here - OSTA - Optical Storage Technology Association

6.10 Recommendations for CD Media
CD Media (CD-R and CD-RW) requires special consideration due to its nature. CD was
originally designed for read-only applications, which affects the way in which it is
written. The following guidelines are established to ensure interchange.
Each file and directory shall be described by a single direct ICB. The ICB should be
written after the file data to allow for data underruns during writing, which will cause
logical gaps in the file data. The ICB can be written afterward which will correctly
identify all extents of the file data. The ICB shall be written in the data track, the file
system track (if it exists), or both.
6.10.1 Use of UDF on CD-R media
ECMA 167 requires an Anchor Volume Descriptor Pointer (AVDP) at sector 256 and
either N or (N - 256), where N is the last recorded Physical Address on the media. UDF
requires that the AVDP be recorded at both sector 256 and sector (N - 256) when each
session is closed (2.2.3). The file system may be in an intermediate state before closing
and still be interchangeable, but not strictly in compliance with ECMA 167. In the
intermediate state, only one AVDP exists. It should exist at sector 256, but if this is not
possible due to a track reservation, it shall exist at sector 512.
Implementations should place file system control structures into virtual space and file
data into real space. Reader implementations may cache the entire VAT; the. The size of
the VAT should be considered by any UDF originating software. Computer based
implementations are expected to handle VAT sizes of at least 64K bytes; dedicated player
implementations may handle only smaller sizes.
The VAT may be located by using READ TRACK INFORMATION (for unfinished
media) or READ TOC or READ CD RECORDED CAPACITY for finished media. See
X3T10-1048D (SCSI-3 Multi Media Commands).
6.10.1.1 Requirements
• Writing shall use Mode 1 or Mode 2 Form 1 sectors. On one disc, either Mode 1 or
Mode 2 Form 1 shall be used; a mixture of Mode 1 and Mode 2 Form 1 sectors on
one disc is not allowed.
NOTE: According to the Multisession CD Specification, all data sessions on a disc
must be of the same type (Mode 1, or Mode 2 Form 1).
• If Mode 2 Form 1 is used, then the subheader bytes of all sectors used by the user data
files and by the UDF structures shall have the following value:
File number = 0
Channel number = 0
Submode = 08h
Coding information = 0
UDF 2.01
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