11:19,800 --> 00:11:22,770
And before we put the CD to rest, let’s
look at some of the other stuff that those

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00:11:22,770 --> 00:11:26,390
crafty engineers at Sony and Philips jammed
into here.

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00:11:26,390 --> 00:11:28,910
Remember the subcode channels R through W?

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00:11:28,910 --> 00:11:30,800
Eventually these would get used.

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00:11:30,800 --> 00:11:34,740
CD+G, for CD Graphics, was used in karaoke
machines.

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00:11:34,740 --> 00:11:38,470
The first CD+G discs were released in 1985.

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00:11:38,470 --> 00:11:43,760
This was further refined into the CD+EG, standing
for Extended Graphics.

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00:11:43,760 --> 00:11:49,440
In what seems backwards, it would take 11
years for Sony to introduce the CD Text format,

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00:11:49,440 --> 00:11:51,200
in 1996.

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00:11:51,200 --> 00:11:55,320
Also using the R through W subcode channels,
this was essentially a way to add metadata

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00:11:55,320 --> 00:11:58,570
such as track titles, artists, album, and
all that jazz.

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00:11:58,570 --> 00:12:03,780
Oddly, I can’t find references to it being
used for lyrics, which seems a wasted opportunity

193
00:12:03,780 --> 00:12:05,760
as there definitely is room.

194
00:12:05,760 --> 00:12:08,410
Remember the Mode 2 in CD-ROM I talked about
earlier?

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00:12:08,410 --> 00:12:11,140
That’s right, I’m putting it in the same
video this time.

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00:12:11,140 --> 00:12:16,720
CD-ROM Mode 2 sacrificed some of the error
correction of mode 1 for a larger data capacity,

197
00:12:16,730 --> 00:12:18,650
about 800 megabytes.

198
00:12:18,650 --> 00:12:22,310
You wouldn’t want a computer program or
documents stored in Mode 2, but for things

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00:12:22,310 --> 00:12:26,450
like video files or large collections of images
where a small error will simply result in

200
00:12:26,450 --> 00:12:29,980
a glitch or artifact, it was OK to use.

201
00:12:29,980 --> 00:12:35,280
Video CDs, defined in the White book, used
Mode 2, and now that I know that, VCDs make

202
00:12:35,280 --> 00:12:36,920
a lot more sense to me.

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00:12:36,920 --> 00:12:40,930
The video compression of VCD is ridiculous,
but knowing that it’s actually playing with

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00:12:40,930 --> 00:12:44,670
800 megabytes makes it seem a little less
crazy.

205
00:12:44,670 --> 00:12:46,300
And there were other odds and ends.

206
00:12:46,300 --> 00:12:47,140
The delightful

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00:12:47,140 --> 00:12:47,960
beige

208
00:12:47,965 --> 00:12:51,790
book defined a standard
for photo CDs in 1992.

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00:12:51,790 --> 00:12:56,890
The standard was a little ahead of its time
though, as in 1992 CD-ROM drives really weren’t

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00:12:56,890 --> 00:13:01,300
that common yet, and it also stored photos
in a proprietary format.

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00:13:01,300 --> 00:13:05,660
Kodak developed the Photo CD in a time when
digital cameras weren’t really a thing at

212
00:13:05,660 --> 00:13:09,960
all for consumers, so in a sense it was a
very clever product.

213
00:13:09,960 --> 00:13:14,780
Get your film developed and receive a disc
with very high-resolution scans for future use.

214
00:13:14,780 --> 00:13:19,920
But by the time CD-ROM drives became widespread,
digital cameras were starting to appear.

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00:13:19,930 --> 00:13:25,790
And, once CD burners came down in price, well
you could just burn JPEGs onto a CD (which,

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00:13:25,790 --> 00:13:30,740
you might recall, many DVD players can show
as a slideshow on your TV).

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You look back at Kodak’s history and you
just can’t help but feel sorry for them.

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And to round out the rainbow, the Blue Book
of 1995 defined the Enhanced CD, which functioned

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both as an Audio CD and a CD-ROM, with two
sessions on a stamped disc.

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This was kinda neat, as a CD player would
treat it as a normal audio CD, but you could

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store photos or interactive material in the
data portion which a computer could access.

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The Scarlet book of 1999 defined the standards
of the Super Audio CD, a high-res audio format,

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which is pretty much just a DVD but with audio
only.

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It also had significantly different audio
encoding, which I won’t go into right now,

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and multi-channel support.

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And the last of the rainbow books was the
Purple Book of 2000, which if you thought

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the Super Audio CD was obscure, well you haven’t
read the Purple Book.

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All this was was a reduction in pit size and
narrower spacing to double the data capacity

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of a CD.

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And, it was only for use as data storage,
not audio.

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But, when DVDs already existed, what was the
point?

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That’s pretty much what everyone asked,
and it was practically dead on arrival.

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But an interesting thing about the purple
book.

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In a way, it had been implemented (although
much more subtly) long before it was published.

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See, the original Compact Disc standard was
74 minutes or 650 megabytes of data.

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But, the vast majority of CD-Rs and CD-RWs
you can buy are 80 minutes, 700 megabytes.

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It was discovered not long into the life of
the CD that the tolerances were generous enough

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to space the tracks just a little bit tighter
together without violating the Red Book specs.

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The purple book just did that to a much more
radical extent, but many years too late.

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And finally, one thing you should know about
pretty much all writable optical media.

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The dyes and alloys aren’t terribly stable.

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Many of the earliest CD-Rs are failing, as
the dye is degrading or the disc is delaminating.

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If you have any precious data stored on optical
media, you might want to back that up pretty soon.

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Thanks for watching, I hope you enjoyed the
video!

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00:15:34,589 --> 00:15:37,210
This just about wraps up the saga on the Compact
Disc.

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I think I hit all the bases, but I certainly
didn’t go into detail on everything.

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If there’s something more specific you’d
like me to look into, let me know in the comments

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00:15:44,630 --> 00:15:45,700
and I’ll see what I can do!

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00:15:45,700 --> 00:15:49,010
As always, thank you to everyone who supports
this channel on Patreon.

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00:15:49,010 --> 00:15:52,010
I say this every time, but seriously.

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00:15:52,010 --> 00:15:53,010
Thank you.

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00:15:53,010 --> 00:15:56,430
Your support makes this channel possible,
and you are awesome for it.

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00:15:56,430 --> 00:16:00,200
If you would like to join the Patreon crew
to support the channel as well as get perks

254
00:16:00,200 --> 00:16:04,709
like early video access, some occasional behind
the scenes stuff, and the inside scoop on

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00:16:04,709 --> 00:16:07,720
the latest projects, please check out my Patreon
page.

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Thanks for your consideration, and I’ll
see you next time!

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♪ exceptionally smooth jazz ♪

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So long as the CD reader can tell the difference
between a burned spot and an untouched spot,

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it will read the data just fine.

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I need to record that line because I screwed
it up.

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The development of the CD-R, for Compact Disc
Recordable, meant that no longer… wait…

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…

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No that was right.

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00:16:33,460 --> 00:16:35,380
[clears throat] Let’s try again!

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00:16:35,380 --> 00:16:38,200
...was replaced with a silver, indium, antinomy…

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antiMOny, right?

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00:16:40,880 --> 00:16:42,020
It’s Antimony?

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00:16:42,020 --> 00:16:43,020
Yeah.

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00:16:43,700 --> 00:16:44,800
Antimony Cricket!

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And it also stored photos in a proprietary
format Kodak developed….

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AHH!

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It technically wasn’t using CD-ROMs, though,
as CD-i discs were in fact their very own

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category, published…

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00:16:56,700 --> 00:17:00,140
…

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...in the green
book.