5.1 At what speed are HD DVD discs written and read?
5.2 How much time does it take to write an HD DVD-R, HD DVD-RW, or HD DVD-RAM disc?
5.3 What rotational schemes fo HD DVD discs employ?
5.4 How might reading and writing speeds progress in the future?
At what speed are HD DVD discs written and read?
At single speed (1x) information is written to or read from an HD DVD disc at 4.36 MB (4,568,750 bytes or 36,550,000 bits) per second. Spinning the disc at higher velocities increases these rates, which are then expressed as multiples of these figures (e.g. 2x, 4x, 6x, etc.).
Putting HD DVD performance in perspective, 1x CD transfers 0.15 MB (153,000 bytes) per second while DVD transfers 1.32 MB (1,385,000 bytes) and Blu-ray Disc (BD) transfers 4.29 MB (4,495,625 bytes) per second. In HD DVD terms 1x is equivalent to roughly 29.9x CD, 3.3x DVD or 1x BD (see chart).
HD DVD Read and Write
Average Data Transfer Rates
(transfer rates indicated in binary notation)
| Read/Write Speed | Transfer Rate (bytes/sec) | Transfer Rate (MB/sec) | Equivalent DVD Speed | Equivalent CD Speed | Equivalent BD Speed |
| 1x | 4,568,750 | 4.36 | 3.3x | 29.9x | 1x |
| 2x | 9,137,500 | 8.71 | 6.6x | 59.7x | 2x |
How much time does it take to write an HD DVD-R, HD DVD-RW, or HD DVD-RAM disc?
HD DVD-R and HD DVD-RW specifications define 1x CLV writing and for HD DVD-RAM 1x ZCLV. Since 1x HD DVD writing transfers 4.36 MB (4,568,750 bytes) of data per second it takes, roughly, 55 minutes to write a full 15 GB (single-layer R/RW) disc or 74 minutes for a full 20 GB (single-layer RAM) disc.
In practice, recording time depends upon many factors including the writing speed supported by the recorder and disc, the amount of data to be written, if defect management or read-back verification is employed and the transfer rate of the data source.
What rotational schemes do HD DVD discs employ?
HD DVD-ROM/R/RW are currently read and written using Constant Linear Velocity (CLV) while HD DVD-RAM employs Zoned Constant Linear Velocity (ZCLV). As is the case for CD and DVD, Constant Linear Velocity (CLV) maintains an even data transfer rate as the optical head of the recorder, drive or player reads or writes from the inner (ID) to outer (OD) diameter of the disc. At 1x, the rotational speed of an HD DVD-ROM/R/RW disc decreases from roughly 2620 RPM to 1089 RPM (ID to OD) to maintain a constant linear velocity of 6.61 m/s. HD DVD-RAM employs a Zoned Constant Linear Velocity (ZCLV) scheme. The disc is divided into 19 zones with rotational speed kept constant within each but varied from zone to zone resulting in a relatively even data transfer rate and linear velocity of 5.64 to 6.03 m/s.
How might reading and writing speeds progress in the future?
HD DVD technology is in its infancy but if past optical storage industry experience is any indication, read and write speeds will increase rapidly. For example, manufacturers have already publicly discussed possible HD DVD-R/RW increases up to 4x.
At this early stage anticipating anything is merely speculation but it’s possible to make some informed predictions. From a practical perspective, spinning an optical disc at 10,000 RPM has long proven the realistic limit for half-height drives and 5,000 RPM for slim-types. Since a 12 cm HD DVD disc rotates between 2620 to 1089 RPM (ID to OD) at 1x speed, it is possible that 9x CAV (4x to 9x) will be the maximum potential ceiling for computer and 4.5x ZCLV or PCAV (2x to 4.5x) for portable HD DVD units. Generally speaking, rewritable and multi-layer discs are trickier so their maximum speeds will most likely be lower.