You are puttering along back in 1992 with your 486SX/25, your 120 meg hard drive almost full to the brim, and you decide to plunk down $300 or more for a CD-ROM drive. You finally manage to get it installed, and pop in The 7th Guest, which tended to be packaged with the drives at that time. Holy CRAP! 650 megs on one shiny little disc!

CD-ROMs were actually special back then. Durable and massive in capacity. Whoever thought back then that today we'd be getting CD-ROMs as junk mail. Ahhh, nostalgia...
I once had a 1x CDROM. I used it to clean mailing lists by comparing them to the Post Office's CD of every address in the US. It's the sort of process I'd start at night, and it would finish in the morning.

I loaned the drive to my brother once I got a different job, and he broke it. I miss it now - I think it might be a collector's item! I wonder how much I could get for something like that on one of the auction sites?

Anyway, I felt like such an alpha geek, having one of the first CDROMS. Those were the days!
Like most computer backing store, a CD-ROM is just a huge load of 0s and 1s. The data is read with a laser in a CD-ROM drive. Here is a diagram.


\ \
 \ \   <- laser
  \ \



///\/////\\\\\////\\\\\/////\\\////\\\////\\\///
------------------------------------------------ CD-ROM

The laser iterates over the surface of the CD-ROM, shining on those dashes. They represent little reflective bits on the surface of the CD. The CD-ROM drive has sensors to catch this reflected light. If a certain sensor is activated, it's a 1. Otherwise, it's a 0. Nice and simple - the dashes are just reflecting the laser in the appropriate direction.

The reason CD-ROMs are read-only is because the process of "burning" these reflective surfaces could only take place once on a CD. Now, there are a hundred or so layers of the reflective material on CD-RWs, so one layer can be burnt totally away and a series of data burnt into the next layer. Cool.

CD-ROM stands for "Compact Disc Read Only Memory" and is a method for storing data on the audio-intended compact discs brought to us by Sony and Philips. There are a number of different types of CD-ROM, including stamped aluminum/plastic CD-ROMs, CD-Recordables or CDRs, CD-Rewritables or CDRW/CD-RWs, amd extended-play (from 70 up to about 90 minutes long) and three inch CDs of all of the above types. A drive which reads CD-ROM discs is also called simply a "CD-ROM".


J@XSKSKKggggKKKXXSKXXSSXSSSXZXZ2XXSSZZZXXSS22X2JZ222KS2X2ZXZZZZ22Z222ZZZXXZ3i1iJZXXSSZJ2JJJJJJ22Z  3Z177112JJJ333JJ21371Z  2J1:71iXXJ3J3JJ71J3311111333111111113113ii1ii  i37:;7721ii111i11iJ1iiiiiii1i1
iBXSKXXXXXSSSXKKKKSSKKSXXZ22XKKKXZXSXSSKKXXXXKXZSZZZ:     1Ji1XXZX22ZXZJS2Z@@@@HEEgXSSSSSSSXZZKZS. 22Xi;JZgX2ZXXZ2ZX2XJZS  222iJ3;KKZ2XJ2SZZKSSSSX22ZXXX22ZXKSSKSXX2J3Z2  JX27;;7gK2ZSZ2ZKX1XJJZXSXXZJ33
3EKg@KKXSSKSXZXSSXSSZgKSgSZKgSSSX222ZZZZXXXKZSXZSJX2    ;;1SKSSZ2SSSSXXXSZ2ZXXXSKKZZXXXKXZZ222ZJZ. XXZ31J3g@KX2ZXXZ2ZS2ZX  SSJ.;11KSJJXXXSXJJZ3JXXZ2ZXX2JZZJ132J3iiJZJXJ  3KZ117igSJ11313JJi3J2J31713331
JHZSSSSKSSKSSXKSSKgKZZ2ZKS22XZZXSKSXXSSSSXJSXZ22X1Ji 1@S23;3gZ3XXZXSXZZXZXSXXX222J2XSX22XSKXZZX1S; JXZii22SZJZZ2J3JZZ37JX  32J.,i1@K2JZZZZ21122SX22ZZ2J2Z22XKXJ22JJ2J73J  3J7.:i7gSJ13Z2ZZJ311JJ11XZX22J
1BSgXXX@KSXSSXKXSgKXXSSSSSSXXXZZXX22ZZXSXXXSX22XX2X7 ZX1iKXZHKZKX2XXSXZ3X2XSX2ZSX2ZSX2XSZJJZZXKJg1 :WSiJZXKgXXZXSSXXJ1i32  JJJ771:KS2J23JZXXX2J313J3113J2JJ31JZJ3J222JJZ  3JJ7127gKZ3XX2ZJ1222311i;137i3
1BSBKSSSSSSSSXKXXXXSSSSSXXXXXZZ22ZXSSSSKKSSXSXXSS2Z. gXJiJ31SXJZXXKSXXZ3XZZZZZJXXZZZZ23ZgXJSXJ22SS  33:132SXJ3JJZZ2X2JZJX, XSJ113i@K2322ZSXJ332SZ2Z2ZZZ22ZSSX22KSX21133X  ZXZ1i1,XZJ1333J31132317.     3
3BXKXSKZSSSSSKKKXZSggKSSXXXXXSKSZ222XZXXXSSSgKZZXJZ  @gS7JXKEBJ2SSgX2SKZXX22XXJ2Z22ZXSXZ2JJSSXKSSgJ  2JSKgHKXXSKKX2XSXZ2Z. 3X17;73gK2J22ZJJ22J1133JJJ3iiJJ171J32JJ222J3Z  22J:,i;BXJ2ZZSX22i22J7       7
1KZKSSXSKKSXXZXKKKKSZXZXZZZ2ZZK@@BXXXSSZXSJSX22ZXSK: KKX7i22gHKXXZSSXXZJK2JJSBKK@SXXZZZJZSSX2JXXXXggBKS@gKS2SXJJZZZX2J2ZJ  iZJi7i1SXJ3J3J2JJ2XXZZJZZK@KXJ2SX21JZ2J22JJ2Z  231:7J7BgS211313J133i   ;171.7
iBKZXKXXXSKKSSSSKKKSSSZSXXX2SZJi;11X2222XXXSKSXSSXK; 2XKXJXZSSZXgKZJXKXJ2JXX1i::11123JXSXZXXZ2X22ZSSXgggKSXZZZZZZZXX2J3JX, iSX77J:@K22XXXKX3JJJ1J1J7   1X23i32K333JJ3111  XZ2771:SJ3112XSXJ32X2. :gS1iiJ
1HKXggJKKKSKSSSSXXZXXXSSXXX21    ,.1K22XZJKJX2JJ22X, SKS7;ZZggXXKKSXXSSSJJXJ     ,1Z3iJJ3J2XXXXXSSSX2ZZZZXSKZXX213XJ1217J  7gZ,.1 gK232J2X2JJJJJJ      .7iJZS2iXZJJJJJ22  ZXZ7:11HZ3JSZ2JJJ232J, 7J1;;13
1gXXSKZSXXSSSSXSXXXZZZKSZXXJ:   ,:,2K2ZXXZX2KKSXSKX, XXKJJX2KgS22SSXZ2J1JXZ   :,, :XXZZJJ2ZX2J2SS23JZXZ22222SKXSSZ222ZXZ2  1XJ7,2;SS23JJZ3JJZZ2JZ   .   12211J733JJ2JJZK  XXJi3J;@S37J3JJJ331Ji  31J1:i1
1@SKXSKSSXZSKS@KKgKSSSX2K2ZJ  3@gJ31ZSSXXXXKSXXZZZS; X@Si3XZKKZSSKSXKKSZSZJ  2Z2SJJgKJZXSZZKXXXXSXJ2S2222222J2ZXSXZZ23JJJ  3Z1,:J3KKXJJ2XXXS21J17  SJ1i;7ZSJ322XJZSX23JJ  JXJ:;i;2ZZZXZJ33J32JJ. 32J3 ,i
3BXKXZXSKSZXSZKZZSSXXSXJKJZ2 :KS23X3X@SXXZSKXXSKX2S7 7S273ZZ@SXgKXZZXSX2SXX i@X1X21SgKSXS2JgZXXJJZZ22ZZZ2ZZZ3J22JJ22JJJ32  1SZiiiigXZJ2Z2Z222JJZ7  KZ2223XSJ113ZJ2ZJJ2S2  3SX71J3gX32SX2JZZ2XZX: i22i 3J
1@2SZXKKSSSSXXgXXSSXXXXS@2Z7  KZJ1ZJZ@KSS2ZgXZXSSX@Z  7;7XKKBXXSZKXXXXX2J22 ,KS7J1iK@KZJX2JgZXXZ2ZSXJ2XZJZXZZXXX222ZZX22K, 2KZ1;i1@XZJZX2J23JZ3Si  KX371JSKXXXXJ2222ZZJZ  ,KZ ;i7@S33JZ2J23733X; 7XX3,J2
