CHAPTER 13
CHAPTER 13 CHAPTER 13
730 Chapter 13 Optical Storage Note that although no more than 10 0s are allowed in the modulation generated by EFM+, the sync bits added when physical sectors are written can have up to 13 0s, meaning a time period of up to 14T between 1s written on the disc and pits or lands up to 14T intervals or bit cells in length. DVD Drive Speed As with CDs, DVDs rotate counterclockwise (as viewed from the reading laser) and typically are recorded at a constant data ratecalled CLV. This means that the track (and thus the data) is always moving past the read laser at the same speed, which originally was defined as 3.49 meters per second (or 3.84m/sec on dual-layer discs). Because the track is a spiral that is wound more tightly near the center of the disc, the disc must spin at varying rates to maintain the same track linear speed. In other words, to maintain a CLV, the disk must spin more quickly when reading the inner track area and more slowly when reading the outer track area. The speed of rotation in a 1x drive (3.49 meters per second is considered 1x speed) varies from 1,515rpm when reading the start (inner part) of the track down to 570rpm when reading the end (outer part) of the track. Single-speed (1x) DVD-ROM drives provide a data transfer rate of 1.385MB/second, which means the data transfer rate from a DVD-ROM at 1x speed is roughly equivalent to a 9x CD-ROM (1x CD-ROM data transfer rate is 153.6KB/s, or 0.1536MB/s). This does not mean, however, that a 1x DVD drive can read CDs at 9x rates: DVD drives actually spin at a rate that is just under three times faster than a CD-ROM drive of the same speed. So, a 1x DVD drive spins at about the same rotational speed as a Table 13.20 DVD Speeds and Transfer Rates Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Column 7 Time Time Transfer Actual Minimum Advertised to Read to Read Rate DVD Speed Transfer Average DVD-ROM Speed Single Layer Dual Layer (Bytes/sec) Minimum Rate if CAV DVD Speed (Max. if CAV) DVD if CLV DVD if CLV (Max. if CAV) if CAV (Bytes/sec) if CAV 1x 56.5 51.4 1,384,615 0.4x 553,846 0.7x 2x 28.3 25.7 2,769,231 0.8x 1,107,692 1.4x 4x 14.1 12.8 5,538,462 1.7x 2,353,846 2.9x 6x 9.4 8.6 8,307,692 2.5x 3,461,538 4.3x 8x 7.1 6.4 11,076,923 3.3x 4,569,231 5.7x 10x 5.7 5.1 13,846,154 4.1x 5,676,923 7.1x 12x 4.7 4.3 16,615,385 5.0x 6,923,077 8.5x 16x 3.5 3.2 22,153,846 6.6x 9,138,462 11.3 20x 2.8 2.6 27,692,308 8.3x 11,492,308 14.2 24x 2.4 2.1 33,230,769 9.9x 13,707,692 17.0 32x 1.8 1.6 44,307,692 13.2x 18,276,923 22.6 40x 1.4 1.3 55,384,615 16.6x 22,984,615 28.3 48x 1.2 1.1 66,461,538 19.9x 27,553,846 34.0 50x 1.1 1.0 69,230,769 20.7x 28,661,538 35.4
DVD Chapter 13 731 2.7x CD drive. Many DVD drives list two speeds, one for reading DVD discs and another for reading CD discs. For example, a DVD-ROM drive listed as a 16x/40x would indicate the performance when reading DVD/CD discs, respectively. As with CDs, drive manufacturers began increasing the speeds of their drives by making them spin more quickly. A drive that spins twice as fast was called a 2x drive, drive that spins four times faster was 4x, and so on. At higher speeds, it became difficult to build motors that could change speeds (spin up or down) as quickly as needed when data was read from different parts of the disc. Because of this, most faster DVD drives spin the disc at a fixed rotational, rather than linear speed. This istermed constant angular velocity (CAV) because the angular velocity (or rotational speed) is what remains a constant. The faster drives are useful primarily for data, not video. Having a faster drive can reduce or eliminate the pause during layer changes when playing a DVD video disc, but having a faster drive has no effect on video quality. DVD-ROM drives have been available in speeds up to 20x or more, but because virtually all are CAV, they actually achieve the rated transfer speed only when reading the outer part of a disc. Table 13.20 shows the data rates for DVD