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DVD
Physical Specifications
Find out here how DVD discs differ from CDs and
how they contain much more data for a wide range of
applications. |
Please note that the descriptions below represent brief summaries of
the DVD specifications which can be obtained from the DVD
Forum.
The DVD technical specifications are contained in five books A to E published by the DVD
Forum.
| Book |
Name |
Part 1
Physical |
Part 2
File System |
Part 3
Appli- cation |
Ver |
A
|
DVD-ROM |
Read-only |
ISO 9660 + UDF |
undefined |
ver 1.01 |
B
|
DVD-Video |
Read-only |
UDF |
MPEG-2 video |
ver 1.1 |
C
|
DVD-Audio
|
Read-only |
UDF |
high quality audio |
ver 1.2 |
D
|
DVD-R
|
Write once |
UDF |
not defined |
ver 2.0 |
E
|
DVD-RAM
& DVD-RW
|
Rewritable |
UDF |
not defined |
ver 2.0 |
Physical
Parameters
The table below summarises the physical parameters of DVD and
compares them with those of CD and CD-ROM.
| Parameter |
CD |
DVD |
Comments |
| # layers |
1 |
single |
dual |
see Disc
Formats |
| Thickness (mm) |
1.2 |
0.6 |
2 x 0.6 mm |
| # sides |
1 |
2 |
DVD substrates bonded |
| Track pitch |
1.6 |
0.74 |
microns |
| Min pit length |
0.83 |
0.4 |
0.44 |
microns |
| Scan velocity |
1.3 |
3.49 |
3.84 |
m/sec |
| Wavelength (nm) |
780 |
635/650 |
red laser for DVD |
| Numerical aperture |
0.45 |
0.6 |
|
| Modulation |
EFM |
8 to 16 |
EFM is 8 to 17 |
| Error protection |
CIRC |
RSPC |
Block protection for DVD |
| 3rd layer ECC |
CD-ROM |
No |
Not needed for DVD |
| Subcode/Tracks |
Yes |
No |
Not needed for DVD |
DVD Sector Structure
The data on a DVD disc are organised as sectors of 2048 bytes plus
12 bytes of header data (see below). Blocks of 16 sectors are
error protected using RSPC RS PC (Reed Solomon Product Code), which
is block oriented and is more suitable for re-writable discs (with
packet writing) than CIRC which does not use a block format. The PI
and PO data are parity bytes calculated horizontally and vertically
over the data bytes.
In addition DVD uses an 8 to 16 modulation scheme giving pit lengths
of 3 to 14 (minimum to maximum length) compared with CD's 3 to 11 with
EFM modulation. This is only a small difference but does make the jitter
specification slightly tighter.
Burst Cutting Area
The Burst Cutting Area (BCA) is an annular area within the disc
hub where a bar code can be written for additional information such
as serial numbers. The BCA can be written during mastering and will
be common for all discs from that master or, more usually, will be
written using a YAG laser to 'cut' the barcode into the aluminium
reflective layer of the finished disc. The data stored in the BCA
can be from 12 bytes to 188 bytes in steps of 16 bytes. The
ill-fated Divx format used BCA to uniquely identify every disc. New
uses of this or similar technologies are being developed to use the
BCA as a unique, tamper-proof means of identifying individual discs.
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