3@XKZSgKSKgX2ZS2ZSSXSZZXK2S2  gSX:1XS@SZZZSSSSXXSSHK2SXXK@@BBXXK2SSSXXSKSZ2  JK;111g@XZ2XJJSJJ2XXZSSJ3Z212XJ2ZZZJJ22ZXJ3X. JX2i.7iKKSZ2XZJS2iJ2Z,  2Zi.73ZXZZ232ZZXSS1XK3  ,::3SXgK23SX23JJ3XJX; :2Ji .i
1SJZSXX3i3JZgXKSSSKKKZKSi2Z3  XgXiJZXSXZXSSZXXXXXXSXS@@gKSg@gSSSXgKSgSJSXKg: ,1iJXXSX2XKSXXXZZSXJ13J1SX22XXXZZJJZSZZ2233X  1Jii;3iXXJJ123ZZX3i1X1 ;@J2;J2ZKZi1XK2JZ222gZXXi;1KHBggXJXXJZ32K12JJ, :JJi.JJ
igXJ2,     iZ7SXZXSXXSKZ3SZJ  ZXJ71ZZg@XXXSKSSKggSSSKKKKg@B@SZZXXSZ2SXXKSK@Z;,:J2XK@KZJZ2ZXSXXXSXJJ2ZXZJ33J2ZZJ3JZ3J22JJX  iBS1721SKZ2JXJ2JSSZSX1 .gXX ;JX@K2J2Z2XSX2JX2XgKKgg@gSS2JX2JZ33273J2, ;gZ7 i1
3K2S@  .77;JXJgX22XXZSXZXKSZ  KKKZ3ZZg@SXSXKXZZSSXSKKX22ZXZZSKSXSgZZXZZ2Z2ZSKXSgSXK@KXS@gKX2JJ3JZZZZSSK@gKXJ2XXZZX2J3JJ2K, :Xi:;3;S@XZZKZZJX2JZZ1  17;;22XX2J2ZXX2ZXX2X2J2XXSXKS2X2JZJJZZXSZ222:  ZZ,7#g
1g2KS iSgKZ33gBX2ZKKXJZKXXKX .gZ21;JXXXZXKSKKSXXXSXZZSKgSSXJ2XXXSS3XKKKZSgZZ@@KH@K@gXXZ2XX2J2SKi733.     1J11JXZXXZXKSJJX, ;@@2:i32gZJ2K22JZJ1ZS2   JJ32XKS22ZJZX2JZZ3JZSSSXZ1JJJX22SXX2JJJ2ZJZi ;KSi ;:
7K1K; J@XJJ22KSKXXK2ZSKXK2K3 .X2X333ZggXZKX@XJJXSXKXSK2ZZXSSggX2ZXSSX2ZXZXXXZZXS2XJ7JXSXJ2SZJJ2iXX      ,113JJ2J33i3J332K  72J7.3JSgXJZK3JZSXZXKWE3,iJgKH@KX2ZX2JZX2ZKXXZ22JJSKX22Z2JJJJ2Z2JX231  1@  7J
3BXB; KBX3JXZZKgKg@KSSSZX1SK:;221;X2Z@gZZSXgSSKKKXXZXXZXXSS2KK3JXKSX2J2S2Z22J2ZSJZSSKS2XSXZSXXS2SJ   J3J13SSX2JZKKSSXZJ2g; JSZ1;JiXKSJJX222222212KXXX2gKgKXXXZ22Z22XXJJZXZJ33J33ZX2222ZX2311JZ22   . 3ZX
1@XS, ZZJ1JXS@BSZ22SSXZ2K32J ,X@K1ZJ1gBSXSSKSSSSSXSgKXSX2XZJXSZXKg2JZSZJ12XX2J3XZKKJJ22XSXZZZ2ZJ2: 7H21Ji7SSX112Z3JJJ2JJKi :KS7 31SSXJJXX222XSS2XK2S@KK2SXXZZ22XSXZSSX222JJJJ2Z23122XXX2JJ2Z32XK2.7J3KZK
iHXZ; 3XSZJ1JK@2XSZKSSXJgXS2 .22X71ZZBgJ3ZXKSXZZ2Z2Z2JSXXSKSX2SX22XXZ2ZZXXXZZZXK2111ZZ221JX2JJJJZ; ;gXi2Z1SSS2ZgXJ2ZZSXJZ;  JZ3JgJHKXJJZ2XSXZ2ZX2Z3JJ32J2ZXXJZX2J22JJK23J2ZZJJ22Z2J22J3JJZZ2Z3JXK2XSX@XK
i@2K1 JSXJ232@WXXSXSJ2K2KXXZ:;KKSZ2JJgSZSSgXXSSKSXXXZJJ2ZXXZXXX22KZJ2XXXgJ32XZZ2XKXZX2XSJ2XXXXZJX: 7KXJ7J2SXK3iJJSSX2ZZ2SX, ;i712JBX2XSX2XXZ332XZJJZZ2ZXZJ2ZJ3JJZXJ33JZJZJi3J2XX2332ZZZ2JXZJZ1i1ZSXKSgX1
3gX@7 J@KZiX22@X2ZXKXKgZKSSS, XX3133XBgXXZK2ZZXSXXJ2KgKKSKKXZZ2ZZSXZZ2J1SJ12XXKZXZ3J31XXZSX31JZJX1 :K21,73SKKZ2SSXX22ZZXgBBXJ2KKK@@XZXSX2KZ2XXJJ2ZZZ23111132JJZXSZ32Z13J2Z2J3JJJ2ZZJ3J2222J1ZZ2J31i1;32i
1@X@. 3SX1;JZ2B@SSKXXXSZS22X7 ZEZ;X2ZgKSX2gSSXXX2J222JJ373X2J33J2XZ2JJ2ZZXSX:    ,3gXZSZJZZ2XS21J1 ,EZJ73JXXSK2XK22ZSKZXX2XgKK@B@XXKKZJJ2X222ZZZXXZ3322ZSZXXZ2Z1J2Z2J22Z31J31JJJJ2J11332233222J2JJ3S71J1
1K3K3 XSZ13JXKKKSSKZZXKSSJJXJ  1::gXX@gSXZXSXZZZ23XS7    .13XXXX2XXXXZ22i31       1S172X2XgX22XXSJ  EK3;i3SKSX22ZJ2ZXXJZX2ZZ2XX2JZZ33ZXXZXSSZJ313Z2J11i1212X2JZK3122J33Z2XgXZZJJJ32XZ2JJJ132i3J1i13ZiJS2
iBSH2 3KSXZ2JZgXSSX2ZSSZXKSZ2,.Z3JBS@gSXK@KKSXSKSZKX     .;iZJJZJSX22XZ32X1   ;J: iX2i133JZ2ZSZZSZ  :,.iJXBKZJSS2XKZ2XSSSXXSSXZZXSKKKX2J2S23JJJX2J2ZZZZZZ13371X1JZJJZJ133i7i3X22XJJ31XZZXZJ3Z233117J3i3i