drives reading DVD discs and how that rate compares to a CD-ROM drive. Column 8 Column 9 Column 10 Column 11 Column 12 Column 13 Single Layer Usual Average Maximum Maximum Rot. Speed Single Layer Transfer Transfer Linear Linear Min. if CLV Rot. Speed Rate When Rate if CAV Speed Speed Max. if CAV Max. if CLV Reading (Bytes/sec) (m/sec) (mph) (rpm) (rpm) CD-ROMs 969,231 3.5 7.8 570 1,515 2.7x 1,938,462 7.0 15.6 1,139 3,030 5.4x 3,946,154 14.0 31.2 2,279 6,059 11x 5,884,615 20.9 46.8 3,418 9,089 16x 7,823,077 27.9 62.5 4,558 12,119 21x 9,761,538 34.9 78.1 5,697 15,149 27x 11,769,231 41.9 93.7 6,836 18,178 32x 15,646,154 55.8 124.9 9,115 24,238 43x 19,592,308 69.8 156.1 11,394 30,297 54x 23,469,231 83.8 187.4 13,673 36,357 64x 31,292,308 111.7 249.8 18,230 48,476 86x 39,184,615 139.6 312.3 22,788 60,595 107x 47,007,692 167.5 374.7 27,345 72,714 129x 48,946,154 174.5 390.3 28,485 75,743 134x
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730 Chapter <strong>13</strong> Optical Storage<br />
Note that although no more than 10 0s are allowed in the modulation generated by EFM+, the sync<br />
bits added when physical sectors are written can have up to <strong>13</strong> 0s, meaning a time period of up to<br />
14T between 1s written on the disc and pits or lands up to 14T intervals or bit cells in length.<br />
DVD Drive Speed<br />
As with CDs, DVDs rotate counterclockwise (as viewed from the reading laser) and typically are<br />
recorded at a constant data ratecalled CLV. This means that the track (and thus the data) is always<br />
moving past the read laser at the same speed, which originally was defined as 3.49 meters per second<br />
(or 3.84m/sec on dual-layer discs). Because the track is a spiral that is wound more tightly near the<br />
center of the disc, the disc must spin at varying rates to maintain the same track linear speed. In<br />
other words, to maintain a CLV, the disk must spin more quickly when reading the inner track area<br />
and more slowly when reading the outer track area. The speed of rotation in a 1x drive (3.49 meters<br />
per second is considered 1x speed) varies from 1,515rpm when reading the start (inner part) of the<br />
track down to 570rpm when reading the end (outer part) of the track.<br />
Single-speed (1x) DVD-ROM drives provide a data transfer rate of 1.385MB/second, which means the<br />
data transfer rate from a DVD-ROM at 1x speed is roughly equivalent to a 9x CD-ROM (1x CD-ROM<br />
data transfer rate is 153.6KB/s, or 0.1536MB/s). This does not mean, however, that a 1x DVD drive<br />
can read CDs at 9x rates: DVD drives actually spin at a rate that is just under three times faster than a<br />
CD-ROM drive of the same speed. So, a 1x DVD drive spins at about the same rotational speed as a<br />
Table <strong>13</strong>.20 DVD Speeds and Transfer Rates<br />
Column 1 Column 2 Column 3 Column 4 Column 5 Column 6 Column 7<br />
Time Time Transfer Actual Minimum<br />
Advertised to Read to Read Rate DVD Speed Transfer Average<br />
DVD-ROM Speed Single Layer Dual Layer (Bytes/sec) Minimum Rate if CAV DVD Speed<br />
(Max. if CAV) DVD if CLV DVD if CLV (Max. if CAV) if CAV (Bytes/sec) if CAV<br />
1x 56.5 51.4 1,384,615 0.4x 553,846 0.7x<br />
2x 28.3 25.7 2,769,231 0.8x 1,107,692 1.4x<br />
4x 14.1 12.8 5,538,462 1.7x 2,353,846 2.9x<br />
6x 9.4 8.6 8,307,692 2.5x 3,461,538 4.3x<br />
8x 7.1 6.4 11,076,923 3.3x 4,569,231 5.7x<br />
10x 5.7 5.1 <strong>13</strong>,846,154 4.1x 5,676,923 7.1x<br />
12x 4.7 4.3 16,615,385 5.0x 6,923,077 8.5x<br />
16x 3.5 3.2 22,153,846 6.6x 9,<strong>13</strong>8,462 11.3<br />
20x 2.8 2.6 27,692,308 8.3x 11,492,308 14.2<br />
24x 2.4 2.1 33,230,769 9.9x <strong>13</strong>,707,692 17.0<br />
32x 1.8 1.6 44,307,692 <strong>13</strong>.2x 18,276,923 22.6<br />
40x 1.4 1.3 55,384,615 16.6x 22,984,615 28.3<br />
48x 1.2 1.1 66,461,538 19.9x 27,553,846 34.0<br />
50x 1.1 1.0 69,230,769 20.7x 28,661,538 35.4
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