CHAPTER 13

What Is a CD-ROM? Chapter 13 703
advertising when these drives first came out. For example, a 12x CLV drive reads data at 1.84MB/sec
no matter where that data is on the disc. On the other hand, a 16x CAV drive reads data at speeds up
to 16x (2.46MB/sec) on the outer part of the disc, but it also reads at a much lower speed of only 6.9x
(1.06MB/sec) when reading the inner part of the disc. On average, this would be only 11.5x, or about
1.76MB/sec. The average is actually overly optimistic because discs are read from the inside (slower
part) out, and an average would relate only to reading completely full discs. The real-world average
could be much less than that.
What this all means is that the 12x CLV drive would be noticeably faster than the 16x drive, and
faster than even a 20x drive! Remember that all advertised speeds on CAV drives are only the maximum
transfer speed the drive can achieve, and it can achieve that only when reading the very end
part of the disc.
Table 13.7 contains data showing CD-ROM drive speeds along with transfer rates and other interesting
data.
Column 7 Column 8 Column 9 Column 10 Column 11 Column 12
Average Maximum Maximum Speed Rotational
Average Transfer Linear Linear Min. if CLV Speed
CD-ROM Speed Rate if CAV Speed Speed Max. if CAV Max. if
if CAV (Bytes/sec) (m/sec) (mph) (rpm) CLV (rpm)
0.7x 107,520 1.3 2.9 214 497
1.5x 222,720 2.6 5.8 428 993
2.9x 437,760 5.2 11.6 856 1,986
4.3x 660,480 7.8 17.4 1,284 2,979
5.7x 875,520 10.4 23.3 1,712 3,973
7.2x 1,098,240 13.0 29.1 2,140 4,966
8.6x 1,320,960 15.6 34.9 2,568 5,959
11.5x 1,758,720 20.8 46.5 3,425 7,945
14.3x 2,196,480 26.0 58.2 4,281 9,931
17.2x 2,634,240 31.2 69.8 5,137 11,918
22.9x 3,517,440 41.6 93.1 6,849 15,890
28.6x 4,392,960 52.0 116.3 8,561 19,863
34.4x 5,276,160 62.4 139.6 10,274 23,835
35.8x 5,498,880 65.0 145.4 10,702 24,828
37.2x 5,713,920 67.6 151.2 11,130 25,821
40.1x 6,151,680 72.8 162.8 11,986 27,808