1@2S, 2@SZJJJXHX2XKSSggSZZS@E@ZKSK@K@SKKX2SJZXXX2JSJ  Z2JJ11X2JZ2XZJJZZ1JXX ,JXKZ112XX2JZXSZ22XZXK1  .3gSSgJXZSSZSS2JZXXZ22Z2J3J2Z322JZZ1ZJ2XZ3JZJ33J311132Z31J1XXJ3J2J1JZXKZZZ2ZXZJ3113JZZ2J11332gJJ221
igXB; ZBK211J@HZ2S@ggSXKgKS2ZKKKggKgSXKgKSKXXZXX23Xi 3#KJJJJgSJ22J2ZSKS3JS1 ,KE2113S@KXX233ZZ2SX2XgSSSSBgK@XSZXSXKXZSXXXXXXXZZJJ2ZSZ2ZXXJXJJJJ3ZSZJXZ33ZZi7JXZJZX332JJZi23.   ;;,;73XZJ1i11337737,.:,123
1K2K2 2SX21ZX@BSXXSXJZXS22XSXXXXS2ZKKSXXZXKgX2ZSSX27 2HZ71JZ@KJJXKSZJ2222K1  3X7733KKJiJSKSX23ZXZXKX2E@BBgSZKXSX2Z22S23J2ZXXXZZZ22SXXX2JXKXZ2JJ313i;7,7ZJ3JJ2J1Z2J32Jii22.     ;1Z11233J22JJX7i1       7
i@X22 XEgZ1ZJXgKXZSKZZSKX2ZZZXX@SZXXKXXSXZXSZ2ZZ23@2 JK2112ZKKJJ2XXXXZZXJ3J.JK23;33S@KX32XXSSXXX2ZKS3Z2ZXZZ22222ZZZSKZ2ZXZJ2JJ22J11J22JJX122JJ31J1     .ii11i77X2Z3123J3        ;SJ71JJJ2ZZ2373i       ;
3@ZX2 3@2J3XJggS22SKXXXX2XKSZ2J23ZKXSZXgKXXgSXZZ2JSi JSJ73Z2SgX22XZ2XXXZ3Ji  JSK:i3ZXXZZXX2J2XXXXSSSZKZJJ2J32SXXKXZSXJJJSSZXZ222ZXKXZXSX23XXJJ337       ;i23i323iJJZX13Z:  1ZXZi7SS13ZJ3333J113:  ;1,7i1
3@X@Z 1KX2iX2SKSZXKgXXSS2XKKKX2SXZX2X2ZXXXKSXX222XK1 2@XJ33JSgXZZZ222ZXK2@@  1X1 3JJKSZZZZXXXZZJ2Z22SSXXXZXSX222ZZZ22222JJZXXZ2222Z222Z2JXX2J2ZX:  ;132i;3XXJJZ2JZJ2Z1Z3  JHK1317XS23113J2221JJ, :gE;:1i
1@Xg@ XSSZ722KBKSSKK2ZSS22ZX213XXZ2ZKgSZZ232J2XZJ3X7 iZi77J2XKJXSgggSZZXZX3   :iiZ2X@X2ZZKgXXXSXXXZ22Z2JJJ2ZZZXZZZJ2SKX222J22Z2JJXZZSXJ3X22JJ2ZZ1 ,@KZ331XgZ1122223ZX3J3  ;gS.:J3XZJJ2J2ZX3i3JJ. .12,.J1
igKS1 7SSZ7ZZKEgXXXXZSKXJJZJ2ggSZKKZZJ2ZZZXKSXXXX2S3 J@S23KSSK322Z22J2ZSSKS1,,1ZSSXK@XXKXXZJ2ZZZZZ22JXZZXXXZXX2JZXXZ2ZKSKgXZZXXZ2S2XXZZXXJJJ3JJ2. .gJ7 732gK3JS2JJ22J2SZ.  Zi.711@@ZZZ111J31311, :JJ: 1J
3@ZS@ ,XZ3;Z2SKXXSgKXXS2J2ZJJZ3. ,3JK2XXJ3ZSKXJ2ZJKK iKX2,22XBXSX2ZSXZJJZJZKXJ132S@@gX2ZZZZZZZXXZZ2222ZXXZ2JXZJ2Z2JXZ2S23J2ZJ331JS3XZJ2XJ2XX222XJ  2JJ.12JKgJ3ZX22ZJ32XZ;  :  JXZgZ1JX2J22J32J3, :J17 i1
1@XSg :g@S122KKXXSSZJ2SKXZZXJ      ,71JJ2XSXJJ22J2SX iX12,33Z@XX2XZZ22XKXSXZXSXSKKKSZ22XX2JXXZXZZ2ZZXJ2ZZZZXSZ2SXJJ22ZXJ223XZXX22SZ22XXZ2JZZJ332i  2XZ,iJJSXJ31X2JJZZJJKK31ZX2SKXX2J2XZ22J31J33, 7ZXJ ;1
1EZZ@  KZ3JZ2KBKXXKgKSXSSXXi   :i7;ZXKgSSS2JJXKgXJZ3 1@J3;Z2XgZ12XSXZXSXKXSXXKXSKK232XXXSZZSZJSSJ2XZZJ2Z2J3JZZ222ZXX2ZK2ZZ3JJ2J13ZXS2ZSZZXSXZXX27 .@X2,;JJXXJJ2gSZJZZJ2ZSX2JXgBBgSX2JZJJJ22ZZ2X7 1XZ, ;3
iHXXg  777JKKS@SXXSSSSXZ33SS: :J2X7i3ZX232ZgKSSKKSSg iESi1ZJS@23SKKXZXSXJ3XZJZ222J32SZ2ZJ32X23S2JZ232ZZXXZZZ2JJJZZJ2JJJJ222ZZSKXZX3XZXXJJZJ3JJ1ZK  317 :11Z211J2J1JSK2XJJXKgKXXSZZZZXXJ3J2JJJ1J. :3Xi:33
1@SK@ZZJ2ZSBHSKSXXXXXXSgS2SX; SKZg31JXgXJ2KJJ2XXXSZZ  KZ.3SZgg22XXZXZ222XJZZ2XZ32X2J22XX2ZSXZZX3J2JJJ22JJJJJZZXXSXZZZ2J2ZZXZJ2Z2ZSXKZZZJXX2ZSXJXX   ;;iJX@B2;1X3XSJ33J3XSJ7i1JJJJJ2ZSX233JJJi12. :1K, :3
1gKK@g@g@@XKWgKSSXXXXSXXJ3XZ: XK2X3J2X@gZJSggKKSXXZ@1 .;;ZXSK2XKJX2ZXZ2SX2SS2Z3JZZZXX1i3JZZ1JZ3J2JZK3JJ2ZXZJ3J2J3322X212J3ZZJZZ23J323ZX22SXJ3JZJK3,;11SSKSZJXSX3XX2222JZZ2ZX22JJZ2J2Z2XSZJJ2i1Z, iXX; i1
