+R disks according to this document in principle have to be recorded sequentially. To facilitate the recording of specific data at some pre-determined location on the disk at a later moment in time (such as for instance File System information), a Session can be divided into a number of Fragments. Inside such a Fragment the User Data shall be recorded sequentially from the inner side of the disk towards the outer side of the disk.
23.1 Opening a Session
New data can be added to the disk by appending to an Open Session. If there is no Open Session, a new Session has to be opened (see Table 13).
A new Session is opened by recording Buffer Zone A plus an SDCB (Session Disk Control Block: see 25.2) in the first ECC Block of the Inner Session Identification Zone (or by recording Reserved Zone 2 plus an SDCB in the first ECC Block of the Inner Disk Identification Zone in case of the first Session on a blank disk).
Table 13 — Details of opened Session n (example)
Session n-1
Data Data Zone User Data
Closure
Buffer Zone C 48 ECC Blocks with (00) Outer Session
Identification Zone 16 ECC Blocks with DCBs and/or (00)
Session n
Intro
Buffer Zone A 4 ECC Blocks with (00) Inner Session
Identification Zone 1 ECC Block with an SDCB blank Session
Control Data Zone blank
Buffer Zone B 4 ECC Blocks with (00)
Data Data Zone Reserved Fragment
(optional)
1 ECC Block for Run-in Incomplete Fragment with User Data blank
2 3 . 1 . 1 I n c o m p l e t e F r a g m e n t
When no Reserved Fragments (see 23.1.2) are created, all the remaining area of the Data Zone following Buffer Zone B is called the Incomplete Fragment. In the presence of Reserved Fragments, all the remaining area of the Data Zone following the last Reserved Fragment is called the Incomplete Fragment.
Until the Incomplete Fragment is closed (see 23.1.4), there shall be no Fragment item (see 25.2.1) for the Incomplete Fragment in any SDCB.
2 3 . 1 . 2 R e s e r ve d F r a g m e n t s
To allow for later on adding data, preceding already recorded User Data (such as for instance File System information), it is possible to create so-called Reserved Fragments. All Reserved Fragments in the Open Session shall be contiguous and non-overlapping, while the first Fragment shall start immediately after the end of Buffer Zone B.
Between any 2 Fragments there shall be 1 ECC Block for Run-in purposes. This ECC Block does not belong to any of the Fragments, and shall be recorded after the end of Reserved Fragment i at the same time the first ECC Block of Fragment (i+1) is recorded (see Figure 29).
2 3 . 1 . 2 . 1 A d d i n g a R e s e r ve d F r a g m e n t
If a new Reserved Fragment is defined, this Fragment shall start from the beginning of the Incomplete Fragment and at least include all data that have already been written to the Incomplete Fragment. The newly defined Reserved Fragment shall be Fragment n+1, where
n is the number of the previously last (Reserved) Fragment. A new SDCB shall be recorded
in the Identification Zone of the Session including a new Fragment item indicating the start and end addresses of the added Reserved Fragment (see 25.2.1).
Reserved Fragments can only be added as long as the number of free locations for SDCBs in the Inner Identification Zone of the current Session is larger than one. The last free location for an SDCB has to be preserved for closing the Session.
The area following the newly defined Reserved Fragment is designated to be the new Incomplete Fragment (n+2).
Fragm. -1n
Fragm. -1n
Fragm. -1n Fragm. n Fragm. +1n Fragm. +2n
Res.Fragm. n Res.Fragm. n Res.Fragm. +1n Closure Closure Closure Closure Intro Intro Intro Intro Inc.Fragm. ( +1)n Inc.Fragm. ( +2)n Session -1K Session -1K Session -1K Session K Session K Session K Session +1K Run-in Run-in Run-in Run-in Run-in
open session K with 1 Reserved Fragment
open session K with Reserved
added after writing in Incomplete
Fragment Fragment (n+1)
closing Session K
Figure 29 — Creating Reserved Fragments
2 3 . 1 . 3 R e c o r d i n g U s e r D a t a i n F r a g m e n t s
User Data added to the Data Zone shall be linked immediately to previously written User Data in the Incomplete Fragment or to previously written data in one of the Reserved Fragments.
2 3 . 1 . 4 C l o s i n g a F r a g m e n t
When a Reserved Fragment is closed, all blank areas in the Fragment shall be recorded with dummy data.
When the Incomplete Fragment is closed, a new SDCB shall be recorded in the Identification Zone of the Session including a new Fragment item indicating the start and end addresses of the (formerly) Incomplete Fragment (see 25.2). This formerly Incomplete Fragment shall not have unrecorded areas.
The area after the formerly Incomplete Fragment can be designated as the new Incomplete Fragment is case more User Data has to be added. For consistency reasons a Run-in Block shall be taken into account between the new Incomplete Fragment and the formerly Incomplete Fragment.
23.2 Closing a Session
To enable data retrieval from a Session by Read-Only devices, this Session and all preceding ones should be closed. A Session is closed by recording all blank areas in all Fragments with dummy data and recording all remaining parts in the Lead-in or Intro Zone and adding the Closure Zone.
When a Session is closed, the Incomplete Fragment is closed and shall be designated as Fragment m+1, where m is the number of the last (Reserved) Fragment preceding the Incomplete Fragment (see Figure 29).
The numbering of the Fragments shall be continuous over all Sessions (see Figure 29).
When the Session to be closed is the 191st Session, then the disk shall be finalized, instead of closing the Session (see 23.3).
Also when the remaining free space on the disk after closing the Session will become less than 128 ECC Blocks (2 048 Physical Sectors), the disk shall be finalized, instead of closing the Session (see 23.3.).
2 3 . 2 . 1 L e a d - i n / I n t r o Z o n e
The SDCB shall be updated, including the Incomplete Fragment as the last Fragment (n+2 in the example of Figure 29). In case multiple SDCBs have been recorded, the last written SDCB is the valid one.
In the Lead-in Zone the Control Data Zone shall be according to 18.8.
In each Intro the Session Control Data Zone shall be recorded with 40 ECC Blocks according to the format specified in 18.8 with the following settings:
Physical Format Information: