Hardware Reference
In-Depth Information
exist between codes. The 16-bit modulation codes are designed so that they will not viol-
ate the RLL 2,10 form without needing merge bits. Because the EFM used on CDs really
requires more than 17 bits for each byte (due to the added merge and sync bits), EFM+ is
slightly more efficient because only slightly more than 16 bits are generated for each byte
encoded.
Notethatalthoughnomorethanten0sareallowedinthemodulationgeneratedbyEFM+,
the sync bits added when physical sectors are written can have up to thirteen 0s, meaning
a time period of up to 14T between 1s written on the disc and pits or lands up to 14T in-
tervals or bit cells in length.
Recordable DVD Standards
ThehistoryofrecordableDVDdriveshasbeenatroubledone.ItdatesbacktoApril1997,
when the DVD Forum announced specifications for rewritable and recordable DVD:
DVD-RAM, and DVD-R. Later, it added DVD-RW to the mix. Dissatisfied with these
standards, the industry leaders in optical recording and drives formed their own group
calledtheDVD+RWAllianceandcreatedanotherstandard—DVD+RandDVD+RW.For
several years, drives based on one family of standards could not freely interchange media
with drives using the other family of standards.
Fortunately,allrecentdrivessupportbothDVD-R/RWandDVD+R/RWmedia,including
dual-layer (DL) DVD+R media, and most also support DVD-RAM. Thus, by using a
modern drive that supports all of these types of media, you can choose the right media for
a particular task. For example, use DVD-RAM for easy drag-and-drop file backups and
DVD-R for creating video DVDs compatible with older DVD set-top boxes.
Table 11.11
compares the competing recordable DVD standards, and
Table 11.12
breaks
down the compatibilities between the drives and media.
Table 11.11 Recordable DVD Standards