iHX2K2Kgg@gKSSKg@@gSXSS@BKSZ; JSSZ;Xg@K22XX32ZZZXKgSX2J3XgBH@KSZJXXXXSZ3Z2ZZ2J3ZS3i2XXXXS2ZgSJZ222Z22KZ1i32Z2ZZJ13XXXSSXX2XKJJZXZiSS2J2XJZZZZZ2JXSXSXJ3S@KX2J3JX22SX2JX31JJJJZSZJZJ3XX1JJ3J3J2X  7Z21 3J
1EKX@ZKKZ2SgK2XXXXXXXKZ331XS7 3Z23,J3KBKSXKZXSXXXXKKSKKSK@B@S2XXZZXXXXXZ23112SXKBS2KKSX2JJJ222JJJZXJ1,1ZX2J3XXZXXZ2J133J2Z2J2J22JJJJ2XXZ12J2XXXJ2ZZK@@KXSXJJSSiX31313JX2JJJ31X3i3JXX33J2JXS13iZ7  ZS, J1
iHSSBJXKggKZZZKSSSSSSKZ2Z2KXi 12SS;JJKgXZXSSXXXXXZXZZKgSXSSX22KKSXZJ332XJXKSZ1.,1J21,7XXSKX23J2Z2i72EXgKZ3332332XXZ22ZZZ2J31222J3ZgZ2ZZZ2gJXXJSXS21J2132ZZ13XZ;X2SKX2XZ222XSZZZXXi1J2XZ213ZiJ2X3  Zi ;J3
7BXS@JJX22XKS2XXXZZZZSZXX32J, JXJi:XZKKXZ23SXZZXZJXZ2XSXXXXXZZSZJSKKXZ2ZZiii     ,3XJJJZXJ1ZZJ333J317 ;JZZ2J2Z22ZZZ22J31J2J1JX22Z2KJJJJ1321XZ73JJ2222J223112X2J33ZX23JJ223J23323JKXJJJJXZ331Z33J    :ZZZ
1BJ2gXZSXSXZZSXSSSXXSK2ZgJZZ; 1XX1iZZXKZ2ZKgXSKX2XKSXZXXXJ2SSZZXZJJZJ2X333Z,      .33773J2JJJZJJ32J      :i3JXJi2J332Z11XX2SXJ322i13JJ2Z2ZXZ11JJZ233JJJJ2J237i2ZJ1322122J313J2XZJ3JJJ23JXX2JK2ZK2, 3XKSX
iBXSSJKKSXSSXZZSKSXZZXXSZ3SZ; 1Xg2:3XKgXJ2KSXXSSZJXZZZXXZXX22ZXSSZJSS222Z3Z;  i2173SgZ13ZSXJJ2JJZZ       1SX1J3323222Z2ZS2122222J3XZXZ2J1J222JJ3Ji1ZX332332Z22ZJJ3JJ23JJ2XXZJ1131JZZJ22J1337ZJZXg@J7XgKK
7@2XS2KXXZZZZXJ2ZZXXXZZX22XX7 JKKJiXXXKSXXXXSX2XSXXZ2ZZX2ZXZZXXZ22JSX2Z3KJi  ,3XX172gKX233XXZ2J1Xi  ,12J7732JX2JZJJZZXZJJJJ332Z22ZZ2JJ22ZZJJ22JJ3i12Z332J111iiJJJJJ22222J3132JJJ11J3JXZ33JZZX2Z232gKKZ3J
1H22gJ7  . :J2XXSSXZXXSZZZ2XZ 1SSZ:i1SBgXXgJSS2JJi1J2ZSKXZJ1J2J3JJ2X22X13ZZ  J2i2SJZKZJ2XSXZXX22X1  WS11J2XZXZJZXJ2X23JXSJ323JJ11213ZZ22J21i33113ZS2331JJ7i22J211133JJ1323113JJ2J32J117122333;iJ3i1113J1
iBZJ@;   , ;KgX2ZSSSKKX222223 ;XKS:KZKgXJJXJZZZSX33S@X2J13XZ2XgKXSSSXZJJ3SS  Sg3JXJ1SS2J2S23Z2J3X3  BZ773i2SS1iJJ223Z2712ZX1iJ3JXZX2X3iJJZJJ11J137.    ,JZ1iJJ32JJJ33iJJZi1J12JJ21JJ2X332J11Z1Z2i1133JJ3
1WSXE1 :3X33;3KX22ZXXS2ZgKKX1 1SX7 2ZSKXJ2S2Z2JZX2133     :323iJZXZZZXXXZSK  JS2::3JXgKJJZJJXSX2X2  gJ1;33XggJ12ZXJJKX1223J32Z32KJX3i3ZX2J2J3JJ71      .;321111JJ2XXZJ33Z1JJi31iii11JZii3J3J22XXJJXZJJJ3
iX1XK  ZSKJZJJgSZZXZ322K@11Z1 1KK1,XZXSSXZZZSSZZX2XJ   ,,  ;2ZJ2XXJJ2XSS22Z. JgSi,JZKgX33X2JJ3J2Xi  gSX7113ZXJXX11J1117221i1i313Z33J32ZJZ1ZJ3ZJ1S   ;i.,:32i3Z3J17i3JJ2i172Z112J32J1JJ13J3JX33J22i11JJ33
1@SXJ,:EgS1ZKJB@SZS@S@KSXJSK1 .K@J1KgKKggK2KSXZZ23XS  1SXJJ2SX23ZX2Xg@XJ3JZ, 7SJ  3JSZ2J2XXXXSSZZ3  @SJ,,1XgX7iXZ22ZXXXXZ2ZXSgZJ23ZJ1ZXJZi3i1J327  JXJ31,7gX.,XKXZJ11iZ2J1ZXZ2J7;333JJJ2J113J371ZJ1J22JJ
J@XXXi Kgg33gXHgXZXgSSSSKgSXS7 ;1732XKXJ2XJ@SXXXZ2X2  1JJ23JSKZiZKZ22J2SK@@7  ,. JgSg2i2KSXSZXJ3JZ  .,.;1J2Sg33XZ2JZ371113i7;;;3Z721JZ232X2223;i1  gg1J231S@Z3XJ3J3i3ii13i.   7J2J1;73i12Z3;113JJJ131i71
1KXS@1 3ZJ;1XJ@SZXKK2SX2XSZSgi.iJZg@gHKJZS2ZZXZZ2ZSX  @@KZJJXB21ZS222ZZ2SJ2Si  12gXZ@KXKX2JJ2JJXSS:  12X22S@X3311XXXX21;1J;     ;37J211J3i13J3113  221 ,JZK27iJX22ZX232;.       7i71J2X2;.3K1J2J11J23JZJ
3EKX@Z :772@@gHKSSSSXZZSKKSXK@g@ZJ@BBgKKKSXXZZXXZ2ZS  @H2:J22@Z3ZZXXXKX3gJJK@21ZXgg@KX333XKXXJ2ZZXZ. ,3Z2XKXX22Z331iJ23iJ;       1JJ3iiJ2JZZJJJJJ  32S,,32gS1iJJ2JJJ1J2i.   .,  1KJ7i313J2Z2i3JJJJ2;i331
iBXS@@@XZZKgK@@SXKS2XKK23ZKKKKKBgKgXKZXKKX2gSSSKXZ2J   :  JSKKZ2SKKXJ2K2KX22ZXgH@gggX2XSJ33J2JZZZJSgXXKgSKKXKZ2Z2ZXZZ2J2K,   73: 7XJ31322JJ3333XZ  3JZ.,7:S@23JZ2J1Ji1ZX    JZJ, ZZ17iJ2ZZJ1171J221ZX3J1
;g2XKZ@HgK@@g@SXXXKKXZXXSXX2ZX223JXZKXXXSSZSSXXSXXKK2,  1KBKSSXSSXJ22XS3J2ZZZZJJ33J2Z22ZXX2J2ZZ2ZJZS12XggXJi22JJ22J22J31Z,   ;JJ1,2SX1322231JJi13  Z33.iZ3KSi3ZSJ2321ii3      1i:SXi71J31322212231;i2123
7HXXKZXSKKKKSSKSSXSgZJXKKSSKS2XKgKZZKZ2J2XXXXXSSSXS@BgSZJZKg@S2JZSXXSSZJ2ZZXXXZXXX22J2Z2ZXKS2JX2ZJ2S1SJ13JJ1XX2J2XXSZ2Ji2:  3JiJ2;JXXi711XZ113137  XZi iJJSX7:1JiJJX2J@Z  gEi72JiSKJ12Z22ZJ71i177J31Z1ii
1MKZXJ2SKSJJZXSSSSXZXSSZXKKXXKKZSS2XXXSKSXZXXXXXX2XSg@@g@@@@KXZXKKZ2SXJ2XZ2JJ2Z22XZZZXXZJJZX2JZJJ3JX71Z21ZgZJ33JJJ33i3X1Si :#@:1SiKSXJZX12XX22ZS2  Z27 13ZSSJ1SXJZJZ1;XX, iXJ;;11KBX1J23iiJ2J33ii2i1J1J1
7SX2@gKggKXSS2SXXSKSSSKJiSKZZXZ2J22ZXXZZXS@ZXXXXXZZSX2KKSKX22SKX2SZZXSZJ@J2Z2Ji11J2J2JJ2ZJ32JJZJ373ZJSX2JZXJXSX2JJZSJ3Z3S;      XZKgX3JXXZXZ2ZZ2i  XB: ;1JKKJ1222JJZJ2J3  7JJ;.11XX;,JKSJJ3;312J3J7K,;11
iKSJXJ3SZ2ZKgXXZ2ZXZ2XgSJJ2JZXSKKSXZZXXXSXXZZ2XSXZ2XXJZ2JZSZ2XSXZZZZZJJ1KJ2Z2Z2Z132JXXJ2Z2JZ2JZ2JJZ21Ji1JXXJZ2J2XZJJJXS1Xg3   1XKJKSX2J17J223JJ2J     iSXZX23JX23i221JJ1  7Xg7 i72KZJi;7i333Ji7;3XiJ1Z11
3BKXK3J22JJXXJKXZ2XXXKXZ2XgSZKXZZZXXZZZXXZ2XXZXXZ2XXKKSgSXSXZ2ZXXXXSXZ2JJJJ2J32Z2J3133J2222JJJJ111J2XKSJ7,:13JZ2J3JJJJJJZXSSiJXSKZ@X2ZXX2XZ2JJ3ZS3   1SXZZZ22ZZZ232Z3JXK:  1:  3JXX71X32SXJ2X221:      i
1gZX@2gS@@KSSXXZXXSXZZ2XX1Z22XJ33JXKSZ2ZSSX2XKSXZXX2XZ3XZ2XXZJJ2XZZXKKXJXZ337    ,1KZJZ22ZXJJ22223;iSJJ2ZXX2Z2JJJJ2Z231JZXKKX@gKgKX11JZ2ZZ1iJZJJZgKXJi32BBKZ2237XJ122ZJX2   .13SXgg3323111i7;:37       7
iKXK2ZZZXXXXXXJXXZZXZSSX2JZXSXXXSKXZS2SKZJXZZJ1JXZKSJ2XXK@X2ZSXSK212Z2S2g2Z7       JX3i13ZZiiJi3i2S:    ,1,;233ZXZJ2J3J2J12X2XXJJZXJZKZ12XXZZZZZZ2SJSMB@g211JJ322J2Z2JSJS2  .XXZXSJ11JXX23JZJ13;   i;:.3
1@SKZSZXZZZXXSXKX22XKXXK@KXJ3J3JXX23X2J2SKXKSKgXJ3ZJZKZJ132XSXJZKKZXX23ii3X7  :J1:,1ZZi1XZZgK21i7i       i332J32J11JJJZ23J21JJi;1Z22J33JJJJ333J2XJZZ2Z13i1JZXZZZJJXZ2Z31JK@BSggKgK2ZX2772S3:31J:   ;J2:3
7K2X2S3KX2J2XK2SSZJJ3JJJ3J2ZXZZZXXZ2XSXZX2,Z113113SXSXXKKXZ2JZSZ323JSS2S22X7  122Z3JXKZ333J2J3ZZXX  , i;.731;  .J21iJ21i3J313JXSJ:JZ3;iJ2ZZZZZZ22777;i7XX2J111iJ2JJ2233231J2ZSXJ31iJZ22ZJ3J21iJ; .@g;iJ3
1@XKKgJXSKgS23JSKKKgKZ2XZX2JJSX2J1JJ11J22Z2XXXK@K13Z2132JJZXJi322XJ1ZXJS71Z,  133Z312SXii12Ji71JJJ   7JZi,3gHgSKKXZXZ23JXXZX2i73XXJZX2JJJ133317,3JX23JiJ1i1JSXJ23131iiJZJ227;1i73J31JJ7iJX21J3SJ  XK  3J
3EXXJg22XXXgg2gZ3JJ2SKSSXKg2JXZSS2JXKXXXXXZ2JJ2J2SKKSJZKKXSSKKZZXK2JXZJ2S2X;  ,SJJ2JZXXZXSKSJXXJJ1   iZJ37222Jiii111J3i237i3311JJ7i7J2JZJX21122;1J17i2XZJ1ii1iii13X32S7:;iiiJ21321J3i3221i13232i  :3  iZ
7gJXJgJJXXZ222SSXXSS13Z23JXXXZ3322222XKKXZZKZ2XZJ1JJJ311ZX2J1JS2i2ZX2J2XZJZi  ;21JZ2ggS2JJ2ZJJ172S     ;33JXXXJ2SXJJ2XJ13JZZZK@S2X22ZJ31;;133J211i,.;i7:;J2JJJJ3J12i332J3JJ37377iiJ2113JJJJJXJ2J     iJ2
7K3XZ@JK2JZXZ2XKKX2ZZXXXJ2Z2JZXXSKX3ii3J2ZZJ322JJK2ZSXJ3J3JZ23JZSKXZZXZ7S2SS   31ZZ2KX2SXZXSX2XZSX  EE7,1;JSXSi;J1iJJ217J23i.    3i77JZ22JJJ1137JXSgKZ23::iii12Z27i7J372X21i;22J21J22Zi73Z212JZS27 :3@gS
JHXg2S1SXX2112K2JZXXZZ22J22i7J2i;i3JgS2J222S22ZXZZ3ZX2ZSXXXXKSZJZXZJ32X2@2J@K11J2SXXgX32J3231;3J2X  JXX;:i2XXK17X2XX22XJZi       37i,;JJJXZJ3JJ117:    7Z22ZZ1;1J2Z2J;11771J321;i13iiJJ17,.7J3112K@3:JgZ
iS32;22@SXXXSS3JXXZZSKXXXX2J3i      12371JJ2SSJ3J231JXZ332311321131JJJ1;7J2XZ32g@@gggX2X23X23JJ72X  ZX2ii332K27JXX2J31313J       ;SX3i17i31123i12       .,,71;iJiZ113J1 .17;:7i77i,;J333XZJKJ332SXJ2BS21
1@2SJXiJ:  :JKSZXKXJZSZ32S2J@Z    :732K31SZ32J113J23JSZXSKSJ111i3KZ2ZXXXSXi1ZXKXXKS2JZXSZJSZ32XiJX  3X; .12gg31J3333XJ13ZX.  :1ZJ,X3JZZ22Z231i;:7    ,  ;32JJJ22iZ13J3212i     .,17:i3113313;i13311;J7ii
1g1ZXg;     ,7Z2JJZXXXKX22Ji2; ;J1J7 1KX333ZXX2ZZ22i2K2Ji72JZXZKX1i2X3131XZ223131i11i33311ZZ32X11X  JKZ7:133K33Z3ZJ7J33JXi  JgS21;XXKJ1233311J223   :X1, ;X3.7SJi21i; 1J;       :ZJ3Ji1371ZJ22J31i;ZZ7J2
i@ZSKK  .;1i71ZgS1i2ZJJXSXKJZ; i22XZJXSKKJigKZJ223213.    ,:3J73J2JZS2J2gS312ZJS2i2XZ2Z23JZZ22ZJJK: iEK1;J2S@22SJZZXX2J12,  KH2  J2KKi7J3XKX177J2  .;7,177SXi:i31XZSXX77   .ii;:iZi,;17;;JZ7333JJ3i;2J1i
ig2J33 .J3ZKX3SSXJ2XXS2JZJZZJ  SX23Z3ZSKX1,32XXSX2ZXZ     .:JXJ3322JJJ2JiJZX31121;i11iJ2JZ1711233Z   ;  :JZ@SZ2ZX21J2ZZJKJ  ;gX, 32gX111ZJ3J2Z171   721177XSgX2X22JJ1112    7;i1i2KXJXSXJJJ13iii1332X23J
7KXKB@  J2XSZ2BKK@gSXX21i13J1  KX37313JXXKgSgS313JJSi  :JJ112ZZ11gX22XX22X11ZXX3JXKSX2SX2XKgXiZX2Sg;  3@gSXXXX2ZXX2J33J3KX;     iZJ21JX2J231111JS   ;77Z3iXX27:7:7J22X32.  ,J11i,3gX;.71171JJ2ZZZJ1.,;i1
1HX3Z2  JJ2231ggS2J2ZSgKKHKZ@1.ZXXiiZSgKZJ1i2XXXZ33Z   71J2JJ2X1;XJ22JJ3Z237JZ22X2i7117,711Z271313SS1213JXHBX23J222ZX232KggZ  iXgiX@XJJ1iXZ333J2J  gE3,Ji7SSJi2SJ22i;27Ji    .;ii2X213231J21;13i;7JXJ111
i@XZSg: 7iJKg2XKZ32SKSXX1JJJK, J27  32SgS33@X222J1JB3 :3:;132gEK32ZJi;;;2XS17JZ11JXKSZJ2X2iJXXSXXZZXS@XXK@S7i3332XJJZZ11JZ2J31i2@XBX3JZ2XKXZZ2JiX  1S  :1iXX3;;Z32J132ZS3  :JSZ1J@X11JJ2ZJ1;SZ233ZZ2J3Ji
i@SSSgi 3J2KgXBEKXSXXSXSJ2XJS: ZSZ23X2X@BSXX3JXXZ2XZ   ;JX2JJ2X232XK@KS2ZJ13i      ,2Z317;7JJ3J3JJ22ZXXS2JK2K@KXXSZ332ZJ13ZKSgKKgSXZJZZ7:JZ2J2212      7J3XSZ3123Z2J2Jii1   72ZJJK2323i1J1JJ3.;i77,:;7JJ
i@XSSgSgS2JXKSgBZJXZZZSSZ223Z7 2XSX,;3SZ17iSXXSSX2JKK,  7XZZXX2JJ2J33J2ZJ333.    ,,73JJ2ZXS21iX222Z2Ji;117J22J3JJ1i1JZX23JJ33ZS2321XJJXJ7;3i7JJJg3  :XKSXZgX32JJ7J2JZSJ2gXi323JJJKZ3JJJ22171Z;7JJ122ZJi1
3SJXXSKgggKSKKKgZ2SXZZXJJ22JJ; 7J3J:7JgKXZ2ZZ2J2Z2XKg1:72KKK@BSZ2JZXXZJ1J321  .32371XZ33J22JJ2ZJJ2Z2JXX2XZ13Z22ZZJ132Z33X2JZJ7i1ii1J32XXZ2S1iZZJZgK113JXXZS37JJ21J23323J2JJX2JSS22J13i777i1XJ17ii,,;::.7

Pits and Lands on a Compact Disc, Greatly Magnified

CD-ROM technology also spawned the DVD, or Digital Versatile Disc, which is gradually superseding it, as well as some proprietary CD formats like the 1GB GD-ROM used by Sega's Dreamcast console game system.

PHYSICAL CHARACTERISTICS

There are 21-minute (80mm/3 inch), 63-minute, 74-minute, and 80-minute CD-Rs (120mm/4.72 inch)which translate into approximate data storage capacities of 184MB, 553MB, 650MB, and 700MB respectively.

Ordinary CD-ROMs are made of an aluminum sheet which is stamped (like a record) and then covered with plastic for durability. In theory, if a CD becomes scratched, the scratch can be buffed out of the plastic.

Recordable discs are made up of at least two plastic layers, a reflective metal layer, and a layer of organic dye, as well as two dielectric layers. Discs without a top plastic layer are highly susceptible to losing parts of the metal layer due to scratching or moisture. The organic layer comes in one of four compositions according to the CD-Recordable FAQ2:

  1. cyanine dye, which is cyan blue in color (hence the name);
  2. phthalocyanine and "advanced" phthalocyanine dye, which have a faint aqua tinge;
  3. metalized azo, which is dark blue;
  4. formazan dye, which is light green.

There are actually at least three other compositions I know of; Silver, Gold, and Red. I do not know what their dyes consist of.

Regardless, a CD-Rewritable is written by burning the organic layer with a laser in order to change some of it from transparency to opacity to emulate the pits and lands (think mesas) of an ordinary stamped CD.

Which color (and hence, which dye) is used in your CD-R makes a significant difference in its behavior because certain CDs are opaque to different frequencies of light, and different CD and CD-ROM players have laser tubes or LEDs which put out different frequencies.

CD-RWs have a pre-laid spiral track which the laser follows during recording. The spiral track makes 22,188 revolutions around the CD, with roughly 600 track revolutions per millimeter as you move outward. If you "unwound" the spiral, it would be about 3.5 miles long. 2

STANDARDS FOR CD-ROM CONTENT

There are a number of formats used with CD-ROMs. Most of them are not competing, but rather provide different feature sets for different needs. Like many standards, they are organized into color-identified books; the "red book", the "yellow book", and so on.

Red Book

This is the format for CDDA, or Compact Disc - Digital Audio. It is the standard format for Audio CDs. It is often combined with other formats on the same disc.

In one second of Red Book format audio there are 75 frames (or sectors) and each holds 2352 bytes of equivalent computer data. Red Book CDs have only one session which can contain no more than 99 digital audio tracks.

Red Book audio is 44.1kHz, 16 bit, and stereo.

Yellow Book

The Yellow book describes data CDs. It is further separated into Mode 1, the original data format, and Mode 2 which can be further divided into 2 forms: Form 1 and Form 2.

Green Book

This is the format for CD-i (Interactive CD), a multimedia computer system (essentially a console game system) from Philips.

Orange Book

The Orange Book describes the physical format for Recordable CDs. Part I describes CD-MO (Magneto-Optical) discs. Part II describes CD-WO (Write-Once), AKA CDR or CD-Recordable. This also includes the "hybrid" specification for Kodak's for Photo CD. Part III details specifications for CD-RW (ReWritable) discs.

White Book

The white book describes the Video CD format, a fixed-bandwidth MPEG1 video disc utilizing MPEG 1 Layer 2 audio (mp2).

Blue Book

The Blue book contains the format for CD Extra, a format which specifies two sessions; A Red Book audio session with no more than 99 audio tracks, followed by a Yellow Book data session. This format is popular for video games and music CDs which have additional material such as lyrics or a music video added to them.

CD-ROM/XA

XA stands for "extended architecture" and is a halfway point between the Yellow Book and the Green Book. Mode 1 CD/XA uses standard Yellow Book sectors. Mode 2 can be form 1 (2048 bytes of data, with error correction, for data) or form 2 (2324 bytes of data, no ECC, for audio/video). Form 2 is used to create SVCDs for example. Its lack of error correction is due to the fact that many video formats (including MPEG) mandate their own error correction, and using Mode 2 Form 2 will allow you to save the space used for ECC.

USES

CD-ROMs are used for nearly everything these days. Compact disc is the format of choice for music. CD-ROMs are the format of choice for software distribution. There are two video formats, Video CD/VCD and Super Video CD/SVCD. Many console video game systems use them; Sega Genesis, 3DO's 3DO, and Philips' CD-i were some of the first. Three inch CDs are cut down until they occupy no more space than a business card and used for utility and demonstration software.

The production of compact discs of all types has become so inexpensive that CDs with various types of content are handed out free in the checkout line of your local supermarket, usually try-and-buy packages for nationwide ISPs. CDs are also slowly replacing printed documentation, especially in technology. Digital documentation has a number of advantages over print media including searchability and a lower shipping weight.

Finally, outdated and damaged CDs frequently find new life in mosaics and mobiles, and other kitsch-art projects such as analog clocks.


References:

  1. Acer Peripherals, CD-ROM FAQ. Acer Peripherals, 2002. (http://www.benq.com.au/products/cdr/service/faq.htm)
  2. Andy McFadden's CD-Recordable FAQ. (http://www.cdrfaq.org/faq.html)

Log in or register to write something here or to contact authors.